Aging

Aging, irreversible biological changes that occur in all living things with the passage of time, eventually resulting in death. Although all organisms age, rates of aging vary considerably. Fruit flies, for example, are born, grow old, and die in 30 or 40 days, while field mice have a life span of about three years. Dolphins may live to age 25, elephants to age 50, and Galápagos tortoises to 100. These life spans pale in comparison to those of some species of giant sequoia trees, which live hundreds of years.

Among humans, the effects of aging vary from one individual to another. The average life expectancy is around 75 years, almost twice what it was in the early 1900s. Although some people never reach this age, and others are beset with illnesses if they do, more and more people are living healthy lives well into their 90s and older. The study of the different aging processes that occur among individuals and the factors that cause these changes is known as gerontology. Geriatrics is a medical specialty concerned with the prevention, diagnosis, and treatment of diseases in the elderly.

Several general changes take place in the human body as it ages: hearing and vision decline, muscle strength lessens, soft tissues such as skin and blood vessels become less flexible, and there is an overall decline in body tone.

Most of the body's organs perform less efficiently with advancing age. For example, the average amount of blood pumped by the heart drops from about 6.9 liters (7.3 quarts) per minute at age 20 to only 3.5 liters (3.7 quarts) pumped per minute at age 85. For this same age range, the average amount of blood flowing through the kidneys drops from approximately 0.6 liters (0.6 quarts) per minute to 0.3 liters (0.3 quarts). Not all people experience decreased organ function to the same degree—some individuals have healthier hearts and kidneys at age 85 than others do at age 50.

The immune system also changes with age. A healthy immune system protects the body against bacteria, viruses, and other harmful agents by producing disease-fighting proteins known as antibodies. A healthy immune system also prevents the growth of abnormal cells, which can become cancerous. With advancing age, the ability of the immune system to carry out these protective functions is diminished—the rate of antibody production may drop by as much as 80 percent between age 20 and age 85. This less-effective immune system explains why a bout of influenza, which may make a young adult sick for a few days, can be fatal for an elderly person. Thus, it is as important for an older person to be vaccinated against the flu and pneumonia as it is for young people to be vaccinated against childhood diseases.

Abscess

Abscess, collection of pus, a thick, yellowish fluid caused by bacterial, protozoan, or fungal invasion of body tissues. Abscesses can occur in the skin, in the gums, in bone, and in body organs, such as the liver, the lungs, and even the brain. The area of the abscess becomes red and swollen; sensations of pain and localized heat are common. If the inflamed tissue encompassing the infected cavity thins out sufficiently, the abscess may rupture. Treatment may involve surgical incision or use of antibiotics or both.

Thrombosis

Thrombosis, formation of a blood clot, or thrombus, inside a blood vessel. Forming a clump of various blood cells, the clot remains attached at its point of formation, partially or completely blocking the flow of blood through the vessel. A clot that breaks free and travels to a different part of the circulatory system is called an embolism.

The chief causes of thrombosis are injury to the inner lining of a blood vessel; blood disorders that result in thickened blood and an increased tendency toward clotting; and restricted blood flow, caused by such problems as obesity. People with the condition known as atherosclerosis are at special risk for thrombosis because their arteries are partially blocked by an accumulation of fatty tissue largely due to elevated levels of cholesterol in the blood. Diets high in saturated fats, such as in eggs and dairy products, are likely to raise blood cholesterol levels.

When thrombosis occurs in an artery, the tissues that the artery normally supplies with blood suffer infarction—that is, they die from a lack of blood-borne nutrients. Coronary thrombosis, the blockage of an artery that supplies blood to heart muscle, results in a myocardial infarction, or heart attack. Cerebral thrombosis, thrombosis in an artery leading to the brain, results in a stroke. Blood clots may cause obstructions in arteries leading to the retina of the eye, the kidneys, the intestines, as well as to the limbs.

Veins as well as arteries may be damaged by thrombosis. When a clot forms in a vein near the surface of the skin, it leads to thrombophlebitis. This condition causes swelling and inflammation where the clot develops in the vein. People with varicose veins are at particular risk for this disorder. Deep vein thrombosis usually strikes older people with poor blood circulation that results from a weakened heart or an extended period of bed rest. Obesity may also contribute to deep vein thrombosis.

The treatment of thrombosis usually involves the administration of anticoagulants, or drugs that discourage clotting. Anticoagulants range from simple medications like aspirin to complex organic acids like heparin. Enzymes such as streptokinase that are capable of dissolving clots may be administered as an alternative. There are also surgical techniques for removing particularly threatening clots.

Arteriosclerosis

Arteriosclerosis, a group of disorders of the arteries, the tubular vessels that carry oxygen-carrying blood from the heart to the body’s organs and tissues. In arteriosclerosis, the walls of the arteries thicken, harden, and lose their elasticity. The blood vessel channels develop twists and turns and become narrowed so that the heart must work harder than normal to pump blood through the arteries. In the disease’s advanced stage, there is a risk of a decrease in blood flow and oxygen supply to all parts of the body. The disorder, commonly known as hardening of the arteries, develops as people age, but its severity varies greatly from person to person. Little is known about the cause of arteriosclerosis. Heredity appears to play a role in many cases. Lifestyle factors, such as continual stress or a diet abundant in animal fats, also appear to contribute to the condition.

The most common form of arteriosclerosis is atherosclerosis, also known as coronary artery disease. In this condition, deposits of plaque—a material rich in greasy compounds called lipids, including cholesterol—form on the inner walls of the arteries. These deposits narrow the arterial channels and partly block the normal flow of blood through them. Calcium is often deposited with the fatty material and scar tissue develops, stiffening the walls of the arteries. As the blood passes over the roughened artery walls, blood clots begin to form upon them, a condition called thrombosis. These blood clots can partially or totally block the artery. Although it may occur in any artery in any part of the body, atherosclerosis causes most of its damage by reducing the flow of blood to the heart, brain, kidneys, and legs.

The symptoms of arteriosclerosis depend upon the arteries affected. A decrease in the flow of blood through the coronary arteries, resulting in a shortage of oxygen going to the heart muscle, causes chest pains, a condition called angina pectoris. If a blood clot forms in a coronary artery, the interruption of the blood flow can result in the death of part of the heart muscle, causing the crushing chest pains of a heart attack. A chronic decrease in the circulation of blood to the heart may result in heart failure, which is the inability of the heart muscle to pump enough blood for the body’s requirements. Unless treated, this condition is fatal.

When arteriosclerosis occurs in the arteries to the brain, the decrease in blood flow and oxygen can cause mental confusion and personality changes. A stroke may occur if an artery in the brain that has been weakened by arteriosclerosis ruptures or a blood clot halts blood flow to the brain, possibly resulting in partial paralysis, loss of speech, and sometimes death.

There is no specific treatment for arteriosclerosis. Often a low-fat diet is prescribed. Doctors usually advise patients to stop smoking and to exercise regularly. Drug treatment can include the use of calcium channel blockers to expand the arteries so that blood can flow more freely, and anticoagulants to prevent blood clots from forming in diseased arteries. In advanced cases, surgery to replace diseased blood vessels with grafts of healthy arteries may be necessary.

Aneurysm

Aneurysm is a bulge or sac formed by the ballooning of the wall of an artery or a vein. An aneurysm may pose a threat to health. It may become the site of a blood clot that breaks away and lodges in the tissues of such vital organs as the heart and the brain, causing serious, even mortal, heart failure or brain damage. A ruptured aneurysm may lead to a fatal loss of blood from the circulatory system into body cavities.

Most aneurysms occur in blood vessel walls that have been weakened by a combination of arteriosclerosis, thickening and hardening of the arteries, and hypertension, abnormally high blood pressure. However, even normal blood pressure may cause an aneurysm in a vessel wall that has been weak from birth. Other causes of aneurysms include traumatic injury, such as that experienced in an automobile accident, and infection from diseases, such as syphilis. Aneurysms may develop in any blood vessel, but they frequently form in the major vessels, especially in the aorta, which is the body’s largest artery.

Aneurysms often produce no outward symptoms, and may be discovered only during a physical examination, from an X ray, or when they rupture. If the aneurysm is near the surface of the body, the patient may become aware of a pulsating mass. Some aneurysms may press on adjacent organs. In the chest, for example, the pressure of an aneurysm may affect the respiratory system, causing hoarseness, coughing, breathlessness, and pain. Abdominal aortic aneurysms are known to cause severe pain in the back and lower abdomen. Brain aneurysms are generally accompanied by no symptoms at all until they suddenly enlarge and burst, possibly resulting in death.

Some aneurysms can be removed surgically before they pose a danger. The risk of death is much lower in these cases than if the patient requires emergency surgery because of a ruptured aneurysm.