AN INTRODUCTION TO THE HUMAN BODY
Noninvasive Diagnostic Techniques
A noninvasive diagnostic technique is one that does not involve insertion of an instrument or device through the skin or a body opening.
In inspection, the examiner observes the body for any changes that deviate from normal. For example, a physician may examine the mouth cavity for evidence of disease. Following inspection, one or more additional techniques may be employed.
In palpation (pal-PA¯-shun; palp- gently touching) the examiner feels body surfaces with the hands. An example is palpating the abdomen to detect enlarged or tender internal organs or abnormal masses.
In auscultation (aws-kul-TA¯-shun; auscult- listening) the examiner listens to body sounds to evaluate the functioning of certain organs, often using a stethoscope to amplify the sounds. An example is auscultation of the lungs during breathing to check for crackling sounds associated with abnormal fluid accumulation.
In percussion (pur-KUSH-un; percus- beat through) the examiner taps on the body surface with the fingertips and listens to the resulting sound. Hollow cavities or spaces produce a different sound than solid organs. For example, percussion may reveal the abnormal presence of fluid in the lungs or air in the intestines. It may also provide information about the size, consistency, and position of an underlying structure.
An understanding of anatomy is important for the effective application of most of these diagnostic techniques.
An autopsy (AW-top-se¯ seeing with one’s own eyes) or necropsy is a postmortem (after death) examination of the body and dissection of its internal organs to confirm or determine the cause of death.
An autopsy can uncover the existence of diseases not detected during life, determine the extent of injuries, and explain how those injuries may have contributed to a person’s death. It also may provide more information about a disease, assist in the accumulation of statistical data, and educate health-care students. Moreover, an autopsy can reveal conditions that may affect offspring or siblings (such as congenital heart defects).
Sometimes an autopsy is legally required, such as during a criminal investigation. It may also be useful in resolving disputes between beneficiaries and insurance companies about the cause of death.
Diagnosis of Disease
Diagnosis (dıˉ-ag-NO¯ -sis; dia- through; -gnosis knowledge) is the science and skill of distinguishing one disorder or disease from another.
The patient’s symptoms and signs, his or her medical history, a physical exam, and laboratory tests provide the basis for making a diagnosis. Taking a medical history consists of collecting information about events that might be related to a patient’s illness. These include the chief complaint (primary reason for seeking medical attention), history of present illness, past medical problems, family medical problems, social history, and review of symptoms.
A physical examination is an orderly evaluation of the body and its functions. This process includes the noninvasive techniques of inspection, palpation, auscultation, and percussion, along with measurement of vital signs (temperature, pulse, respiratory rate, and blood pressure), and sometimes laboratory tests.
THE CHEMICAL LEVEL OF ORGANIZATION
Harmful and Beneficial Effects of Radiation
Radioactive isotopes may have either harmful or helpful effects. Their radiations can break apart molecules, posing a serious threat to the human body by producing tissue damage or causing various types of cancer.
Although the decay of naturally occurring radioactive isotopes typically releases just a small amount of radiation into the environment, localized accumulations can occur.
Radon-222, a colorless and odorless gas that is a naturally occurring radioactive breakdown product of uranium, may seep out of the soil and accumulate in buildings. It is not only associated with many cases of lung cancer in smokers but has also been implicated in many cases of lung cancer in nonsmokers.
Beneficial effects of certain radioisotopes include their use in medical imaging procedures to diagnose and treat certain disorders.
Some radioisotopes can be used as tracers to follow the movement of certain substances through the body.
- Thallium-201 is used to monitor blood flow through the heart during an exercise stress test.
- Iodine-131 is used to detect cancer of the thyroid gland and to assess its size and activity, and may also be used to destroy part of an overactive thyroid gland.
- Cesium-137 is used to treat advanced cervical cancer, and iridium-192 is used to treat prostate cancer.
Free Radicals and Antioxidants
There are several sources of free radicals, including exposure to ultraviolet radiation in sunlight, exposure to x-rays, and some reactions that occur during normal metabolic processes.
Certain harmful substances, such as carbon tetrachloride (a solvent used in dry cleaning), also give rise to free radicals when they participate in metabolic reactions in the body.
Among the many disorders, diseases, and conditions linked to oxygen-derived free radicals are cancer, atherosclerosis, Alzheimer’s disease, emphysema, diabetes mellitus, cataracts, macular degeneration, rheumatoid arthritis, and deterioration associated with aging.
Consuming more antioxidants—substances that inactivate oxygen-derived free radicals—is thought to slow the pace of damage caused by free radicals. Important dietary antioxidants include selenium, zinc, beta-carotene, and vitamins C and E. Red, blue, or purple fruits and vegetables contain high levels of antioxidants.
Fatty Acids in Health and Disease
As its name implies, a group of fatty acids called essential fatty acids (EFAs) is essential to human health. However, they cannot be made by the human body and must be obtained from foods or supplements. Among the more important EFAs are omega-3 fatty acids, omega-6 fatty acids, and cis-fatty acids.
An unsaturated fatty acid is not completely saturated with hydrogen atoms. The unsaturated fatty acid has a kink (bend) at the site of the double bond.
- If the fatty acid has just one double bond in the hydrocarbon chain, it is monounsaturated and it has just one kink.
- If a fatty acid has more than one double bond in the hydrocarbon chain, it is polyunsaturated and it contains more than one kink.
Omega-3 and omega-6 fatty acids are polyunsaturated fatty acids that are believed to work together to promote health. They may have a protective effect against heart disease and stroke by lowering total cholesterol, raising HDL (high-density lipoproteins or “good cholesterol”) and lowering LDL (low-density lipoproteins or “bad cholesterol”).
In addition, omega-3 and omega-6 fatty acids:
- decrease bone loss by increasing calcium utilization by the body;
- reduce symptoms of arthritis due to inflammation;
- promote wound healing;
- improve certain skin disorders (psoriasis, eczema, and acne);
- and improve mental functions.
Primary sources of omega-3 fatty acids include flax seed, fatty fish, oils that have large amounts of polyunsaturated fatty acids, fish oils, and walnuts.
Primary sources of omega-6 fatty acids include most processed foods (cereals, breads, white rice), eggs, baked goods, oils with large amounts of polyunsaturated fatty acids, and meats (especially organ meats, such as liver).
In oleic acid the hydrogen atoms on either side of the double bond are on the same side of the unsaturated fatty acid. Such cis-fatty acids are nutritionally beneficial unsaturated fatty acids that are used by the body to produce hormone like regulators and cell membranes.
However, when cis-fatty acids are heated, pressurized, and combined with a catalyst in a process called hydrogenation,
they are changed to unhealthy trans-fatty acids.
In trans fatty acids the hydrogen atoms are on opposite sides of the double bond of an unsaturated fatty acid. Hydrogenation is used by manufacturers to make vegetable oils solid at room temperature and less likely to turn rancid.
If oil used for frying is reused (like in fast food french fry machines), cis-fatty acids are converted to trans-fatty acids.
Among the adverse effects of trans-fatty acids are
- an increase in total cholesterol,
- a decrease in HDL & an increase in LDL,
- and an increase in triglycerides.
These effects, which can increase the risk of heart disease and other cardiovascular diseases, are similar to those caused by saturated fats.
THE CELLULAR LEVEL OF ORGANIZATION
Medical Uses of Isotonic,Hypertonic, and Hypotonic Solutions
A solution’s tonicity (toˉ-NIS-i-te¯; tonic tension) is a measure of the solution’s ability to change the volume of cells by altering their water content.
Any solution in which a cell—for example, a red blood cell (RBC)—maintains its normal shape and volume is an isotonic solution.
A different situation results if RBCs are placed in a hypotonic solution (hIˉ-poˉ-TON-ik; hypo- less than), a solution that has a lower concentration of solutes than the cytosol inside the RBCs. In this case, water molecules enter the cells faster than they leave, causing the RBCs to swell and eventually to burst(hemolysis).
A hypertonic solution (hIˉ-per-TON-ik; hyper- greater than) has a higher concentration of solutes than does the cytosol inside RBCs. One example of a hypertonic solution is a 2% NaCl solution. In such a solution, water molecules move out of the cells faster than they enter, causing the cells to shrink. Such shrinkage of cells is called crenation (kre-NAˉ -shun).
RBCs and other body cells may be damaged or destroyed if exposed to hypertonic or hypotonic solutions.
For this reason, most intravenous (IV) solutions, liquids infused into the blood of a vein, are isotonic. Examples are isotonic saline (0.9% NaCl) and D5W, which stands for dextrose 5% in water.
Sometimes infusion of a hypertonic solution such as mannitol (sugar alcohol) is useful to treat patients who have cerebral edema, excess interstitial fluid in the brain. Infusion of such a solution relieves fluid overload by causing osmosis of water from interstitial fluid into the blood. The kidneys then excrete the excess water from the blood into the urine.
Hypotonic solutions, given either orally or through an IV, can be used to treat people who are dehydrated. The water in the hypotonic solution moves from the blood into interstitial fluid and then into body cells to rehydrate them. Water and most sports drinks that you consume to “rehydrate” after a workout are hypotonic relative to your body cells.
Digitalis Increases Ca2 in Heart Muscle Cells
Digitalis often is given to patients with heart failure, a condition of weakened pumping action by the heart. Digitalis exerts its effect by slowing the action of the sodium–potassium pumps, which lets more Na accumulate inside heart muscle cells. The result is a decreased Na concentration gradient across the plasma membrane, which causes the Na–Ca2 anti porters to slow down.
As a result, more Ca2 remains inside heart muscle cells. The slight increase in the level of Ca2 in the cytosol of heart muscle cells increases the force of their contractions and thus strengthens the force of the heartbeat
Viruses and Receptor- Mediated Endocytosis
Although receptor-mediated endocytosis normally imports needed materials, some viruses are able to use this mechanism to enter and infect body cells.
For example, the human immunodeficiency virus (HIV), which causes acquired immunodeficiency syndrome (AIDS), can attach to a receptor called CD4. This receptor is present in the plasma membrane of white blood cells called helper T cells. After binding to CD4, HIV enters the helper T cell via receptor mediated endocytosis.
Phagocytosis and Microbes
Phagocytosis is a vital defense mechanism that helps protect the body from disease. Macrophages dispose of invading microbes and billions of aged, worn-out red blood cells every day; neutrophils also help rid the body of invading microbes. Pus is a mixture of dead neutrophils, macrophages, and tissue cells and fluid in an infected wound.
Cilia and Smoking
The movement of cilia is paralyzed by nicotine in cigarette smoke. For this reason, smokers cough often to remove foreign particles from their airways.
Cells that line the uterine (fallopian) tubes also have cilia that sweep oocytes (egg cells) toward the uterus, and females who smoke have an increased risk of ectopic (outside the uterus) pregnancy.
THE TISSUE LEVEL OF ORGANIZATION
A biopsy (BI¯-op-se¯; bio- life; -opsy to view) is the removal of a sample of living tissue for microscopic examination. This procedure is used to help diagnose many disorders, especially cancer, and to discover the cause of unexplained infections and inflammations.
Both normal and potentially diseased tissues are removed for purposes of comparison. Once the tissue samples are removed, either surgically or through a needle and syringe, they may be preserved, stained to highlight special properties, or cut into thin sections for microscopic observation.
Sometimes a biopsy is conducted while a patient is anesthetized during surgery to help a physician determine the most appropriate treatment. For example, if a biopsy of thyroid tissue reveals malignant cells, the surgeon can proceed immediately with the most appropriate procedure.
Basement Membranes and Disease
Under certain conditions, basement membranes become markedly thickened, due to increased production of collagen and laminin. In untreated cases of diabetes mellitus, the basement membrane of small blood vessels (capillaries) thickens, especially in the eyes and kidneys. Because of this the blood vessels cannot function properly and blindness and kidney failure may result.
A Papanicolaou test (pa-pa-NI-ko¯ -lo¯), also called a Pap test or Pap smear, involves collection and microscopic examination of epithelial cells that have been scraped off the apical layer of a tissue.
A very common type of Pap test involves examining the cells from the nonkeratinized stratified squamous epithelium of the vagina and cervix (inferior portion) of the uterus. This type of Pap test is performed mainly to detect early changes in the cells of the female reproductive system that may indicate a precancerous condition or cancer. In performing a Pap smear, the cells are scraped from the tissue and then smeared on a microscope slide. The slides are then sent to a laboratory for analysis.
Scar tissue can form adhesions (ad-HE¯-zhuns; adhaero to stick to), abnormal joining of tissues. Adhesions commonly form in the abdomen around a site of previous inflammation such as an inflamed appendix, and they can develop after surgery.
Although adhesions do not always cause problems, they can decrease tissue flexibility, cause obstruction (such as in the intestine), and make a subsequent operation, such as a cesarean section (C-section), more difficult. In rare cases adhesions can result in infertility. An adhesiotomy, the surgical release of adhesions, may be required.
THE INTEGUMENTARY SYSTEM
Skin Color as a Diagnostic Clue
The color of skin and mucous membranes can provide clues for diagnosing certain conditions.
When blood is not picking up an adequate amount of oxygen from the lungs, as in someone who has stopped breathing, the mucous membranes, nail beds, and skin appear bluish or cyanotic (sı¯-a-NOT-ik; cyan- blue).
Jaundice (JON-dis; jaund- yellow) is due to a buildup of the yellow pigment bilirubin in the skin. This condition gives a yellowish appearance to the skin and the whites of the eyes, and usually indicates liver disease.
Erythema (er-e-THE¯-ma; eryth- red), redness of the skin, is caused by engorgement of capillaries in the dermis with blood due to skin injury, exposure to heat, infection, inflammation, or allergic reactions.
Pallor (PAL-or), or paleness of the skin, may occur in conditions such as shock and anemia. All skin color changes are observed most readily in people with light-colored skin and may be more difficult to discern in people with darker skin. However, examination of the nail beds and gums can provide some information about circulation in individuals with darker skin.
Hair and Hormones
At puberty, when the testes begin secreting significant quantities of androgens (masculinizing sex hormones), males develop the typical male pattern of hair growth throughout the body, including a beard and a hairy chest. In females at puberty, the ovaries and the adrenal glands produce small quantities of androgens, which promote hair growth throughout the body including the axillae and pubic region.
Occasionally, a tumor of the adrenal glands, testes, or ovaries produces an excessive amount of androgens. The result in females or prepubertal males is hirsutism (HER-soo-tizm; hirsut- shaggy), excessive body hair or body hair in areas that usually are not hairy.
Surprisingly, androgens also must be present for occurrence of the most common form of baldness, male-pattern baldness. In genetically predisposed adults, androgens inhibit hair growth.
Chemotherapy and Hair Loss
Chemotherapy is the treatment of disease, usually cancer, by means of chemical substances or drugs.
Chemotherapeutic agents interrupt the life cycle of rapidly dividing cancer cells. Unfortunately, the drugs also affect other rapidly dividing cells in the body, such as the hair matrix cells of a hair. It is for this reason that individuals undergoing chemotherapy experience hair loss. Since about 15% of the hair matrix cells of scalp hairs are in the resting stage, these cells are not affected by chemotherapy. Once chemotherapy is stopped, the hair matrix cells replace lost hair follicles and hair growth resumes.
During childhood, sebaceous glands are relatively small and inactive. At puberty, androgens from the testes, ovaries, and adrenal glands stimulate sebaceous glands to grow in size and increase their production of sebum.
Acne is an inflammation of sebaceous glands that usually begins at puberty, when the sebaceous glands are stimulated by androgens.
Sun Damage, Sunscreens, and Sunblocks
Although basking in the warmth of the sun may feel good, it is not a healthy practice. There are two forms of ultraviolet
radiation that affect the health of the skin.
Longer wavelength ultraviolet A (UVA) rays make up nearly 95% of the ultraviolet radiation that reaches the earth. UVA rays are not absorbed by the ozone layer. They penetrate the furthest into the skin, where they are absorbed by melanocytes and thus are involved in sun tanning. UVA rays also depress the immune system.
Shorter wavelength ultraviolet B (UVB) rays are partially absorbed by the ozone layer and do not penetrate the skin as deeply as UVA rays. UVB rays cause sunburn and are responsible for most of the tissue damage (production of oxygen free radicals which disrupt collagen and elastic fibers) that results in wrinkling and aging of the skin and cataract formation.
Both UVA and UVB rays are thought to cause skin cancer. Long-term overexposure to sunlight results in dilated blood vessels, age spots, freckles, and changes in skin texture. Exposure to ultraviolet radiation (either natural sunlight or the artificial light of a tanning booth) may also produce photosensitivity, a heightened reaction of the skin after consumption of certain medications or contact with certain substances. Photosensitivity is characterized by redness, itching, blistering, peeling, hives, and even shock.
Sunscreens are topically applied preparations that contain various chemical agents (such as benzophenone or one of its derivatives) that absorb UVB rays but let most of the UVA rays pass through.
Sunblocks are topically applied preparations that contain substances such as zinc oxide that reflect and scatter both UVB and UVA rays.
THE SKELETAL SYSTEM: BONE TISSUE
Remodeling and Orthodontics
Orthodontics (or-tho¯ -DON-tiks) is the branch of dentistry concerned with the prevention and correction of poorly aligned teeth. The movement of teeth by braces places a stress on the bone that forms the sockets that anchor the teeth. In response to this artificial stress, osteoclasts and osteoblasts remodel the sockets so that the teeth align properly.
A delicate balance exists between the actions of osteoclasts and osteoblasts.
Should too much new tissue be formed, the bones become abnormally thick and heavy. If too much mineral material is deposited in the bone, the surplus may form thick bumps, called spurs, on the bone that interfere with movement at joints.
Excessive loss of calcium or tissue weakens the bones, and they may break, as occurs in osteoporosis, or they may become too flexible, as in rickets and osteomalacia. Osteomalacia is a weakening of the bones, problems with bone formation or with the bone building process cause osteomalacia. Osteomalacia isn’t the same as osteoporosis. Osteoporosis is a weakening of living bone that has already been formed and is being remodeled.
In Paget’s disease, there is an excessive proliferation of osteoclasts so that bone resorption occurs faster than bone deposition. In response, osteoblasts attempt to compensate, but the new bone is weaker because it has a higher proportion of spongy to compact bone, mineralization is decreased, and the newly synthesized extracellular matrix contains abnormal proteins.
The newly formed bone, especially that of the pelvis, limbs, lower vertebrae, and skull, becomes enlarged, hard, and brittle and fractures easily.
Hormonal Abnormalities That Affect Height
Excessive or deficient secretion of hormones that normally control bone growth can cause a person to be abnormally tall or short.
- Oversecretion of hGH during childhood produces giantism, in which a person becomes much taller and heavier than normal.
- Undersecretion of hGH produces pituitary dwarfism, in which a person has short stature. (The usual adult height of a dwarf is under 4 feet 10 inches.) Although the head, trunk, and limbs of a pituitary dwarf are smaller than normal, they are proportionate. The condition can be treated medically with hGH until epiphyseal plate closure.
Oversecretion of hGH during adulthood is called acromegaly.
Although hGH cannot produce further lengthening of the long bones because the epiphyseal (growth) plates are already closed, the bones of the hands, feet, and jaws thicken and other tissues enlarge. In addition, the eyelids, lips, tongue, and nose enlarge, and the skin thickens and develops furrows, especially on the forehead and soles.
Achondroplasia (a¯ -kon-dro-PLA¯-ze¯-a; a- without; -chondro- cartilage; -plasia to mold) is an inherited condition in which the conversion of cartilage to bone is abnormal. It results in the most common type of dwarfism, called achondroplastic dwarfism. These individuals are typically about 4 feet tall as adults. They have an average-size trunk, short limbs, and a slightly enlarged head with a prominent forehead and flattened nose at the bridge. The condition is essentially untreatable, although some individuals opt for limb-lengthening surgery.
Treatments for Fractures
Treatments for fractures vary according to age, type of fracture, and the bone involved.
The ultimate goals of fracture treatment are:
- Realignment of the bone fragments,
- Immobilization to maintain realignment, and
- Restoration of function.
For bones to unite properly, the fractured ends must be brought into alignment. This process, called reduction, is commonly referred to as setting a fracture.
- In closed reduction, the fractured ends of a bone are brought into alignment by manual manipulation, and the skin remains intact.
- In open reduction, the fractured ends of a bone are brought into alignment by a surgical procedure using internal fixation devices such as screws, plates, pins, rods, and wires.
Following reduction, a fractured bone may be kept immobilized by a cast, sling, splint, elastic bandage, external fixation device, or a combination of these devices.
THE SKELETAL SYSTEM: THE AXIAL SKELETON
A black eye is a bruising around the eye, commonly due to an injury to the face, rather than an eye injury. In response to trauma, blood and other fluids accumulate in the space around the eye, causing the swelling and dark discoloration.
One cause might be a blow to the sharp ridge just superior to the supraorbital margin that fractures the frontal bone, resulting in bleeding. Another is a blow to the nose. Certain surgical procedures (face lift, eyelid surgery, jaw surgery, or nasal surgery) can also result in black eyes.
Cleft Palate and Cleft Lip
- Usually the palatine processes of the maxillary bones unite during weeks 10 to 12 of embryonic development. Failure to do so can result in one type of cleft palate.
- The condition may also involve incomplete fusion of the horizontal plates of the palatine bones.
- Another form of this condition, called cleft lip, involves a split in the upper lip.
Cleft lip and cleft palate often occur together. Depending on the extent and position of the cleft, speech and swallowing may be affected. In addition, children with cleft palate tend to have many ear infections, which can lead to hearing loss. Facial and oral surgeons recommend closure of cleft lip during the first few weeks following birth, and surgical results are excellent.
Repair of cleft palate typically is completed between 12 and 18 months of age, ideally before the child begins to talk. Because the palate is important for pronouncing consonants, speech therapy may be required, and orthodontic therapy may be needed to align the teeth. Recent research strongly suggests that supplementation with folic acid (one of the B vitamins) during early pregnancy decreases the incidence of cleft palate and cleft lip. The mechanism behind this is not yet understood.
Temporomandibular Joint Syndrome
One problem associated with the temporomandibular joint is temporomandibular joint (TMJ) syndrome. It is characterized by
- dull pain around the ear,
- tenderness of the jaw muscles,
- a clicking or popping noise when opening or closing the mouth,
- limited or abnormal opening of the mouth,
- tooth sensitivity,
- and abnormal wearing of the teeth.
TMJ syndrome can be caused by improperly aligned teeth, grinding or clenching the teeth, trauma to the head and neck, or arthritis.
Treatments include application of moist heat or ice, limiting the diet to soft foods, administration of pain relievers such as aspirin, muscle retraining, use of a splint or bite plate to reduce clenching and teeth grinding (especially when worn at night), adjustment or reshaping of the teeth (orthodontic treatment), and surgery.
Deviated Nasal Septum
A deviated nasal septum is one that does not run along the midline of the nasal cavity. It deviates (bends) to one side.
A blow to the nose can easily damage, or break, this delicate septum of bone and displace and damage the cartilage. Often, when a broken nasal septum heals, the bones and cartilage deviate to one side or the other.
This deviated septum can block airflow into the constricted side of the nose, making it difficult to breathe through that half of the nasal cavity. The deviation usually occurs at the junction of the vomer bone with the septal cartilage. Septal deviations may also occur due to developmental abnormality.
If the deviation is severe, it may block the nasal passageway entirely. Even a partial blockage may lead to infection. If inflammation occurs, it may cause nasal congestion, blockage of the paranasal sinus openings, chronic sinusitis, headache, and nosebleeds. The condition usually can be corrected or improved surgically.
Sinusitis (sı¯n-u¯-SIˉ -tis) is an inflammation of the mucous membrane of one or more paranasal sinuses. It may be
- a microbial infection (virus, bacterium, or fungus),
- allergic reactions,
- nasal polyps,
- or a severely deviated nasal septum.
If the inflammation or an obstruction blocks the drainage of mucus into the nasal cavity, fluid pressure builds up in the paranasal sinuses, and a sinus headache may develop. Other symptoms may include nasal congestion, inability to smell, fever, and cough.
Treatment options include decongestant sprays or drops, oral decongestants, nasal corticosteroids, antibiotics, analgesics to relieve pain, warm compresses, and surgery.
Rib Fractures, Dislocations, and Separations
Rib fractures are the most common chest injuries.
They usually result from direct blows, most often from impact with a steering wheel, falls, or crushing injuries to the chest.
Ribs tend to break at the point where the greatest force is applied, but they may also break at their weakest point—the site of greatest curvature, just anterior to the costal angle. The middle ribs are the most commonly fractured.
In some cases, fractured ribs may puncture the heart, great vessels of the heart, lungs, trachea, bronchi, esophagus, spleen, liver, and kidneys. Rib fractures are usually quite painful. Rib fractures are no longer bound with bandages because of the pneumonia that would result from lack of proper lung ventilation.
Dislocated ribs, which are common in body contact sports, involve displacement of a costal cartilage from the sternum, with resulting pain, especially during deep inhalations.
Separated ribs involve displacement of a rib and its costal cartilage; as a result, a rib may move superiorly, overriding the rib above and causing severe pain.
THE SKELETAL SYSTEM: THE APPENDICULAR SKELETON
The clavicle transmits mechanical force from the upper limb to the trunk. If the force transmitted to the clavicle is excessive, as when you fall on your outstretched arm, a fractured clavicle may result. A fractured clavicle may also result from a blow to the superior part of the anterior thorax, for example, as a result of an impact following an automobile accident.
The clavicle is one of the most frequently broken bones in the body. Because the junction of the two curves of the clavicle is its weakest point, the clavicular midregion is the most frequent fracture site.
Even in the absence of fracture, compression of the clavicle as a result of automobile accidents involving the use of shoulder harness seatbelts often causes damage to the brachial plexus (the network of nerves that enter the upper limb), which lies between the clavicle and the second rib.
A fractured clavicle is usually treated with a figure-of-8 sling to keep the arm from moving outward.
A boxer’s fracture is a fracture of the fifth metacarpal, usually near the head of the bone. It frequently occurs after a person punches another person or an object, such as a wall. It is characterized by pain, swelling, and tenderness. There may also be a bump on the side of the hand. Treatment is either by casting or surgery, and the fracture usually heals in about 6 weeks.
Pelvimetry is the measurement of the size of the inlet and outlet of the birth canal, which may be done by ultrasonography or physical examination. Measurement of the pelvic cavity in pregnant females is important because the fetus must pass through the narrower opening of the pelvis at birth. A cesarean section is usually planned if it is determined that the pelvic cavity is too small to permit passage of the baby.
Patellofemoral Stress Syndrome
Patellofemoral stress syndrome (runner’s knee) is one of the most common problems runners experience.
During normal flexion and extension of the knee, the patella tracks (glides) superiorly and inferiorly in the groove between the femoral condyles. In patellofemoral stress syndrome, normal tracking does not occur; instead, the patella tracks laterally as well as superiorly and inferiorly, and the increased pressure on the joint causes aching or tenderness around or under the patella.
The pain typically occurs after a person has been sitting for a while, especially after exercise. It is worsened by squatting or walking down stairs. One cause of runner’s knee is constantly walking, running, or jogging on the same side of the road. Other predisposing factors include running on hills, running long distances, and an anatomical deformity called genu valgum.
Bone grafting generally consists of taking a piece of bone, along with its periosteum and nutrient artery, from one part of the body to replace missing bone in another part of the body.
The transplanted bone restores the blood supply to the transplanted site, and healing occurs as in a fracture. The fibula is a common source of bone for grafting because even after a piece of the fibula has been removed, walking, running, and jumping can be normal. Recall that the tibia is the weight-bearing bone of the leg.
Fractures of the Metatarsals
Fractures of the metatarsals occur when a heavy object falls on the foot or when a heavy object rolls over the foot.
Such fractures are also common among dancers, especially ballet dancers. If a ballet dancer is on the tip of her toes and loses her balance, the full body weight is placed on the metatarsals, causing one or more of them to fracture.
Flatfoot and Clawfoot
The bones composing the arches of the foot are held in position by ligaments and tendons. If these ligaments and tendons are weakened, the height of the medial longitudinal arch may decrease or “fall.”
The result is flatfoot, the causes of which include excessive weight, postural abnormalities, weakened supporting tissues, and genetic predisposition. Fallen arches may lead to
- inflammation of the fascia of the sole (plantar fasciitis),
- Achilles tendinitis,
- shin splints,
- stress fractures,
- and calluses.
A custom- designed arch support often is prescribed to treat flatfoot.
Clawfoot is a condition in which the medial longitudinal arch is abnormally elevated. It is often caused by muscle deformities, such as may occur in diabetics whose neurological lesions lead to atrophy of muscles of the foot.
Autologous Chondrocyte Implantation
When there is damage to articular cartilage in the knee joint, especially involving the femur, there is an alternative to partial or total knee replacement called autologous chondrocyte implantation (ACI) (aw-TOL-o-gus).
Candidates for ACI have cartilage damage due to acute or repetitive trauma, not arthritis. In the procedure, healthy chondrocytes (cartilage cells) are taken from an area of the femoral condyle that is not weight-bearing and sent to a laboratory, where they are cultured for 4 to 5 weeks to generate between 5 million and 10 million cells. When the cultured cells are available, the implantation takes place.
The damaged area is prepared by removing dead cartilage from the defect, which is covered by a piece of periosteum, usually taken from the tibia. Then the cultured chondrocytes are injected under the periosteum, where they will grow and mature over time. The patient can put the full weight of the body on the knee in about 10 to 12 weeks.
Torn Cartilage and Arthroscopy
The tearing of menisci in the knee, commonly called torn cartilage, occurs often among athletes. Such damaged cartilage will begin to wear and may cause arthritis to develop unless the damaged cartilage is treated surgically.
Years ago, if a patient had torn cartilage, the entire meniscus was removed by a procedure called a meniscectomy (men-i-SEK-toˉ-meˉ). The problem was that over time the articular cartilage was worn away more quickly. Currently, surgeons perform a partial meniscectomy, in which only the torn segment of the meniscus is removed. Surgical repair of the torn cartilage may be assisted by arthroscopy (ar-THROS-koˉ -peˉ; -scopy observation).
This minimally invasive procedure involves examination of the interior of a joint, usually the knee, with an arthroscope, a lighted, pencil-thin fiber optic camera used for visualizing the nature and extent of damage. Arthroscopy is also used to monitor the progression of disease and the effects of therapy.
The insertion of surgical instruments through other incisions also enables a physician to remove torn cartilage and repair damaged cruciate ligaments in the knee; obtain tissue samples for analysis; and perform surgery on other joints, such as the shoulder, elbow, ankle, and wrist.
An acute or chronic inflammation of a bursa, called bursitis (bur-SIˉ -tis), is usually caused by irritation from repeated, excessive exertion of a joint. The condition may also be caused by trauma, by an acute or chronic infection (including syphilis and tuberculosis), or by rheumatoid arthritis.
Symptoms include pain, swelling, tenderness, and limited movement. Treatment may include oral anti-inflammatory agents and injections of cortisollike steroids.
Rotator Cuff Injury, Dislocated and Separated Shoulder, and Torn Glenoid Labrum
Rotator cuff injury is a strain or tear in the rotator cuff muscles and is a common injury among baseball pitchers, volleyball players, racket sports players, swimmers, and violinists, due to shoulder movements that involve vigorous circumduction. It also occurs as a result of wear and tear, aging, trauma, poor posture, improper lifting, and repetitive motions in certain jobs, such as placing items on a shelf above your head.
Most often, there is tearing of the supraspinatus muscle tendon of the rotator cuff. This tendon is especially predisposed to wear and tear because of its location between the head of the humerus and acromion of the scapula, which compresses the tendon during shoulder movements. Poor posture and poor body mechanics also increase compression of the supraspinatus muscle tendon.
The joint most commonly dislocated in adults is the shoulder joint because its socket is quite shallow and the bones are held together by supporting muscles. Usually in a dislocated shoulder, the head of the humerus becomes displaced inferiorly, where the articular capsule is least protected.
Dislocations of the mandible, elbow, fingers, knee, or hip are less common.
Dislocations are treated with rest, ice, pain relievers, manual manipulation, or surgery followed by use of a sling and physical therapy.
A separated shoulder actually refers to an injury not to the shoulder joint but to the acromioclavicular joint, a joint formed by the acromion of the scapula and the acromial end of the clavicle. This condition is usually the result of forceful trauma to the joint, as when the shoulder strikes the ground in a fall.
Treatment options are similar to those for treating a dislocated shoulder, although surgery is rarely needed.
In a torn glenoid labrum, the fibrocartilaginous labrum may tear away from the glenoid cavity. This causes the joint to catch or feel like it’s slipping out of place. The shoulder may indeed become dislocated as a result. A torn labrum is reattached to the glenoid surgically with anchors and sutures. The repaired joint is more stable.
Tennis Elbow, Little-league elbow, and Dislocation of the Radial Head
Tennis elbow most commonly refers to pain at or near the lateral epicondyle of the humerus, usually caused by an improperly executed backhand. The extensor muscles strain or sprain, resulting in pain.
Little-league elbow, inflammation of the medial epicondyle, typically develops as a result of a heavy pitching schedule and/or a schedule that involves throwing curve balls, especially among youngsters.
In this disorder, the elbow joint may enlarge, fragment, or separate.
A dislocation of the radial head is the most common upper limb dislocation in children. In this injury, the head of the radius slides past or ruptures the radial anular ligament, a ligament that forms a collar around the head of the radius at the proximal radioulnar joint.
Dislocation is most apt to occur when a strong pull is applied to the forearm while it is extended and supinated, for instance, while swinging a child around with outstretched arms.
The knee joint is the joint most vulnerable to damage because it is a mobile, weight-bearing joint and its stability depends almost entirely on its associated ligaments and muscles. Further, there is no complementary fit between the surfaces of the articulating bones.
Following are several kinds of knee injuries.
A swollen knee may occur immediately or hours after an injury. The initial swelling is due to escape of blood from damaged blood vessels adjacent to areas of injury, including:
- rupture of the anterior cruciate ligament,
- damage to synovial membranes,
- torn menisci, fractures,
- or collateral ligament sprains.
Delayed swelling is due to excessive production of synovial fluid, a condition commonly referred to as “water on the knee.”
The firm attachment of the tibial collateral ligament to the medial meniscus is clinically significant because tearing of the ligament typically also results in tearing of the meniscus. Such an injury may occur in sports such as football and rugby when the knee receives a blow from the lateral side while the foot is fixed on the ground. The force of the blow may also tear the anterior cruciate ligament, which is also connected to the medial meniscus.
The term “unhappy triad” is applied to a knee injury that involves damage to the three components of the knee at the same time:
- the tibial collateral ligament,
- medial meniscus,
- and anterior cruciate ligament.
A dislocated knee refers to the displacement of the tibia relative to the femur. The most common type is dislocation anteriorly, resulting from hyperextension of the knee. A frequent consequence of a dislocated knee is damage to the popliteal artery.
If no surgery is required, treatment of knee injuries involves PRICE (protection, rest, ice, compression, and elevation) with some strengthening exercises and perhaps physical therapy.
Fibromyalgia (fı¯-bro¯-mı¯-AL-je¯-a; -algia painful condition) is a chronic, painful, nonarticular rheumatic disorder that affects the fibrous connective tissue components of muscles, tendons, and ligaments.
A striking sign is pain that results from gentle pressure at specific “tender points.” Even without pressure, there is pain, tenderness, and stiffness of muscles, tendons, and surrounding soft tissues. Besides muscle pain, those with fibromyalgia report severe fatigue, poor sleep, headaches, depression, irritable bowel syndrome, and inability to carry out their daily activities.
There is no specific identifiable cause. Treatment consists of stress reduction, regular exercise, application of heat, gentle massage, physical therapy, medication for pain, and a low-dose antidepressant to help improve sleep.
Muscular Hypertrophy, Fibrosis, and Atrophy
The muscle growth that occurs after birth occurs by enlargement of existing muscle fibers, called muscular hypertrophy
(hı¯-PER-tro¯ -fe¯; hyper- above or excessive; -trophy nourishment).
Muscular hypertrophy is due to increased production of myofibrils, mitochondria, sarcoplasmic reticulum, and other organelles. It results from very forceful, repetitive muscular activity, such as strength training. Because hypertrophied muscles contain more myofibrils, they are capable of more forceful contractions.
During childhood, human growth hormone and other hormones stimulate an increase in the size of skeletal muscle fibers. The hormone testosterone promotes further enlargement of muscle fibers.
A few myoblasts do persist in mature skeletal muscle as satellite cells. Satellite cells retain the capacity to fuse with one another or with damaged muscle fibers to regenerate functional muscle fibers. However, when the number of new skeletal muscle fibers that can be formed by satellite cells is not enough to compensate for significant skeletal muscle damage or degeneration, the muscular tissue undergoes fibrosis, the replacement of muscle fibers by fibrous scar tissue.
Muscular atrophy (AT-ro¯ -fe¯; a- without, -trophy nourishment) is a decrease in size of individual muscle fibers as a result of progressive loss of myofibrils. Atrophy that occurs because muscles are not used is termed disuse atrophy. Bedridden individuals and people with casts experience disuse atrophy because the flow of nerve impulses to inactive skeletal muscle is greatly reduced, but the condition is reversible.
If instead its nerve supply is disrupted or cut, the muscle undergoes denervation atrophy. Over a period of 6 months to 2 years, the muscle shrinks to about one-fourth its original size, and its fibers are irreversibly replaced by fibrous connective tissue.
After death, cellular membranes become leaky. Calcium ions leak out of the sarcoplasmic reticulum into the sarcoplasm and allow myosin heads to bind to actin. ATP synthesis ceases shortly after breathing stops, however, so the cross-bridges cannot detach from actin.
The resulting condition, in which muscles are in a state of rigidity (cannot contract or stretch), is called rigor mortis (rigidity of death). Rigor mortis begins 3–4 hours after death and lasts about 24 hours; then it disappears as proteolytic enzymes from lysosomes digest the cross-bridges.
Electromyography (EMG) (e-lek-tro¯-mı¯-OG-ra-fe¯; electro- electricity; -myo- muscle; -graph to write) is a test that measures the electrical activity (muscle action potentials) in resting and contracting muscles.
Normally, resting muscle produces no electrical activity; a slight contraction produces some electrical activity; and a more forceful contraction produces increased electrical activity.
In the procedure, a ground electrode is placed over the muscle to be tested to eliminate background electrical activity. Then, a fine needle attached by wires to a recording instrument is inserted into the muscle. The electrical activity of the muscle is displayed as waves on an oscilloscope and heard through a loudspeaker.
EMG helps to determine if muscle weakness or paralysis is due to a malfunction of the muscle itself or the nerves supplying the muscle. EMG is also used to diagnose certain muscle disorders, such as muscular dystrophy, and to understand which muscles function during complex movements.
Creatine is both synthesized in the body and derived from foods such as milk, red meat, and some fish. Adults need to synthesize and ingest a total of about 2 grams of creatine daily to make up for the urinary loss of creatinine, the breakdown product of creatine.
Some studies have demonstrated improved performance from creatine supplementation during explosive movements, such as sprinting. Other studies, however, have failed to find a performance-enhancing effect of creatine supplementation. Moreover, ingesting extra creatine decreases the body’s own synthesis of creatine, and it is not known whether natural synthesis recovers after long-term creatine supplementation. In addition, creatine supplementation can cause dehydration and may cause kidney dysfunction.
Further research is needed to determine both the long-term safety and the value of creatine supplementation.
Anaerobic Training versus Aerobic Training
Regular, repeated activities such as jogging or aerobic dancing increase the supply of oxygen–rich blood available to skeletal muscles for aerobic respiration.
By contrast, activities such as weight lifting rely more on anaerobic production of ATP through glycolysis. Such anaerobic training activities stimulate synthesis of muscle proteins and result, over time, in increased muscle size (muscle hypertrophy). Athletes who engage in anaerobic training should have a diet that includes an adequate amount of proteins. This protein intake will allow the body to synthesize muscle proteins and to increase muscle mass.
As a result, aerobic training builds endurance for prolonged activities; in contrast, anaerobic training builds muscle strength for short-term feats. Interval training is a workout regimen that incorporates both types of training—for example, alternating sprints with jogging.
Hypotonia and Hypertonia
Hypotonia (hı¯-po¯ -TO¯ -ne¯-a; hypo- below) refers to decreased or lost muscle tone. Such muscles are said to be flaccid. Flaccid muscles are loose and appear flattened rather than rounded. Certain disorders of the nervous system and disruptions in the balance of electrolytes (especially sodium, calcium, and, to a lesser extent, magnesium) may result in flaccid paralysis (pa-RAL-i-sis), which is characterized by loss of muscle tone, loss or reduction of tendon reflexes, and atrophy (wasting away) and degeneration of muscles.
Hypertonia (hı¯-per-TO¯ -ne¯-a; hyper- above) refers to increased muscle tone and is expressed in two ways:
- or rigidity.
Spasticity (spas-TIS-i-te¯) is characterized by increased muscle tone (stiffness) associated with an increase in tendon reflexes and pathological reflexes (such as the Babinski sign, in which the great toe extends with or without fanning of the other toes in response to stroking the outer margin of the sole). Certain disorders of the nervous system and electrolyte disturbances such as those previously noted may result in spastic paralysis, partial paralysis in which the muscles exhibit spasticity.
Rigidity refers to increased muscle tone in which reflexes are not affected, as occurs in tetanus. Tetanus is a disease caused by a bacterium, Clostridium tetani, that enters the body through exposed wounds. It leads to muscle stiffness and spasms that can make breathing difficult and can become life-threatening as a result.
The bacteria produce a toxin that interferes with the nerves controlling the muscles. The first signs are typically spasms and stiffness in the muscles of the face and jaws.
The use of anabolic steroids (an-a-BOL-ik to build up proteins), or “roids,” by athletes has received widespread attention.
These steroid hormones, similar to testosterone, are taken to increase muscle size by increasing the synthesis of proteins in muscle and thus increasing strength during athletic contests.
However, the large doses needed to produce an effect have damaging, sometimes even devastating side effects, including
- liver cancer,
- kidney damage,
- increased risk of heart disease,
- stunted growth,
- wide mood swings,
- increased acne,
- and increased irritability and aggression.
Additionally, females who take anabolic steroids may experience
- atrophy of the breasts and uterus,
- menstrual irregularities,
- facial hair growth,
- and deepening of the voice.
Males may experience
- diminished testosterone secretion,
- atrophy of the testes,
- and baldness.
An intramuscular (IM) injection penetrates the skin and subcutaneous layer to enter the muscle itself. Intramuscular injections are preferred when prompt absorption is desired, when larger doses than can be given subcutaneously are indicated, or when the drug is too irritating to give subcutaneously.
The common sites for intramuscular injections include the
- gluteus medius muscle of the buttock,
- lateral side of the thigh in the midportion of the vastus lateralis muscle,
- and the deltoid muscle of the shoulder.
Muscles in these areas, especially the gluteal muscles in the buttock, are fairly thick, and absorption is promoted by their extensive blood supply.
To avoid injury, intramuscular injections are given deep within the muscle, away from major nerves and blood vessels. Intramuscular injections have a faster speed of delivery than oral medications but are slower than intravenous infusions.
Benefits of Stretching
The overall goal of stretching is to achieve normal range of motion of joints and mobility of soft tissues surrounding the joints. For most individuals, the best stretching routine involves static stretching, that is, slow sustained stretching that holds a muscle in a lengthened position.
The muscles should be stretched to the point of slight discomfort (not pain) and held for about 30 seconds.
Stretching should be done after warming up to increase the range of motion most effectively.
- 1. Improved physical performance. A flexible joint has the ability to move through a greater range of motion, which improves performance.
- 2. Decreased risk of injury. Stretching decreases resistance in various soft tissues so there is less likelihood of exceeding maximum tissue extensibility during an activity (i.e., injuring the soft tissues).
- 3. Reduced muscle soreness. Stretching can reduce some of the muscle soreness that results after exercise.
- 4. Improved posture. Poor posture results from improper position of various parts of the body and the effects of gravity over a number of years. Stretching can help realign soft tissues to improve and maintain good posture.
Bell’s palsy, also known as facial paralysis, is a unilateral paralysis of the muscles of facial expression. It is due to damage or disease of the facial (VII) nerve. Possible causes include inflammation of the facial nerve due to an ear infection, ear surgery that damages the facial nerve, or infection by the herpes simplex virus.
The paralysis causes the entire side of the face to droop in severe cases. The person cannot wrinkle the forehead, close the eye, or pucker the lips on the affected side. Drooling and difficulty in swallowing also occur.
Eighty percent of patients recover completely within a few weeks to a few months. For others, paralysis is permanent.
The symptoms of Bell’s palsy mimic those of a stroke.
Strabismus (stra-BIZ-mus; strabismos squinting) is a condition in which the two eyeballs are not properly aligned. This can be hereditary or it can be due to birth injuries, poor attachments of the muscles, problems with the brain’s control center, or localized disease. Strabismus can be constant or intermittent.
In strabismus,each eye sends an image to a different area of the brain and because the brain usually ignores the messages sent by one of the eyes, the ignored eye becomes weaker; hence “lazy eye,” or amblyopia, develops.
External strabismus results when a lesion in the oculomotor (III) nerve causes the eyeball to move laterally when at rest, and results in an inability to move the eyeball medially and inferiorly. A lesion in the abducens (VI) nerve results in internal strabismus, a condition in which the eyeball moves medially when at rest and cannot move laterally.
Treatment options for strabismus depend on the specific type of problem and include surgery, visual therapy (retraining the brain’s control center), and orthoptics (eye muscle training to straighten the eyes).
Gravity and the Mandible
Three of the four muscles of mastication close the mandible and only the lateral pterygoid opens the mouth. The force of gravity on the mandible offsets this imbalance. When the masseter, temporalis, and medial pterygoid muscles relax, the mandible drops.
Now you know why the mouth of many persons, particularly the elderly, is open while the person is asleep in a chair. In contrast, astronauts in zero gravity must work hard to open their mouths.
Intubation during Anesthesia
When general anesthesia is administered during surgery, a total relaxation of the muscles results. Once the various types of drugs for anesthesia have been given (especially the paralytic agents), the patient’s airway must be protected and the lungs ventilated because the muscles involved with respiration are among those paralyzed. Paralysis of the genioglossus muscle causes the tongue to fall posteriorly, which may obstruct the airway to the lungs.
To avoid this, the mandible is either manually thrust forward and held in place (known as the “sniffing position”), or a tube is inserted from the lips through the laryngopharynx (inferior portion of the throat) into the trachea (endotracheal intubation). People can also be intubated nasally (through the nose).
Dysphagia (dis-FA¯ -je¯ -a; dys- abnormal; -phagia to eat) is a clinical term for difficulty in swallowing.
Some individuals are unable to swallow while others have difficulty swallowing liquids, foods, or saliva.
Causes include nervous system disorders that weaken or damage muscles of deglutition (stroke, Parkinson’s disease,
cerebral palsy); infections; cancer of the head, neck, or esophagus; and injuries to the head, neck, or chest.
A hernia (HER-ne¯-a) is a protrusion of an organ through a structure that normally contains it, which creates a lump that can be seen or felt through the skin’s surface. The inguinal region is a weak area in the abdominal wall. It is often the site of an inguinal hernia, a rupture or separation of a portion of the inguinal area of the abdominal wall resulting in the protrusion of a part of the small intestine.
A hernia is much more common in males than in females because the inguinal canals in males are larger to accommodate the spermatic cord and ilioinguinal nerve.
Treatment of hernias most often involves surgery. The organ that protrudes is “tucked” back into the abdominal cavity and the defect in the abdominal muscles is repaired. In addition, a mesh is often applied to reinforce the area of weakness.
Injury of Levator Ani and Urinary Stress Incontinence
During childbirth, the levator ani muscle supports the head of the fetus, and the muscle may be injured during a difficult childbirth or traumatized during an episiotomy (a cut made with surgical scissors to prevent or direct tearing of the perineum during the birth of a baby). The consequence of such injuries may be urinary stress incontinence, that is, the leakage of urine whenever intra-abdominal pressure is increased—for example, during coughing.
One way to treat urinary stress incontinence is to strengthen and tighten the muscles that support the pelvic viscera. This is accomplished by Kegel exercises, the alternate contraction and relaxation of muscles of the pelvic floor. To find the correct muscles, the person imagines that she is urinating and then contracts the muscles as if stopping in midstream.
- The muscles should be held for a count of three, then relaxed for a count of three.
- This should be done 5–10 times each hour— sitting, standing, and lying down.
- Kegel exercises are also encouraged during pregnancy to strengthen the muscles for delivery.
One of the most common causes of shoulder pain and dysfunction in athletes is known as impingement syndrome, which is sometimes confused with another common complaint, compartment syndrome.
The repetitive movement of the arm over the head that is common in baseball, overhead racquet sports, lifting weights over the head, spiking a volleyball, and swimming puts these athletes at risk. Impingement syndrome may also be caused by a direct blow or stretch injury.
Continual pinching of the supraspinatus tendon as a result of overhead motions causes it to become inflamed and results in pain. If movement is continued despite the pain, the tendon may degenerate near the attachment to the humerus and ultimately may tear away from the bone (rotator cuff injury).
Treatment consists of resting the injured tendons, strengthening the shoulder through exercise, massage therapy,and surgery if the injury is particularly severe. During surgery, an inflamed bursa may be removed, bone may be trimmed, and/or the coracoacromial ligament may be detached. Torn rotator cuff tendons may be trimmed and then reattached with sutures, anchors, or surgical tacks. These steps make more space, thus relieving pressure and allowing the arm to move freely.
Carpal Tunnel Syndrome
The carpal tunnel is a narrow passageway formed anteriorly by the flexor retinaculum and posteriorly by the carpal bones. Through this tunnel pass the median nerve, the most superficial structure, and the long flexor tendons for the digits.
Structures within the carpal tunnel, especially the median nerve, are vulnerable to compression, and the resulting condition is called carpal tunnel syndrome. Compression of the median nerve leads to sensory changes over the lateral side of the hand and muscle weakness in the thenar eminence.
This results in pain, numbness, and tingling of the fingers. The condition may be caused by
- inflammation of the digital tendon sheaths,
- fluid retention,
- excessive exercise,
- and/or repetitive activities that involve flexion of the wrist, such as keyboarding, cutting hair, or playing the piano.
Treatment may involve the use of nonsteroidal anti-inflammatory drugs (such as ibuprofen or aspirin), wearing a wrist splint, corticosteroid injections, or surgery to cut the flexor retinaculum and release pressure on the median nerve.
Back Injuries and Heavy Lifting
The four factors associated with increased risk of back injury are
- amount of force,
- and stress applied to the backbone.
Poor physical condition, poor posture, lack of exercise, and excessive body weight contribute to the number and severity of sprains and strains.
Back pain caused by a muscle strain or ligament sprain will normally heal within a short time and may never cause further problems. However, if ligaments and muscles are weak, discs in the lower back can become weakened and may herniate (rupture) with excessive lifting or a sudden fall, causing considerable pain.
Full flexion at the waist, as in touching your toes, overstretches the erector spinae muscles. Muscles that are overstretched cannot contract effectively. Straightening up from such a position is therefore initiated by the hamstring muscles on the back of the thigh and the gluteus maximus muscles of the buttocks.
The erector spinae muscles join in as the degree of flexion decreases. Improperly lifting a heavy weight, however, can strain the erector spinae muscles. The result can be painful muscle spasms, tearing of tendons and ligaments of the lower back, and herniating of intervertebral discs. The lumbar muscles are adapted for maintaining posture, not for lifting. This is why it is important to bend at the knees and use the powerful extensor muscles of the thighs and buttocks while lifting a heavy load.
The five major muscles of the inner thigh function to move the legs medially. This muscle group is important in activities such as sprinting, hurdling, and horseback riding.
A rupture or tear of one or more of these muscles can cause a groin pull. Groin pulls most often occur during sprinting or twisting, or from kicking a solid, perhaps stationary object.
Symptoms of a groin pull may be sudden or may not surface until the day after the injury; they include sharp pain in the inguinal region, swelling, bruising, or inability to contract the muscles. As with most strain injuries, treatment involves PRICE therapy, which stands for
- and elevation.
After the injured part is protected from further damage, ice should be applied immediately, and the injured part should be elevated and rested. An elastic bandage should be applied, if possible, to compress the injured tissue.
A strain or partial tear of the proximal hamstring muscles is referred to as pulled hamstrings or hamstring strains. Like pulled groins, they are common sports injuries in individuals who run very hard and/or are required to perform quick starts and stops.
Sometimes the violent muscular exertion required to perform a feat tears away a part of the tendinous origins of the hamstrings, especially the biceps femoris, from the ischial tuberosity.
This is usually accompanied by a contusion (bruising), tearing of some of the muscle fibers, and rupture of blood vessels, producing a hematoma (collection of blood) and sharp pain.
Adequate training with good balance between the quadriceps femoris and hamstrings and stretching exercises before running or competing are important in preventing this injury.
Shin Splint Syndrome
Shin splint syndrome, or simply shin splints, refers to pain or soreness along the tibia, specifically the medial, distal two thirds.
It may be caused by tendinitis of the anterior compartment muscles, especially the tibialis anterior muscle, inflammation of the periosteum (periostitis) around the tibia, or stress fractures of the tibia. The tendinitis usually occurs when poorly conditioned runners run on hard or banked surfaces with poorly supportive running shoes. The condition may also occur with vigorous activity of the legs following a period of relative inactivity or running in cold weather without proper warmup.
The muscles in the anterior compartment (mainly the tibialis anterior) can be strengthened to balance the stronger posterior compartment muscles.
Neurotoxins and Local Anesthetics
Certain shellfish and other organisms contain neurotoxins, substances that produce their poisonous effects by acting on the nervous system. One particularly lethal neurotoxin is tetrodotoxin (TTX), present in the viscera of Japanese puffer fish. TTX effectively blocks action potentials by inserting itself into voltage-gated Na channels so they cannot open.
Local anesthetics are drugs that block pain and other somatic sensations. Examples include procaine (Novocaine®) and lidocaine, which may be used to produce anesthesia in the skin during suturing of a gash, in the mouth during dental work, or in the lower body during childbirth.
Like TTX, these drugs act by blocking the opening of voltage-gated Na channels. Action potentials cannot propagate past the obstructed region, so pain signals do not reach the CNS. Localized cooling of a nerve can also produce an anesthetic effect because axons propagate action potentials at lower speeds when cooled. The application of ice to injured tissue can reduce pain because propagation of the pain sensations along axons is partially blocked.
The importance of inhibitory neurons can be appreciated by observing what happens when their activity is blocked.
Normally, inhibitory neurons in the spinal cord called Renshaw cells release the neurotransmitter glycine at inhibitory synapses with somatic motor neurons. This inhibitory input to their motor neurons prevents excessive contraction of skeletal muscles.
Strychnine is a lethal poison that is mainly used as a pesticide to control rats, moles, gophers, and coyotes. When ingested, it binds to and blocks glycine receptors. The normal, delicate balance between excitation and inhibition in the CNS is disturbed, and motor neurons generate nerve impulses without restraint. All skeletal muscles, including the diaphragm, contract fully and remain contracted.
Because the diaphragm cannot relax, the victim cannot inhale, and suffocation results.
Modifying the Effects of Neurotransmitters
Substances naturally present in the body as well as drugs and toxins can modify the effects of neurotransmitters in
- Neurotransmitter synthesis can be stimulated or inhibited. For instance, many patients with Parkinson’s disease receive benefit from the drug L-dopa because it is a precursor of dopamine. For a limited period of time, taking L-dopa boosts dopamine production in affected brain areas.
- Neurotransmitter release can be enhanced or blocked. Amphetamines promote release of dopamine and norepinephrine. Botulinum toxin causes paralysis by blocking release of acetylcholine from somatic motor neurons.
- The neurotransmitter receptors can be activated or blocked. An agent that binds to receptors and enhances or mimics the effect of a natural neurotransmitter is an agonist. Isoproterenol (Isuprel®) is a powerful agonist of epinephrine and norepinephrine. It can be used to dilate the airways during an asthma attack.
- An agent that binds to and blocks neurotransmitter receptors is an antagonist. Zyprexa®, a drug prescribed for schizophrenia, is an antagonist of serotonin and dopamine.
- Neurotransmitter removal can be stimulated or inhibited. For example, cocaine produces euphoria—intensely pleasurable feelings— by blocking transporters for dopamine re-uptake. This action allows dopamine to linger longer in synaptic clefts, producing excessive stimulation of certain brain regions.
THE SPINAL CORD AND SPINAL NERVES
In a spinal tap (lumbar puncture), a local anesthetic is given, and a long hollow needle is inserted into the subarachnoid space to withdraw cerebrospinal fluid (CSF) for diagnostic purposes;
- to introduce antibiotics,
- contrast media for myelography,
- or anesthetics;
- to administer chemotherapy;
- to measure CSF pressure;
- and/or to evaluate the effects of treatment for diseases such as meningitis.
During this procedure, the patient lies on his or her side with the vertebral column flexed. Flexion of the vertebral column increases the distance between the spinous processes of the vertebrae, which allows easy access to the subarachnoid space.
- The spinal cord ends around the second lumbar vertebra (L2);
- however, the spinal meninges and circulating cerebrospinal fluid extend to the second sacral vertebra (S2).
- Between vertebrae L2 and S2 the spinal meninges are present, but the spinal cord is absent.
Consequently, a spinal tap is normally performed in adults between the L3 and L4 or L4 and L5 lumbar vertebrae because this region provides safe access to the subarachnoid space without the risk of damaging the spinal cord. (A line drawn across the highest points of the iliac crests, called the supracristal line, passes through the spinous process of the fourth lumbar vertebra and is used as a landmark for administering a spinal tap.)
Injuries to the Phrenic Nerves
The phrenic nerves originate from C3, C4, and C5 and supply the diaphragm. Complete severing of the spinal cord above the origin of the phrenic nerves (C3, C4, and C5) causes respiratory arrest. In injuries to the phrenic nerves, breathing stops because the phrenic nerves no longer send nerve impulses to the diaphragm.
The phrenic nerves may also be damaged due to pressure from malignant tracheal or esophageal tumors in the mediastinum.
Injuries to Nerves Emerging from the Brachial Plexus
Injury to the superior roots of the brachial plexus (C5–C6) may result from forceful pulling away of the head from the shoulder, as might occur from a heavy fall on the shoulder or excessive stretching of an infant’s neck during childbirth.
The presentation of this injury is characterized by an upper limb in which the
- shoulder is adducted,
- the arm is medially rotated,
- the elbow is extended,
- the forearm is pronated,
- and the wrist is flexed.
This condition is called Erb-Duchenne palsy or waiter’s tip position. There is loss of sensation along the lateral side of the arm.
Injury to the radial (and axillary) nerve can be caused by improperly administered intramuscular injections into the deltoid muscle. The radial nerve may also be injured when a cast is applied too tightly around the mid-humerus. Radial nerve injury is indicated by
- wrist drop,
- the inability to extend the wrist and fingers
Sensory loss is minimal due to the overlap of sensory innervation by adjacent nerves.
Injuries to the Lumbar Plexus
The largest nerve arising from the lumbar plexus is the femoral nerve. Injuries to the femoral nerve, which can occur in stab or gunshot wounds, are indicated by an inability to extend the leg and by loss of sensation in the skin over the anteromedial aspect of the thigh.
Injuries to the obturator nerve result in paralysis of the adductor muscles of the thigh and loss of sensation over the medial aspect of the thigh. It may result from pressure on the nerve by the fetal head during pregnancy.
Injury to the Sciatic Nerve
The most common form of back pain is caused by compression or irritation of the sciatic nerve, the longest nerve in the human body. The sciatic nerve is actually two nerves—tibial and common fibular—bound together by a common sheath of connective tissue. It splits into its two divisions, usually at the knee.
Injury to the sciatic nerve results in sciatica, pain that may extend from the buttock down the posterior and lateral aspect of the leg and the lateral aspect of the foot.
The sciatic nerve may be injured because of
- a herniated (slipped) disc,
- dislocated hip,
- osteoarthritis of the lumbosacral spine,
- pathological shortening of the lateral rotator muscles of the thigh (especially piriformis),
- pressure from the uterus during pregnancy,
- or an improperly administered gluteal intramuscular injection.
In addition, sitting on a wallet or other object for a long period of time can compress the nerve and induce pain.
In many sciatic nerve injuries, the common fibular portion is the most affected, frequently from fractures of the fibula or by pressure from casts or splints over the thigh or leg.
Damage to the common fibular nerve causes the foot to be plantar flexed, a condition called foot drop. There is also loss of function along the anterolateral aspects of the leg and dorsum of the foot and toes.
Injury to the tibial portion of the sciatic nerve results in dorsiflexion of the foot. Loss of sensation on the sole also occurs.
Treatments for sciatica are similar to those for a herniated (slipped) disc—rest, pain medications, exercises, ice or heat, and massage.
Reflexes and Diagnosis
Reflexes are often used for diagnosing disorders of the nervous system and locating injured tissue. If a reflex ceases to function or functions abnormally, the physician may suspect that the damage lies somewhere along a particular conduction pathway.
Many somatic reflexes can be tested simply by tapping or stroking the body. Among the somatic reflexes of clinical significance are the following:
- Patellar reflex (knee jerk). This stretch reflex involves extension of the leg at the knee joint by contraction of the quadriceps femoris muscle in response to tapping the patellar ligament. This reflex is blocked by damage to the sensory or motor nerves supplying the muscle or to the integrating centers in the second, third, or fourth lumbar segments of the spinal cord.
- It is often absent in people with chronic diabetes mellitus or neurosyphilis, both of which cause degeneration of nerves. It is exaggerated in disease or injury involving certain motor tracts descending from the higher centers of the brain to the spinal cord.
- Achilles reflex(ankle jerk). This stretch reflex involves plantar flexion of the foot in response to tapping the calcaneal (Achilles) tendon. Absence of the Achilles reflex indicates damage to the nerves supplying the posterior leg muscles or to neurons in the lumbosacral region of the spinal cord.
- This reflex may also disappear in people with chronic diabetes, neurosyphilis, alcoholism, and subarachnoid hemorrhages.
- An exaggerated Achilles reflex indicates cervical cord compression or a lesion of the motor tracts of the first or second sacral segments of the cord.
- Babinski sign. This reflex results from gentle stroking of the lateral outer margin of the sole. The great toe extends, with or without a lateral fanning of the other toes. This phenomenon normally occurs in children under 1 & 1∕2 years of age and is due to incomplete myelination of fibers in the corticospinal tract.
- A positive Babinski sign after age 11∕2 is abnormal and indicates an interruption of the corticospinal tract as the result of a lesion of the tract, usually in the upper portion.
The normal response after age 11∕2 is the plantar flexion reflex, or negative Babinski—a curling under of all the toes.
- Abdominal reflex. This reflex involves contraction of the muscles that compress the abdominal wall in response to stroking the side of the abdomen. The response is an abdominal muscle contraction that causes the umbilicus to move in the direction of the stimulus.
- Absence of this reflex is associated with lesions of the corticospinal tracts. It may also be absent because of lesions of the peripheral nerves, lesions of integrating centers in the thoracic part of the cord, or multiple sclerosis.
Most autonomic reflexes are not practical diagnostic tools because it is difficult to stimulate visceral effectors, which are deep inside the body. An exception is the pupillary light reflex, in which the pupils of both eyes decrease in diameter when either eye is exposed to light. Because the reflex arc includes synapses in lower parts of the brain,
the absence of a normal pupillary light reflex may indicate brain damage or injury.
THE BRAIN AND CRANIAL NERVES
Breaching the Blood– Brain Barrier
Because it is so effective, the blood–brain barrier prevents the passage of helpful substances as well as those that are potentially harmful. Researchers are exploring ways to move drugs that could be therapeutic for brain cancer or other CNS disorders past the BBB.
In one method, the drug is injected in a concentrated sugar solution. The high osmotic pressure of the sugar solution causes the endothelial cells of the capillaries to shrink, which opens gaps between their tight junctions, making the BBB more leaky and allowing the drug to enter the brain tissue.
Abnormalities in the brain,tumors,inflammation,or developmental malformations can interfere with the circulation of CSF from the ventricles into the subarachnoid space. When excess CSF accumulates in the ventricles, the CSF pressure rises. Elevated CSF pressure causes a condition called hydrocephalus.
The abnormal accumulation of CSF may be due to an obstruction to CSF flow or an abnormal rate of CSF production and/or reabsorption. In a baby whose fontanels have not yet closed, the head bulges due to the increased pressure.
If the condition persists, the fluid buildup compresses and damages the delicate nervous tissue.
Hydrocephalus is relieved by draining the excess CSF. In one procedure, called endoscopic third ventriculostomy (ETV), a neurosurgeon makes a hole in the floor of the third ventricle and the CSF drains directly into the subarachnoid space.
In adults, hydrocephalus may occur after head injury, meningitis, or subarachnoid hemorrhage. Because the adult skull bones are fused together, this condition can quickly become life-threatening and requires immediate intervention.
Injury to the Medulla
Given the vital activities controlled by the medulla, it is not surprising that injury to the medulla from a hard blow to the back of the head or upper neck such as falling back on ice can be fatal. Damage to the medullary respiratory center is particularly serious and can rapidly lead to death.
Symptoms of nonfatal injury to the medulla may include cranial nerve malfunctions on the same side of the body as the injury, paralysis and loss of sensation on the opposite side of the body, and irregularities in breathing or heart rhythm. Alcohol overdose also suppresses the medullary rhythmicity center and may result in death.
Damage to the cerebellum can result in a loss of ability to coordinate muscular movements, a condition called ataxia. Blindfolded people with ataxia cannot touch the tip of their nose with a finger because they cannot coordinate movement with their sense of where a body part is located.
Another sign of ataxia is a changed speech pattern due to uncoordinated speech muscles. Cerebellar damage may also result in staggering or abnormal walking movements. People who consume too much alcohol show signs of ataxia because alcohol inhibits activity of the cerebellum. Such individuals have difficulty in passing sobriety tests.
Ataxia can also occur as a result of degenerative diseases (multiple sclerosis and Parkinson’s disease), trauma, brain tumors, and genetic factors, and as a side effect of medication prescribed for bipolar disorder.
Much of what we know about language areas comes from studies of patients with language or speech disturbances that have resulted from brain damage. Broca’s speech area, Wernicke’s (posterior language) area, and other language areas are located in the left cerebral hemisphere of most people, regardless of whether they are left-handed or right-handed.
Injury to language areas of the cerebral cortex results in aphasia, an inability to use or comprehend words.
Damage to Broca’s speech area results in nonfluent aphasia, an inability to properly articulate or form words; people with nonfluent aphasia know what they wish to say but cannot speak.
Damage to Wernicke’s area, the common integrative area, or auditory association area results in fluent aphasia, characterized by faulty understanding of spoken or written words. A person experiencing this type of aphasia may fluently produce strings of words that have no meaning (“word salad”). For example, someone with fluent aphasia might say, “I rang car porch dinner light river pencil.” The underlying deficit may be word deafness (an inability to understand spoken words), word blindness (an inability to understand written words), or both.
Brain injuries are commonly associated with head trauma and result in part from displacement and distortion of neural tissue at the moment of impact.
Additional tissue damage may occur when normal blood flow is restored after a period of ischemia (reduced blood flow). The sudden increase in oxygen level produces large numbers of oxygen free radicals (charged oxygen molecules with an unpaired electron). Brain cells recovering from the effects of a stroke or cardiac arrest also release free radicals. Free radicals cause damage by disrupting cellular DNA and enzymes and by altering plasma membrane permeability.
Brain injuries can also result from hypoxia (cellular oxygen deficiency).
A concussion is an injury characterized by an abrupt, but temporary, loss of consciousness (from seconds to hours), disturbances of vision, and problems with equilibrium. It is caused by a blow to the head or the sudden stopping of a moving head (as in an automobile accident) and is the most common brain injury. A concussion produces no obvious bruising of the brain.
Signs of a concussion are
- and/or vomiting,
- lack of concentration,
- or post-traumatic amnesia (memory loss).
A brain contusion is bruising due to trauma and includes the leakage of blood from microscopic vessels. It is usually associated with a concussion. In a contusion, the pia mater may be torn, allowing blood to enter the subarachnoid space. The area most commonly affected is the frontal lobe.
A contusion usually results in an immediate loss of consciousness (generally lasting no longer than 5 minutes), loss of reflexes, transient cessation of respiration, and decreased blood pressure. Vital signs typically stabilize in a few seconds.
A laceration is a tear of the brain, usually from a skull fracture or a gunshot wound. A laceration results in rupture of large blood vessels, with bleeding into the brain and subarachnoid space.
Consequences include cerebral hematoma (localized pool of blood, usually clotted, that swells against the brain tissue), edema, and increased intracranial pressure. If the blood clot is small enough, it may pose no major threat and may be absorbed. If the blood clot is large, it may require surgical removal.
Swelling infringes on the limited space that the brain occupies in the cranial cavity. Swelling causes excruciating headaches. Brain tissue can also undergo necrosis (cellular death) due to the swelling; if the swelling is severe enough, the brain can herniate through the foramen magnum, resulting in death.
The inferior alveolar nerve, a branch of the mandibular nerve, supplies all of the teeth in one half of the mandible; it is often anesthetized in dental procedures. The same procedure will anesthetize the lower lip because the mental nerve is a branch of the inferior alveolar nerve. Because the lingual nerve runs very close to the inferior alveolar nerve near the mental foramen, it too is often anesthetized at the same time.
For anesthesia to the upper teeth, the superior alveolar nerve endings, which are branches of the maxillary nerve, are blocked by inserting the needle beneath the mucous membrane. The anesthetic solution is then infiltrated slowly throughout the area of the roots of the teeth to be treated.
Loss of the sense of smell, called anosmia (an-OZ-me¯-a), may result from
- infections of the nasal mucosa,
- head injuries in which the cribriform plate of the ethmoid bone is fractured,
- lesions along the olfactory pathway or in the brain, meningitis, smoking, or cocaine use.
Fractures in the orbit, brain lesions, damage along the visual pathway, diseases of the nervous system (such as multiple sclerosis), pituitary gland tumors, or cerebral aneurysms (enlargements of blood vessels due to weakening of their walls) may result in visual field defects and loss of visual acuity. Blindness due to a defect in or loss of one or both eyes is called anopia (an-O¯ -pe¯-a).
Strabismus, Ptosis, and Diplopia
Damage to the oculomotor (III) nerve causes
- strabismus (stra-BIZ-mus) (a condition in which both eyes do not fix on the same object, since one or both eyes may turn inward or outward),
- ptosis (TO¯ -sis) (drooping) of the upper eyelid, dilation of the pupil, movement of the eyeball downward and outward on the damaged side, loss of accommodation for near vision,
- and diplopia (di-PLO¯ -pe¯-a) (double vision).
Trochlear (IV) nerve damage can also result in strabismus and diplopia.
With damage to the abducens (VI) nerve, the affected eyeball cannot move laterally beyond the midpoint, and the eyeball usually is directed medially. This leads to strabismus and diplopia.
Causes of damage to the oculomotor, trochlear, and abducens nerves include trauma to the skull or brain, compression resulting from aneurysms, and lesions of the superior orbital fissure.
Individuals with damage to these nerves are forced to tilt their heads in various directions to help bring the affected eyeball into the correct frontal plane.
Neuralgia (pain) relayed via one or more branches of the trigeminal (V) nerve, caused by conditions such as inflammation or lesions, is called trigeminal neuralgia (tic douloureux).
This is a sharp cutting or tearing pain that lasts for a few seconds to a minute and is caused by anything that presses on the trigeminal nerve or its branches. It occurs almost exclusively in people over 60 and can be the first sign of a disease, such as
- multiple sclerosis
- or diabetes,
- or lack of vitamin B12,
which damage the nerves.
Injury of the mandibular nerve may cause paralysis of the chewing muscles and a loss of the sensations of touch, temperature, and proprioception in the lower part of the face.
Damage to the facial (VII) nerve due to conditions such as viral infection (shingles) or a bacterial infection (Lyme disease) produces Bell’s palsy (paralysis of the facial muscles), loss of taste, decreased salivation, and loss of ability to close the eyes, even during sleep. The nerve can also be damaged by trauma, tumors, and stroke.
Vertigo, Ataxia, Nystagmus, and Tinnitus
Injury to the vestibular branch of the vestibulocochlear (VIII) nerve may cause
- vertigo (ver-TI-go¯) (a subjective feeling that one’s own body or the environment is rotating),
- ataxia (a-TAK-se¯-a) (muscular incoordination),
- and nystagmus (nis-TAG-mus) (involuntary rapid movement of the eyeball).
Injury to the cochlear branch may cause tinnitus (ringing in the ears) or deafness. The vestibulocochlear nerve may be injured as a result of conditions such as trauma, lesions, or middle ear infections.
Dysphagia, Aptyalia, and Ageusia
Injury to the glossopharyngeal (IX) nerve causes
- dysphagia (dis-FA¯-ge¯-a), or difficulty in swallowing;
- aptyalia (ap-te¯-A¯ -le¯-a), or reduced secretion of saliva; loss of sensation in the throat;
- and ageusia (a-GOO-se¯-a), or loss of taste sensation.
The glossopharyngeal nerve may be injured as a result of conditions such as trauma or lesions.
The pharyngeal (gag) reflex is a rapid and intense contraction of the pharyngeal muscles. Except for normal swallowing, the pharyngeal reflex is designed to prevent choking by not allowing objects to enter the throat. The reflex is initiated by contact of an object with the roof of the mouth, back of the tongue, area around the tonsils, and back of the throat.
Stimulation of receptors in these areas sends sensory information to the brain via the glossopharyngeal (IX) and vagus (X) nerves. Returning motor information via the same nerves results in contraction of the pharyngeal muscles. People with a hyperactive pharyngeal reflex have difficulty swallowing pills and are very sensitive to various medical and dental procedures.
Vagal Neuropathy, Dysphagia, and Tachycardia
Injury to the vagus (X) nerve due to conditions such as trauma or lesions causes
- vagal neuropathy, or interruptions of sensations from many organs in the thoracic and abdominal cavities;
- dysphagia (dis-FA¯-ge¯-a), or difficulty in swallowing;
- and tachycardia (tak’-i-KARde ¯-a), or increased heart rate.
Paralysis of the Sternocleidomastoid and Trapezius Muscles
If the accessory (XI) nerve is damaged due to conditions such as trauma, lesions, or stroke, the result is paralysis of the
sternocleidomastoid and trapezius muscles so that the person is unable to raise the shoulders and has difficulty in turning the head.
Dysarthria and Dysphagia
Injury to the hypoglossal (XII) nerve results in
- difficulty in chewing; dysarthria (dis-AR-thre¯-a),
- or difficulty in speaking; and dysphagia (dis-FA¯ -ge¯-a), or difficulty in swallowing.
The tongue, when protruded, curls toward the affected side, and the affected side atrophies. The hypoglossal nerve may be injured as a result of conditions such as trauma, lesions, stroke, amyotrophic lateral sclerosis (Lou Gehrig’s disease), or infections in the brain stem.
THE AUTONOMIC NERVOUS SYSTEM
In Horner’s syndrome, the sympathetic innervation to one side of the face is lost due to
- an inherited mutation,
- an injury,
- or a disease that affects sympathetic outflow through the superior cervical ganglion.
Symptoms occur on the affected side and include ptosis (drooping of the upper eyelid), miosis (constricted pupil), and anhidrosis (lack of sweating).
SENSORY, MOTOR, AND INTEGRATIVE SYSTEMS
Phantom Limb Sensation
Patients who have had a limb amputated may still experience sensations such as itching, pressure, tingling, or pain as if the limb were still there.
This phenomenon is called phantom limb sensation. Although the limb has been removed, severed endings of sensory axons are still present in the remaining stump. If these severed endings are activated, the cerebral cortex interprets the sensation as coming from the sensory receptors in the nonexisting (phantom) limb.
Another explanation for phantom limb sensation is that the area of the cerebral cortex that previously received sensory input from the missing limb undergoes extensive functional reorganization that allows it to respond to stimuli from another body part. The remodeling of this cortical area is thought to give rise to false sensory perceptions from the missing limb.
Phantom limb pain can be very distressing to an amputee. Many report that the pain is severe or extremely intense, and that it often does not respond to traditional pain medication therapy. In such cases, alternative treatments may include electrical nerve stimulation, acupuncture, and biofeedback.
Analgesia: Relief from Pain
Pain sensations sometimes occur out of proportion to minor damage, persist chronically due to an injury, or even appear for no obvious reason. In such cases, analgesia or pain relief is needed.
Analgesic drugs such as aspirin and ibuprofen block formation of prostaglandins, which stimulate nociceptors. Local anesthetics, provide short-term pain relief by blocking conduction of nerve impulses along the axons of first-order pain neurons.
Morphine and other opiate drugs alter the quality of pain perception in the brain; pain is still sensed but it is no longer perceived as being so noxious. Many pain clinics use anticonvulsant and antidepressant medications to treat those suffering from chronic pain.
Syphilis is a sexually transmitted disease caused by the bacterium Treponema pallidum. Because it is a bacterial infection, it can be treated with antibiotics.
However, if the infection is not treated, the third stage of syphilis typically causes debilitating neurological symptoms. A common outcome is progressive degeneration of the posterior portions of the spinal cord, including the posterior columns, posterior spinocerebellar tracts, and posterior roots.
Somatic sensations are lost, and the person’s gait becomes uncoordinated and jerky because proprioceptive impulses fail to reach the cerebellum.
Damage or disease of lower motor neurons produces flaccid paralysis of muscles on the same side of the body. There is neither voluntary nor reflex action of the innervated muscle fibers, muscle tone is decreased or lost, and the muscle remains limp or flaccid.
Injury or disease of upper motor neurons in the cerebral cortex removes inhibitory influences that some of these neurons have on lower motor neurons, which causes spastic paralysis of muscles on the opposite side of the body. In this condition muscle tone is increased, reflexes are exaggerated, and pathological reflexes such as the Babinski sign appear.
Amyotrophic Lateral Sclerosis
Amyotrophic lateral sclerosis (ALS) is a progressive degenerative disease that attacks motor areas of the cerebral cortex, axons of upper motor neurons in the lateral white columns (corticospinal and rubrospinal tracts), and lower motor neuron cell bodies.
It causes progressive muscle weakness and atrophy. ALS often begins in sections of the spinal cord that serve the hands and arms but rapidly spreads to involve the whole body and face, without affecting intellect or sensations. Death typically occurs in 2 to 5 years.
ALS is commonly known as Lou Gehrig’s disease after the New York Yankees baseball player who died from it at age 37 in 1941.
The drug riluzole, which is used to treat ALS, reduces damage to motor neurons by decreasing the release of glutamate. In addition to riluzole, ALS is treated with drugs that relieve symptoms such as fatigue, muscle pain and spasticity, excessive saliva, and difficulty sleeping.
The only other treatment is supportive care provided by physical, occupational, and speech therapists; nutritionists; social workers; and home care and hospice nurses.
Disorders of the Basal Nuclei
Disorders of the basal nuclei can affect
- body movements, cognition, and behavior.
Uncontrollable shaking (tremor) and muscle rigidity (stiffness) are hallmark signs of Parkinson’s disease (PD). In this disorder, dopamine-releasing neurons that extend from the substantia nigra to the putamen and caudate nucleus degenerate.
Huntington disease (HD) is an inherited disorder in which the caudate nucleus and putamen degenerate, with loss of neurons that normally release GABA or acetylcholine.
A key sign of HD is
- chorea, in which rapid, jerky movements occur involuntarily and without purpose.
- Progressive mental deterioration also occurs.
- Symptoms of HD often do not appear until age 30 or 40. Death occurs 10 to 20 years after symptoms first appear.
Tourette syndrome is a disorder that is characterized by
- involuntary body movements (motor tics)
- and the use of inappropriate or unnecessary sounds or words (vocal tics).
Although the cause is unknown, research suggests that this disorder involves a dysfunction of the cognitive neural circuits between the basal nuclei and the prefrontal cortex.
Some psychiatric disorders, such as schizophrenia and obsessive compulsive disorder, are thought to involve dysfunction of the behavioral neural circuits between the basal nuclei and the limbic system.
In schizophrenia, excess dopamine activity in the brain causes a person to experience delusions, distortions of reality, paranoia, and hallucinations.
People who have obsessive–compulsive disorder (OCD) experience repetitive thoughts (obsessions) that cause repetitive behaviors (compulsions) that they feel obligated to perform. For example, a person with OCD might have repetitive thoughts about someone breaking into the house; these thoughts might drive that person to check the doors of the house over and over again (for minutes or hours at a time) to make sure that they are locked.
Common sleep disorders include insomnia, sleep apnea, and narcolepsy.
- A person with insomnia has difficulty in falling asleep or staying asleep. Possible causes of insomnia include stress, excessive caffeine intake, disruption of circadian rhythms (for example, working the night shift instead of the day shift at your job), and depression.
- Sleep apnea is a disorder in which a person repeatedly stops breathing for 10 or more seconds while sleeping.
Most often, it occurs because a loss of muscle tone in pharyngeal muscles allows the airway to collapse.
- Narcolepsy is a condition in which REM sleep cannot be inhibited during waking periods. As a result, involuntary periods of sleep that last about 15 minutes occur throughout the day. Recent studies have revealed that people with narcolepsy have a deficiency of the neuropeptide orexin, which is also known as hypocretin. Orexin is released from certain neurons of the hypothalamus and has a role in promoting wakefulness.
Amnesia refers to the lack or loss of memory. It is a total or partial inability to remember past experiences.
- In anterograde amnesia, there is memory loss for events that occur after the trauma or disease that caused the condition. In other words, it is an inability to form new memories.
- In retrograde amnesia, there is a memory loss for events that occurred before the trauma or disease that caused the condition. In other words, it is an inability to recall past events.
THE SPECIAL SENSES
Women often have a keener sense of smell than men do, especially at the time of ovulation. Smoking seriously impairs the sense of smell in the short term and may cause long-term damage to olfactory receptors. With aging the sense of smell deteriorates. Hyposmia, a reduced ability to smell, affects half of those over age 65 and 75% of those over age 80.
Hyposmia also can be caused by
- neurological changes,
- such as a head injury,
- Alzheimer’s disease,
- or Parkinson’s disease;
- certain drugs, such as antihistamines, analgesics, or steroids;
- and the damaging effects of smoking.
Probably because of taste projections to the hypothalamus and limbic system, there is a strong link between taste and pleasant or unpleasant emotions.
- Sweet foods evoke reactions of pleasure
- while bitter ones cause expressions of disgust, even in newborn babies.
This phenomenon is the basis for taste aversion, in which people and animals quickly learn to avoid a food if it upsets the digestive system. The advantage of avoiding foods that cause such illness is longer survival. However, the drugs and radiation treatments used to combat cancer often cause nausea and gastrointestinal upset regardless of what foods are consumed. Thus, cancer patients may lose their appetite because they develop taste aversions for most foods.
A detached retina may occur due to trauma, such as a blow to the head, in various eye disorders, or as a result of age related degeneration.
The detachment occurs between the neural portion of the retina and the pigmented epithelium. Fluid accumulates between these layers, forcing the thin, pliable retina to billow outward. The result is distorted vision and blindness in the corresponding field of vision.
The retina may be reattached by laser surgery or cryosurgery (localized application of extreme cold), and reattachment must be accomplished quickly to avoid permanent damage to the retina.
An increasingly popular alternative to wearing glasses or contact lenses is refractive surgery to correct the curvature of the cornea for conditions such as
- and astigmatism.
The most common type of refractive surgery is LASIK (laser-assisted in-situ keratomileusis).
After anesthetic drops are placed in the eye, a circular flap of tissue from the center of the cornea is cut. The flap is folded out of the way, and the underlying layer of cornea is reshaped with a laser, one microscopic layer at a time. A computer assists the physician in removing very precise layers of the cornea. After the sculpting is complete, the corneal flap is re-positioned over the treated area. A patch is placed over the eye overnight and the flap quickly reattaches to the rest of the cornea.
Color Blindness and Night Blindness
Most forms of color blindness, an inherited inability to distinguish between certain colors, result from the absence or deficiency of one of the three types of cones.
The most common type is red–green color blindness, in which red cones or green cones are missing. As a result, the person cannot distinguish between red and green.
Prolonged vitamin A deficiency and the resulting below-normal amount of rhodopsin may cause night blindness, an inability to see well at low light levels.
Motion sickness is a condition that results when there is a conflict among the senses with regard to motion. For example, the vestibular apparatus senses angular and vertical motion, while the eyes and proprioceptors in muscles and joints determine the position of the body in space.
If you are in the cabin of a moving ship, your vestibular apparatus informs the brain that there is movement from waves. But your eyes don’t see any movement. This leads to the conflict among the senses. Motion sickness can also be experienced in other situations that involve movement, for example, in a car or airplane or on a train or amusement park ride.
Symptoms of motion sickness include paleness, restlessness, excess salivation, nausea, dizziness, cold sweats, headache, and malaise that may progress to vomiting.
Once the motion is stopped, the symptoms disappear. If it is not possible to stop the motion, you might try sitting in the front seat of a car, the forward car of a train, the upper deck on a boat, or the wing seats in a plane. Looking at the horizon and not reading also help.
THE ENDOCRINE SYSTEM
Blocking Hormone Receptors
Synthetic hormones that block the receptors for some naturally occurring hormones are available as drugs.
For example, RU486, which is used to induce abortion, binds to the receptors for progesterone (a female sex hormone) and prevents progesterone from exerting its normal effect, in this case preparing the lining of the uterus for implantation.
When RU486 is given to a pregnant woman, the uterine conditions needed for nurturing an embryo are not maintained, embryonic development stops, and the embryo is sloughed off along with the uterine lining.
This example illustrates an important endocrine principle:
If a hormone is prevented from interacting with its receptors, the hormone cannot perform its normal functions.
Both steroid hormones and thyroid hormones are effective when taken by mouth. They are not split apart during digestion and easily cross the intestinal lining because they are lipid-soluble.
By contrast, peptide and protein hormones, such as insulin, are not effective oral medications because digestive enzymes destroy them by breaking their peptide bonds. This is why people who need insulin must take it by injection.
Diabetogenic Effect of hGH
One symptom of excess human growth hormone (hGH) is hyperglycemia. Persistent hyperglycemia in turn stimulates the pancreas to secrete insulin continually.
Such excessive stimulation, if it lasts for weeks or months, may cause “beta-cell burnout,” a greatly decreased capacity of pancreatic beta cells to synthesize and secrete insulin. Thus, excess secretion of human growth hormone may have a diabetogenic effect; that is, it causes diabetes mellitus (lack of insulin activity).
Oxytocin and Childbirth
Years before oxytocin was discovered, it was common practice in midwifery to let a first-born twin nurse at the mother’s breast to speed the birth of the second child. Now we know why this practice is helpful—it stimulates the release of oxytocin.Even after a single birth, nursing promotes expulsion of the placenta (afterbirth) and helps the uterus regain its smaller size.
Synthetic oxytocin (Pitocin) often is given to induce labor or to increase uterine tone and control hemorrhage just after giving birth.
Congenital Adrenal Hyperplasia
Congenital adrenal hyperplasia (CAH) is a genetic disorder in which one or more enzymes needed for synthesis of cortisol are absent.
Because the cortisol level is low, secretion of ACTH by the anterior pituitary is high due to lack of negative feedback inhibition. ACTH in turn stimulates growth and secretory activity of the adrenal cortex. As a result, both adrenal glands are enlarged.
However, certain steps leading to synthesis of cortisol are blocked. Thus, precursor molecules accumulate, and some of these are weak androgens that can undergo conversion to testosterone.
The result is virilism or masculinization.
In a female, virile characteristics include growth of a beard, development of a much deeper voice and a masculine distribution of body hair, growth of the clitoris so it may resemble a penis, atrophy of the breasts, and increased muscularity that produces a masculine physique.
In prepubertal males, the syndrome causes the same characteristics as in females, plus rapid development of the male sexual organs and emergence of male sexual desires.
In adult males, the virilizing effects of CAH are usually completely obscured by the normal effects of the testosterone secreted by the testes. As a result, CAH is often difficult to diagnose in adult males.
Treatment involves cortisol therapy, which inhibits ACTH secretion and thus reduces production of adrenal androgens.
THE CARDIOVASCULAR SYSTEM: THE BLOOD
Blood samples for laboratory testing may be obtained inseveral ways.
The most common procedure is venipuncture, withdrawal of blood from a vein using a needle and collecting tube, which contains various additives. A tourniquet is wrapped around the arm above the venipuncture site, which causes blood to accumulate in the vein. This increased blood volume makes the vein stand out. Opening and closing the fist further causes it to stand out, making the venipuncture more successful.
A common site for venipuncture is the median cubital vein anterior to the elbow. Another method of withdrawing blood is through a finger or heel stick. Diabetic patients who monitor their daily blood sugar typically perform a finger stick, and it is often used for drawing blood from infants and children.
In an arterial stick, blood is withdrawn from an artery; this test is used to determine the level of oxygen in oxygenated blood.
Bone Marrow Examination
Sometimes a sample of red bone marrow must be obtained in order to diagnose certain blood disorders, such as leukemia and severe anemias. Bone marrow examination may involve bone marrow aspiration (withdrawal of a small amount of red bone marrow with a fine needle and syringe) or a bone marrow biopsy (removal of a core of red bone marrow with a larger needle).
Both types of samples are usually taken from the iliac crest of the hip bone, although samples are sometimes aspirated from the sternum. In young children, bone marrow samples are taken from a vertebra or tibia (shin bone).
The tissue or cell sample is then sent to a pathology lab for analysis. Specifically, laboratory technicians look for signs of neoplastic (cancer) cells or other diseased cells to assist in diagnosis.
Complete Blood Count
A complete blood count (CBC) is a very valuable test that screens for anemia and various infections.
Usually included are counts of
- RBCs, WBCs, and platelets per microliter of whole blood; hematocrit; and differential white blood cell count.
The amount of hemoglobin in grams per milliliter of blood also is determined.
Normal hemoglobin ranges are as follows:
- infants, 14–20 g/100 mL of blood;
- adult females, 12–16 g/100 mL of blood;
- and adult males, 13.5–18 g/100 mL of blood.
Aspirin and Thrombolytic Agents
In patients with heart and blood vessel disease, the events of hemostasis may occur even without external injury to a blood vessel.
At low doses, aspirin inhibits vasoconstriction and platelet aggregation by blocking synthesis of thromboxane A2. It also reduces the chance of thrombus formation. Due to these effects, aspirin reduces the risk of transient ischemic attacks (TIA), strokes, myocardial infarction, and blockage of peripheral arteries.
Thrombolytic agents are chemical substances that are injected into the body to dissolve blood clots that have already formed to restore circulation. A genetically engineered version of human tissue plasminogen activator (tPA) is now used to treat victims of both heart attacks and brain attacks (strokes) that are caused by blood clots.
Patients who are at increased risk of forming blood clots may receive anticoagulants. Examples are heparin or warfarin.
- Heparin is often administered during hemodialysis and openheart surgery. Warfarin acts as an antagonist to vitamin K and thus blocks synthesis of four clotting factors.
- Warfarin is slower acting than heparin.
THE CARDIOVASCULAR SYSTEM: THE HEART
Cardiopulmonary resuscitation (CPR) refers to an emergency procedure for establishing a normal heartbeat and rate of breathing.
Standard CPR uses a combination of cardiac compression and artificial ventilation of the lungs via mouth-to-mouth respiration and, for many years, this combination was the sole method of CPR. Recently, however, hands-only CPR has become the preferred method.
Because the heart lies between two rigid structures—the sternum and vertebral column—pressure on the chest (compression) can be used to force blood out of the heart and into the circulation. After calling 911, hands-only CPR should be administered. In the procedure, chest compressions should be given hard and fast at a rate of 100 per minute and two inches deep in adults.
Inflammation of the pericardium is called pericarditis.
The most common type, acute pericarditis, begins suddenly and has no known cause in most cases but is sometimes linked to a viral infection. As a result of irritation to the pericardium, there is chest pain that may extend to the left shoulder and down the left arm (often mistaken for a heart attack) and pericardial friction rub (a scratchy or creaking sound heard through a stethoscope as the visceral layer of the serous pericardium rubs against the parietal layer of the serous pericardium). Acute pericarditis usually lasts for about 1 week and is treated with drugs that reduce inflammation and pain, such as ibuprofen or aspirin.
Chronic pericarditis begins gradually and is long-lasting. In one form of this condition, there is a buildup of pericardial fluid. If a great deal of fluid accumulates, this is a life-threatening condition because the fluid compresses the heart, a condition called cardiac tamponade. As a result of the compression,
- ventricular filling is decreased,
- cardiac output is reduced,
- venous return to the heart is diminished,
- blood pressure falls,
- and breathing is difficult.
In most cases, the cause of chronic pericarditis involving cardiac tamponade is unknown, but it sometimes results from conditions such as cancer and tuberculosis. Treatment consists of draining the excess fluid through a needle passed into the pericardial cavity.
Myocarditis and Endocarditis
Myocarditis is an inflammation of the myocardium that usually occurs as
- a complication of a viral infection,
- rheumatic fever,
- or exposure to radiation or certain chemicals or medications.
Myocarditis often has no symptoms. However, if they do occur, they may include fever, fatigue, vague chest pain, irregular or rapid heartbeat, joint pain, and breathlessness. Myocarditis is usually mild and recovery occurs within 2 weeks. Severe cases can lead to cardiac failure and death. Treatment consists of avoiding vigorous exercise, a low-salt diet, electrocardiographic monitoring, and treatment of the cardiac failure.
Endocarditis refers to an inflammation of the endocardium and typically involves the heart valves. Most cases are caused by bacteria (bacterial endocarditis).
Signs and symptoms of endocarditis include fever, heart murmur, irregular or rapid heartbeat, fatigue, loss of appetite, night sweats, and chills. Treatment is with intravenous antibiotics.
Heart Valve Disorders
When heart valves operate normally, they open fully and close completely at the proper times.
- A narrowing of a heart valve opening that restricts blood flow is known as stenosis
- Failure of a valve to close completely is termed insufficiency or incompetence.
In mitral stenosis, scar formation or a congenital defect causes narrowing of the mitral valve.
One cause of mitral insufficiency, in which there is backflow of blood from the left ventricle into the left atrium, is mitral valve prolapse (MVP). In MVP one or both cusps of the mitral valve protrude into the left atrium during ventricular contraction. Mitral valve prolapse is one of the most common valvular disorders, affecting as much as 30% of the population. It is more prevalent in women than in men, and does not always pose a serious threat.
In aortic stenosis the aortic valve is narrowed, and in aortic insufficiency there is backflow of blood from the aorta into the left ventricle.
Certain infectious diseases can damage or destroy the heart valves. One example is rheumatic fever, an acute systemic inflammatory disease that usually occurs after a streptococcal infection of the throat. The bacteria trigger an immune response in which antibodies produced to destroy the bacteria instead attack and inflame the connective tissues in joints, heart valves, and other organs. Even though rheumatic fever may weaken the entire heart wall, most often it damages the mitral and aortic valves.
If daily activities are affected by symptoms and if a heart valve cannot be repaired surgically, then the valve must be replaced. Tissue valves may be provided by human donors or pigs; sometimes, mechanical replacements are used. In any case, valve replacement involves open heart surgery. The aortic valve is the most commonly replaced heart valve.
Myocardial Ischemia and Infarction
Partial obstruction of blood flow in the coronary arteries may cause myocardial ischemia, a condition of reduced blood flow to the myocardium.
Usually, ischemia causes hypoxia (reduced oxygen supply), which may weaken cells without killing them. Angina pectoris, which literally means “strangled chest,” is a severe pain that usually accompanies myocardial ischemia. Typically, sufferers describe it as a tightness or squeezing sensation, as though the chest were in a vise. The pain associated with angina pectoris is often referred to the neck, chin, or down the left arm to the elbow. Silent myocardial ischemia, ischemic episodes without pain, is particularly dangerous because the person has no forewarning of an impending heart attack.
A complete obstruction to blood flow in a coronary artery may result in a myocardial infarction (MI), commonly called a heart attack. Infarction means the death of an area of tissue because of interrupted blood supply. Because the heart tissue distal to the obstruction dies and is replaced by noncontractile scar tissue, the heart muscle loses some of its strength. Depending on the size and location of the infarcted (dead) area, an infarction may disrupt the conduction system of the heart and cause sudden death by triggering ventricular fibrillation.
Treatment for a myocardial infarction may involve
- injection of a thrombolytic (clot-dissolving) agent such as streptokinase or tPA,
- plus heparin (an anticoagulant),
- or performing coronary angioplasty
- or coronary artery bypass grafting.
Fortunately, heart muscle can remain alive in a resting person if it receives as little as 10–15% of its normal blood supply.
Regeneration of Heart Cells
The heart of an individual who survives a heart attack often has regions of infarcted (dead) cardiac muscle tissue that typically are replaced with noncontractile fibrous scar tissue over time.
Our inability to repair damage from a heart attack has been attributed to a lack of stem cells in cardiac muscle and to the absence of mitosis in mature cardiac muscle fibers. A recent study of heart transplant recipients by American and Italian scientists, however, provides evidence for significant replacement of heart cells. The researchers studied men who had received a heart from a female, and then looked for the presence of a Y chromosome in heart cells. (All female cells except gametes have two X chromosomes and lack the Y chromosome.)
Several years after the transplant surgery, between 7% and 16% of the heart cells in the transplanted tissue, including cardiac muscle fibers and endothelial cells in coronary arterioles and capillaries, had been replaced by the recipient’s own cells, as evidenced by the presence of a Y chromosome. The study also revealed cells with some of the characteristics of stem cells in both transplanted hearts and control hearts. Evidently, stem cells can migrate from the blood into the heart and differentiate into functional muscle and endothelial cells. The hope is that researchers can learn how to “turn on” such regeneration of heart cells to treat people with heart failure or cardiomyopathy (diseased heart).
If the SA node becomes damaged or diseased, the slower AV node can pick up the pacemaking task. Its spontaneous pacing rate is 40 to 60 times per minute. If the activity of both nodes is suppressed, the heartbeat may still be maintained by autorhythmic fibers in the ventricles—the AV bundle, a bundle branch, or Purkinjefibers. However, the pacing rate is so slow (20–35 beats per minute) that blood flow to the brain is inadequate.
When this condition occurs, normal heart rhythm can be restored and maintained by surgically implanting an artificial pacemaker, a device that sends out small electrical currents to stimulate the heart to contract. A pacemaker consists of a battery and impulse generator and is usually implanted beneath the skin just inferior to the clavicle. The pacemaker is connected to one or two flexible leads (wires) that are threaded through the superior vena cava and then passed into the various chambers of the heart.
Many of the newer pacemakers, referred to as activity-adjusted pacemakers, automatically speed up the heartbeat
Heart sounds provide valuable information about the mechanical operation of the heart. A heart murmur is an abnormal sound consisting of a clicking, rushing, or gurgling noise that either is heard before, between, or after the normal heart sounds, or may mask the normal heart sounds.
Heart murmurs in children are extremely common and usually do not represent a health condition. Murmurs are most frequently discovered in children between the ages of 2 and 4. These types of heart murmurs are referred to as innocent or functional heart murmurs; they often subside or disappear with growth.
Although some heart murmurs in adults are innocent, most often an adult murmur indicates a valve disorder.
When a heart valve exhibits stenosis, the heart murmur is heard while the valve should be fully open but is not. For example, mitral stenosis produces a murmur during the relaxation period, between S2 and the next S1. An incompetent heart valve, by contrast, causes a murmur to appear when the valve should be fully closed but is not. So, a murmur due to mitral incompetence occurs during ventricular systole, between S1 and S2.
THE CARDIOVASCULAR SYSTEM: BLOOD VESSELS AND HEMODYNAMICS
Angiogenesis and Disease
Angiogenesis refers to the growth of new blood vessels.
It is an important process in embryonic and fetal development, and in postnatal life serves important functions such as wound healing, formation of a new uterine lining after menstruation, formation of the corpus luteum after ovulation, and development of blood vessels around obstructed arteries in the coronary circulation.
Several proteins (peptides) are known to promote and inhibit angiogenesis. Clinically angiogenesis is important because cells of a malignant tumor secrete proteins called tumor angiogenesis factors (TAFs) that stimulate blood vessel growth to provide nourishment for the tumor cells. Scientists are seeking chemicals that would inhibit angiogenesis and thus stop the growth of tumors.
In diabetic retinopathy, angiogenesis may be important in the development of blood vessels that actually cause blindness, so finding inhibitors of angiogenesis may also prevent the blindness associated with diabetes.
If filtration greatly exceeds reabsorption, the result is edema, an abnormal increase in interstitial fluid volume. Edema is not usually detectable in tissues until interstitial fluid volume has risen to 30% above normal. Edema can result from either excess filtration or inadequate reabsorption.
Two situations may cause excess filtration:
- Increased capillary blood pressure causes more fluid to be filtered from capillaries.
- Increased permeability of capillaries raises interstitial fluid osmotic pressure by allowing some plasma proteins to escape. Such leakiness may be caused by the destructive effects of chemical, bacterial, thermal, or mechanical agents on capillary walls.
One situation commonly causes inadequate reabsorption:
- Decreased concentration of plasma proteins lowers the blood colloid osmotic pressure. Inadequate synthesis or dietary intake or loss of plasma proteins is associated with liver disease, burns, malnutrition, and kidney disease.
Syncope, or fainting, is a sudden, temporary loss of consciousness that is not due to head trauma, followed by spontaneous recovery. It is most commonly due to cerebral ischemia, lack of sufficient blood flow to the brain.
Syncope may occur for several reasons:
- Vasodepressor syncope is due to sudden emotional stress or real, threatened, or fantasized injury.
- Situational syncope is caused by pressure stress associated with urination, defecation, or severe coughing.
- Drug-induced syncope may be caused by drugs such as antihypertensives, diuretics, vasodilators, and tranquilizers.
- Orthostatic hypotension, an excessive decrease in blood pressure that occurs on standing up, may cause fainting.
THE LYMPHATIC SYSTEM AND IMMUNITY
Metastasis through Lymphatic Vessels
Metastasis, the spread of a disease from one part of the body to another, can occur via lymphatic vessels. All malignant tumors eventually metastasize. Cancer cells may travel in the blood or lymph and establish new tumors where they lodge.
When metastasis occurs via lymphatic vessels, secondary tumor sites can be predicted according to the direction of lymph flow from the primary tumor site. Cancerous lymph nodes feel enlarged, firm, nontender, and fixed to underlying structures. By contrast, most lymph nodes that are enlarged due to an infection are softer, tender, and movable.
The spleen is the organ most often damaged in cases of abdominal trauma.
Severe blows over the inferior left chest or superior abdomen can fracture the protecting ribs. Such crushing injury may result in a ruptured spleen, which causes significant hemorrhage and shock. Prompt removal of the spleen, called a splenectomy, is needed to prevent death due to bleeding.
Other structures, particularly red bone marrow and the liver, can take over some functions normally carried out by the spleen. Immune functions, however, decrease in the absence of a spleen. The spleen’s absence also places the patient at higher risk for sepsis (a blood infection) due to loss of the filtering and phagocytic functions of the spleen. To reduce the risk of sepsis, patients who have undergone a splenectomy take prophylactic (preventive) antibiotics before any invasive procedures.
Tonsillitis is an infection or inflammation of the tonsils. Most often, it is caused by a virus, but it may also be caused by the same bacteria that cause strep throat.
The principal symptom of tonsillitis is a sore throat. Additionally, fever, swollen lymph nodes, nasal congestion, difficulty in swallowing, and headache may also occur.
- Tonsillitis of viral origin usually resolves on its own.
- Bacterial tonsillitis is typically treated with antibiotics.
Tonsillectomy, the removal of a tonsil, may be indicated for individuals who do not respond to other treatments. Such individuals usually have tonsillitis lasting for more than 3 months (despite medication), obstructed air pathways, and difficulty in swallowing and talking. It appears that tonsillectomy does not interfere with a person’s response to subsequent infections.•
Microbial Evasion of Phagocytosis
Some microbes, such as the bacteria that cause pneumonia, have extracellular structures called capsules that prevent adherence. This makes it physically difficult for phagocytes to engulf the microbes.
Other microbes, such as the toxin-producing bacteria that cause one kind of food poisoning, may be ingested but not killed; instead, the toxins they produce (leukocidins) may kill the phagocytes by causing the release of the phagocyte’s own lysosomal enzymes into its cytoplasm.
Still other microbes—such as the bacteria that cause tuberculosis—inhibit fusion of phagosomes and lysosomes and thus prevent exposure of the microbes to lysosomal enzymes. These bacteria apparently can also use chemicals in their cell walls to counter the effects of lethal oxidants produced by phagocytes. Subsequent multiplication of the microbes within phagosomes may eventually destroy the phagocyte.
Abscesses and Ulcers
If pus cannot drain out of an inflamed region, the result is an abscess—an excessive accumulation of pus in a confined
space. Common examples are pimples and boils.
When superficial inflamed tissue sloughs off the surface of an organ or tissue, the resulting open sore is called an ulcer.
People with poor circulation— for instance, diabetics with advanced atherosclerosis—are susceptible to ulcers in the tissues of their legs. These ulcers, which are called stasis ulcers, develop because of poor oxygen and nutrient supply to tissues that then become very susceptible to a very mild injury or infection.
Cytokine therapy is the use of cytokines to treat medical conditions. Interferons were the first cytokines shown to have limited effects against some human cancers.
Alpha-interferon is approved in the United States for treating Kaposi sarcoma, a cancer that often occurs in patients infected with HIV, the virus that causes AIDS.
Other approved uses for alpha interferon include
- treating genital herpes caused by the herpes virus;
- treating hepatitis B and C, caused by the hepatitis B and C viruses;
- and treating hairy cell leukemia.
A form of beta-interferon slows the progression of multiple sclerosis (MS) and lessens the frequency and severity of MS attacks.
Of the interleukins, the one most widely used to fight cancer is interleukin-2. Although this treatment is effective in causing tumor regression in some patients, it also can be very toxic. Among the adverse effects are high fever, severe weakness, difficulty breathing due to pulmonary edema, and hypotension leading to shock.
Graft Rejection and Tissue Typing
Organ transplantation involves the replacement of an injured or diseased organ, such as the heart, liver, kidney, lungs, or pancreas, with an organ donated by another individual.
Usually, the immune system recognizes the proteins in the transplanted organ as foreign and mounts both cell-mediated and antibody-mediated immune responses against them. This phenomenon is known as graft rejection.
The success of an organ or tissue transplant depends on histocompatibility —that is, the tissue compatibility between the donor and the recipient. The more similar the MHC antigens, the greater the histocompatibility, and thus the greater the probability that the transplant will not be rejected. Tissue typing (histocompatibility testing) is done before any organ transplant.
The closer the match between the major histocompatibility complex proteins of the donor and recipient, the weaker is the graft rejection response. To reduce the risk of graft rejection, organ transplant recipients receive immunosuppressive drugs. Thus, the risk of rejection is diminished while resistance to some diseases is maintained.
Although the immune system responds to cancerous cells, often immunity provides inadequate protection, as evidenced by the number of people dying each year from cancer. Considerable research is focused on cancer immunology, the study of ways to use immune responses for detecting, monitoring, and treating cancer.
For example, some tumors of the colon release carcinoembryonic antigen (CEA) into the blood, and prostate cancer cells release prostate-specific antigen (PSA).
Detecting these antigens in blood does not provide definitive diagnosis of cancer, because both antigens are also released in certain noncancerous conditions. However, high levels of cancer-related antigens in the blood often do indicate the presence of a malignant tumor.
Finding ways to induce our immune system to mount vigorous attacks against cancerous cells has been an elusive goal. Many different techniques have been tried, with only modest success.
In one method, inactive lymphocytes are removed in a blood sample and cultured with interleukin-2. The resulting lymphokine-activated killer (LAK) cells are then transfused back into the patient’s blood. Although LAK cells have produced dramatic improvement in a few cases, severe complications affect most patients.
In another method, lymphocytes procured from a small biopsy sample of a tumor are cultured with interleukin-2. After their proliferation in culture, such tumor-infiltrating lymphocytes (TILs) are reinjected. About a quarter of patients with malignant melanoma and renal-cell carcinoma who received TIL therapy showed significant improvement.
The many studies currently under way provide reason to hope that immune-based methods will eventually lead to cures for cancer.
THE RESPIRATORY SYSTEM
Pneumothorax and Hemothorax
Separate pleural cavities surround the left and right lungs. Inflammation of the pleural membrane, called pleurisy or pleuritis, may in its early stages cause pain due to friction between the parietal and visceral layers of the pleura. If the inflammation persists, excess fluid accumulates in the pleural space, a condition known as pleural effusion.
In certain conditions, the pleural cavities may fill with air (pneumothorax, blood (hemothorax), or pus.
Air in the pleural cavities, most commonly introduced in a surgical opening of the chest or as a result of a stab or gunshot wound, may cause the lungs to collapse. This collapse of a part of a lung, or rarely an entire lung, is called atelectasis (at-e-LEK-ta-sis; ateles- incomplete; -ectasis expansion).
The goal of treatment is the evacuation of air (or blood) from the pleural space, which allows the lung to reinflate. A small pneumothorax may resolve on its own, but it is often necessary to insert a chest tube to assist in evacuation.
Carbon Monoxide Poisoning
Carbon monoxide (CO) is a colorless and odorless gas found in
- exhaust fumes from automobiles,
- gas furnaces and space heaters,
- and in tobacco smoke.
It is a by-product of the combustion of carbon- containing materials such as coal, gas, and wood. CO binds to the heme group of hemoglobin, just as O2 does, except that the binding of carbon monoxide to hemoglobin is over 200 times as strong as the binding of O2 to hemoglobin.
Elevated blood levels of CO cause carbon monoxide poisoning, which can cause the lips and oral mucosa to appear bright, cherry-red (the color of hemoglobin with carbon monoxide bound to it).
Without prompt treatment, carbon monoxide poisoning is fatal. It is possible to rescue a victim of CO poisoning by administering pure oxygen, which speeds up the separation of carbon monoxide from hemoglobin.
Hypoxia is a deficiency of O2 at the tissue level.
Based on the cause, we can classify hypoxia into four types, as follows:
- Hypoxic hypoxia is caused by a low PO2 in arterial blood as a result of high altitude, airway obstruction, or fluid in the lungs.
- In anemic hypoxia, too little functioning hemoglobin is present in the blood, which reduces O2 transport to tissue cells. Among the causes are hemorrhage, anemia, and failure of hemoglobin to carry its normal complement of O2, as in carbon monoxide poisoning.
- In ischemic hypoxia, blood flow to a tissue is so reduced that too little O2 is delivered to it, even though PO2 and oxyhemoglobin levels are normal.
- In histotoxic hypoxia, the blood delivers adequate O2 to tissues, but the tissues are unable to use it properly
because of the action of some toxic agent. One cause is cyanide poisoning, in which cyanide blocks an enzyme required for the use of O2 during ATP synthesis.
Effects of Smoking on the Respiratory System
Smoking may cause a person to become easily “winded” during even moderate exercise because several factors decrease respiratory efficiency in smokers:
- Nicotine constricts terminal bronchioles, which decreases airflow into and out of the lungs.
- Carbon monoxide in smoke binds to hemoglobin and reduces its oxygen-carrying capability.
- Irritants in smoke cause increased mucus secretion by the mucosa of the bronchial tree and swelling of the mucosal lining, both of which impede airflow into and out of the lungs.
- Irritants in smoke also inhibit the movement of cilia and destroy cilia in the lining of the respiratory system. Thus, excess mucus and foreign debris are not easily removed, which further adds to the difficulty in breathing.
- With time, smoking leads to destruction of elastic fibers in the lungs and is the prime cause of emphysema. These changes cause collapse of small bronchioles and trapping of air in alveoli at the end of exhalation. The result is less efficient gas exchange.
THE DIGESTIVE SYSTEM
A common cause of peritonitis, an acute inflammation of the peritoneum, is contamination of the peritoneum by infectious microbes, which can result from accidental or surgical wounds in the abdominal wall, or from perforation or rupture of abdominal organs.
If, for example, bacteria gain access to the peritoneal cavity through an intestinal perforation or rupture of the appendix, they can produce an acute, life-threatening form of peritonitis.
A less serious (but still painful) form of peritonitis can result from the rubbing together of inflamed peritoneal surfaces.
The increased risk of peritonitis is of particular concern to those who rely on peritoneal dialysis, a procedure in which the peritoneum is used to filter the blood when the kidneys do not function properly.
Although any of the salivary glands may be the target of a nasopharyngeal infection, the mumps virus typically
attacks the parotid glands. Mumps is an inflammation and enlargement of the parotid glands accompanied by
- moderate fever,
- malaise (general discomfort),
- and extreme pain in the throat, especially when swallowing sour foods or acidic juices.
- Swelling occurs on one or both sides of the face, just anterior to the ramus of the mandible.
In about 30% of males past puberty, the testes may also become inflamed; sterility rarely occurs because testicular involvement is usually unilateral (one testis only). Since a vaccine became available for mumps in 1967, the incidence of the disease has declined dramatically.
Gastroesophageal Reflux Disease
If the lower esophageal sphincter fails to close adequately after food has entered the stomach, the stomach contents can
reflux (back up) into the inferior portion of the esophagus. This condition is known as gastroesophageal reflux disease (GERD).
Hydrochloric acid (HCl) from the stomach contents can irritate the esophageal wall, resulting in a burning sensation that is called heartburn because it is experienced in a region very near the heart; it is unrelated to any cardiac problem.
Drinking alcohol and smoking can cause the sphincter to relax, worsening the problem. The symptoms of GERD often can be controlled by avoiding foods that strongly stimulate stomach acid secretion (coffee, chocolate, tomatoes, fatty foods, orange juice, peppermint, spearmint, and onions). Other acid-reducing strategies include taking over-the-counter histamine-2 (H2) blockers 30 to 60 minutes before eating to block acid secretion, and neutralizing acid that has already been secreted with antacids.
Symptoms are less likely to occur if food is eaten in smaller amounts and if the person does not lie down immediately after a meal. GERD may be associated with cancer of the esophagus.
Pylorospasm and Pyloric Stenosis
Two abnormalities of the pyloric sphincter can occur in infants.
In pylorospasm, the smooth muscle fibers of the sphincter fail to relax normally, so food does not pass easily from the stomach to the small intestine, the stomach becomes overly full, and the infant vomits often to relieve the pressure. Pylorospasm is treated by drugs that relax the muscle fibers of the pyloric sphincter.
Pyloric stenosis is a narrowing of the pyloric sphincter that must be corrected surgically. The hallmark symptom is projectile vomiting—the spraying of liquid vomitus some distance from the infant.
Vomiting or emesis is the forcible expulsion of the contents of the upper GI tract (stomach and sometimes duodenum) through the mouth.
The strongest stimuli for vomiting are irritation and distension of the stomach;
Other stimuli include
- unpleasant sights,
- general anesthesia,
- and certain drugs such as morphine and derivatives of digitalis.
Nerve impulses are transmitted to the vomiting center in the medulla oblongata, and returning impulses propagate to the
- upper GI tract organs,
- and abdominal muscles.
Vomiting involves squeezing the stomach between the diaphragm and abdominal muscles and expelling the contents through open esophageal sphincters. Prolonged vomiting, especially in infants and elderly people, can be serious because the loss of acidic gastric juice can lead to alkalosis (higher than normal blood pH), dehydration, and damage to the esophagus and teeth.
Pancreatitis and Pancreatic Cancer
Inflammation of the pancreas, as may occur in association with alcohol abuse or chronic gallstones, is called pancreatitis.
In a more severe condition known as acute pancreatitis, which is associated with heavy alcohol intake or biliary tract obstruction, the pancreatic cells may release either trypsin instead of trypsinogen or insufficient amounts of trypsin inhibitor, and the trypsin begins to digest the pancreatic cells.
Patients with acute pancreatitis usually respond to treatment, but recurrent attacks are the rule. In some people pancreatitis is idiopathic, meaning that the cause is unknown.
Other causes of pancreatitis include
- cystic fibrosis,
- high levels of calcium in the blood (hypercalcemia),
- high levels of blood fats (hyperlipidemia or hypertriglyceridemia),
- some drugs,
- and certain autoimmune conditions.
However, in roughly 70% of adults with pancreatitis, the cause is alcoholism. Often the first episode happens between ages 30 and 40.
Pancreatic cancer usually affects people over 50 years of age and occurs more frequently in males. Typically, there are few symptoms until the disorder reaches an advanced stage and often not until it has metastasized to other parts of the body such as the lymph nodes, liver, or lungs. The disease is nearly always fatal and is the fourth most common cause of death from cancer in the United States.
Pancreatic cancer has been linked to
- fatty foods,
- high alcohol consumption,
- genetic factors,
- and chronic pancreatitis.
Jaundice is a yellowish coloration of the
- sclerae (whites of the eyes),
- and mucous membranes
due to a buildup of a yellow compound called bilirubin.
After bilirubin is formed from the breakdown of the heme pigment in aged red blood cells, it is transported to the liver, where it is processed and eventually excreted into bile.
The three main categories of jaundice are
- Prehepatic jaundice, due to excess production of bilirubin;
- Hepatic jaundice, due to congenital liver disease, cirrhosis of the liver, or hepatitis;
- Extrahepatic jaundice, due to blockage of bile drainage by gallstones or cancer of the bowel or the pancreas.
Because the liver of a newborn functions poorly for the first week or so, many babies experience a mild form of jaundice called neonatal (physiological) jaundice that disappears as the liver matures. Usually, it is treated by exposing the infant to blue light, which converts bilirubin into substances the kidneys can excrete.
Liver Function Tests
Liver function tests are blood tests designed to determine the presence of certain chemicals released by liver cells. These include
- albumin globulinase,
- alanine aminotransferase (ALT),
- aspartate aminotransferase (AST),
- alkaline phosphatase (ALP),
- gamma-glutamyl-transpeptidase (GGT),
- and bilirubin.
The tests are used to evaluate and monitor liver disease or damage.
Common causes of elevated liver enzymes include
- nonsteroidal anti-inflammatory drugs,
- cholesterol-lowering medications,
- some antibiotics,
- infections (viral hepatitis and mononucleosis),
- tumors of the liver,
- and excessive use of herbal supplements such as kava, comfrey, pennyroyal, dandelion root, skullcap, and ephedra.
If bile contains either insufficient bile salts or lecithin or excessive cholesterol, the cholesterol may crystallize to form gallstones.
As they grow in size and number, gallstones may cause
- or complete obstruction
to the flow of bile from the gallbladder into the duodenum.
Treatment consists of using gallstone-dissolving drugs, shock-wave therapy, or surgery.
For people with a history of gallstones or for whom drugs or lithotripsy are not options, cholecystectomy, the removal of the gallbladder and its contents is necessary.
To prevent side effects resulting from a loss of the gallbladder, patients should make lifestyle and dietary changes, including the following:
- (1) limiting the intake of saturated fat;
- (2) avoiding the consumption of alcoholic beverages;
- (3) eating smaller amounts of food during a meal and eating five to six smaller meals per day instead of two to three larger meals;
- (4) taking vitamin and mineral supplements.
In some people the absorptive cells of the small intestine fail to produce enough lactase, which is essential for the digestion of lactose.
This results in a condition called lactose intolerance, in which undigested lactose in chyme causes fluid to be retained in the feces; bacterial fermentation of the undigested lactose results in the production of gases.
Symptoms of lactose intolerance include diarrhea, gas, bloating, and abdominal cramps after consumption of milk and other dairy products. The symptoms can be relatively minor or serious enough to require medical attention.
The hydrogen breath test is often used to aid in diagnosis of lactose intolerance. Very little hydrogen can be detected in the breath of a normal person, but hydrogen is among the gases produced when undigested lactose in the colon is fermented by bacteria. The hydrogen is absorbed from the intestines and carried through the bloodstream to the lungs, where it is exhaled.
Persons with lactose intolerance should select a diet that restricts lactose (but not calcium) and take dietary supplements to aid in the digestion of lactose.
Inflammation of the appendix, termed appendicitis, is preceded by obstruction of the lumen of the appendix by
- a foreign body,
- a carcinoma of the cecum,
- or kinking of the organ.
It is characterized by high fever, elevated white blood cell count, and a neutrophil count higher than 75%. The infection that follows may result in edema and ischemia and may progress to gangrene and perforation within 24 hours.
Typically, appendicitis begins with
- referred pain in the umbilical region of the abdomen,
- followed by anorexia (loss of appetite for food),
- nausea, and vomiting.
After several hours the pain localizes in the right lower quadrant (RLQ) and is continuous, dull or severe, and intensified by coughing, sneezing, or body movements.
Early appendectomy (removal of the appendix) is recommended because it is safer to operate than to risk rupture, peritonitis, and gangrene. Although it required major abdominal surgery in the past, today appendectomies are usually performed laparoscopically.
Polyps in the Colon
Polyps in the colon are generally slow-developing benign growths that arise from the mucosa of the large intestine.
Often, they do not cause symptoms. If symptoms do occur, they include diarrhea, blood in the feces, and mucus discharged from the anus. The polyps are removed by colonoscopy or surgery because some of them may become cancerous.
Dietary fiber consists of indigestible plant carbohydrates— such as
- and pectin
Found in fruits, vegetables, grains, and beans.
Insoluble fiber, which does not dissolve in water, includes the woody or structural parts of plants such as the skins of fruits and vegetables and the bran coating around wheat and corn kernels. Insoluble fiber passes through the GI tract largely unchanged but speeds up the passage of material through the tract.
Soluble fiber, which does dissolve in water, forms a gel that slows the passage of material through the tract. It is found in abundance in
- and citrus fruits.
People who choose a fiber-rich diet may reduce their risk of developing
- and colorectal cancer.
Soluble fiber also may help lower blood cholesterol.
The liver normally converts cholesterol to bile salts, which are released into the small intestine to help fat digestion. Having accomplished their task, the bile salts are reabsorbed by the small intestine and recycled back to the liver. Since soluble fiber binds to bile salts to prevent their reabsorption, the liver makes more bile salts to replace those lost in feces. Thus, the liver uses more cholesterol to make more bile salts and blood cholesterol level is lowered.
METABOLISM AND NUTRITION
The level of ketone bodies in the blood normally is very low because other tissues use them for ATP production as fast as they are generated from the breakdown of fatty acids in the liver. During periods of excessive beta oxidation, however, the production of ketone bodies exceeds their uptake and use by body cells.
This might occur after a meal rich in triglycerides, or during fasting or starvation, because few carbohydrates are available for catabolism.
Excessive beta oxidation may also occur in poorly controlled or untreated diabetes mellitus for two reasons:
- (1) Because adequate glucose cannot get into cells, triglycerides are used for ATP production,
- (2) because insulin normally inhibits lipolysis, a lack of insulin accelerates the pace of lipolysis.
When the concentration of ketone bodies in the blood rises above normal—a condition called ketosis—the ketone bodies, most of which are acids, must be buffered. If too many accumulate, they decrease the concentration of buffers, such as bicarbonate ions, and blood pH falls.
Extreme or prolonged ketosis can lead to acidosis (ketoacidosis), an abnormally low blood pH. The decreased blood pH in turn causes depression of the central nervous system, which can result in disorientation, coma, and even death if the condition is not treated. When a diabetic becomes seriously insulin-deficient, one of the telltale signs is the sweet smell on the breath from the ketone body acetone.
Hypothermia is a lowering of core body temperature to 35C (95F) or below. Causes of hypothermia include
- an overwhelming cold stress (immersion in icy water),
- metabolic diseases (hypoglycemia, adrenal insufficiency, or hypothyroidism),
- drugs (alcohol, antidepressants, sedatives, or tranquilizers),
- and malnutrition.
Hypothermia is characterized by the following as core body temperature falls:
- sensation of cold,
- muscle rigidity,
- loss of spontaneous movement,
- and death (usually caused by cardiac arrhythmias).
Because the elderly have reduced metabolic protection against a cold environment coupled with a reduced perception of cold, they are at greater risk for developing hypothermia.
THE URINARY SYSTEM
Loss of Plasma Proteins in Urine Causes Edema
In some kidney diseases, glomerular capillaries are damaged and become so permeable that plasma proteins enter glomerular filtrate.
As a result, the filtrate exerts a colloid osmotic pressure that draws water out of the blood.
- In this situation, the NFP increases, which means more fluid is filtered.
- At the same time, blood colloid osmotic pressure decreases because plasma proteins are being lost in the urine.
- Because more fluid filters out of blood capillaries into tissues throughout the body than returns via reabsorption, blood volume decreases and interstitial fluid volume increases.
- Thus, loss of plasma proteins in urine causes edema, an abnormally high volume of interstitial fluid.
When the blood concentration of glucose is above 200 mg/mL, the renal symporters cannot work fast enough to reabsorb all the glucose that enters the glomerular filtrate. As a result, some glucose remains in the urine, a condition called glucosuria.
The most common cause of glucosuria is diabetes mellitus, in which the blood glucose level may rise far above normal because insulin activity is deficient. Excessive glucose in the glomerular filtrate inhibits water reabsorption by kidney tubules. This leads to increased urinary output (polyuria), decreased blood volume, and dehydration.
Diuretics are substances that slow renal reabsorption of water and thereby cause diuresis, an elevated urine flow rate, which in turn reduces blood volume. Diuretic drugs often are prescribed to treat hypertension (high blood pressure) because lowering blood volume usually reduces blood pressure.
Naturally occurring diuretics include
- caffeine in coffee, tea, and sodas, which inhibits Na reabsorption,
- and alcohol in beer, wine, and mixed drinks, which inhibits secretion of ADH.
Most diuretic drugs act by interfering with a mechanism for reabsorption of filtered Na.
Indicators of Na Imbalance
If excess sodium ions remain in the body because the kidneys fail to excrete enough of them, water is also osmotically retained.
The result is
- increased blood volume,
- increased blood pressure,
- and edema,
- an abnormal accumulation of interstitial fluid.
Renal failure and hyperaldosteronism (excessive aldosterone secretion) are two causes of Na retention.
Excessive urinary loss of Na, by contrast, causes excessive water loss, which results in hypovolemia, an abnormally low blood volume.
Hypovolemia related to Na loss is most frequently due to the inadequate secretion of aldosterone associated with adrenal insufficiency or overly vigorous therapy with diuretic drugs.