Effects of Aging and Death

Although humans are aging from the time they are born, aging is generally used to describe adults past their physical peak. In biological terms, aging adults undergo senescence, which is the degeneration of organ systems that takes place between the age of peak physical form and death. Senescence involves a decreased ability to repair damage to cells and tissues, heal from disease, and recover from physical stress, as well as an increased susceptibility to disease.

Senescence occurs at different rates across all body systems. Aging adults lose bone mass or bone density in a condition called osteopenia, or the more severe osteoporosis. Females lose more bone mass than males. In females estrogen production is directly related to protecting bones, and after menopause, the reduction in estrogen production results in bone loss. These skeletal changes increase the risk of fractures and decrease the ability to heal from them. Osteoarthritis, which is degeneration of cartilage and bone in joints, and degenerative joint diseases become more common. In the integumentary system, hair grays and thins, sebaceous glands atrophy, skin loses elasticity and sensory function, and blood vessels become fragile. Senescence of the muscular system leads to weakness and muscular atrophy. In the nervous system, adults lose brain tissue and synapses. Although the aging adult nervous system continues to produce new synapses, the process is slower than in a child's brain, and loss in aging adults exceeds production, thus reducing the number of synapses. Motor coordination, short-term memory, and intellectual function diminish. Several sensory organs also lose function; hearing, vision, and the ability to taste and smell all begin to decline. Glaucoma and cataracts are degenerative eye conditions that reduce vision. Glaucoma increases pressure within the eye, which results in loss of vision. Cataracts are a clouding of the eye lens, which is caused by the breakdown of natural proteins in the eye. This normally begins to occur at 40 years of age, but by age 60, clouding is more severe and may require corrective surgery to remove. The endocrine system undergoes limited senescence, except for the drop in reproductive hormones. Males secrete less testosterone and experience reduced sperm count and libido. Females undergo menopause, the ceasing of menstruation. The loss of estrogen reduces libido, increases vaginal dryness, and raises susceptibility to atherosclerosis—hardening of the arteries caused by fat deposits—and osteoporosis. Senescence of the circulatory system causes significant health problems and a high percentage of deaths. Atherosclerosis becomes more common, as do thrombosis (formation of blood clots), varicose veins, anemia, edema, and hemorrhoids. In the immune system, senescence reduces resistance to infectious diseases in the elderly and increases their cancer risk.

Senescence of the respiratory system occurs because of the thoracic cage's decreased flexibility and a decline in lung alveoli. This change causes reduced pulmonary function, which decreases oxygen levels to the brain and muscles. Because organ function is directly related to oxygen flow through the blood, reduction of oxygen levels shows negative effects on brain and muscle function. The urinary system exhibits marked senescence, as kidneys atrophy significantly over time. Older adults are thus susceptible to water imbalances and problems clearing toxins and medications. Many elderly males experience an enlarged prostate and increased urine retention. The enlarged prostate reduces urine flow through the ureter, which results in an inability to efficiently empty urine from the bladder. Aging females are prone to increased urinary incontinence. In the aging digestive system, the stomach atrophies and liver function declines. Older adults experience decreased salivation and have poorer dental health. They have more difficulty in swallowing and have increased issues with gastroesophageal reflux, constipation, and loss of appetite.

In biological terms, death is when a body completely ceases respiratory or circulatory functions or when the brain ceases electrical activity. Whether an individual's dying process takes place rapidly or over a long period of time, death results from failures of multiple body systems. Failure of one organ can trigger cascading effects in other organs. For instance, a prolonged disease affecting the kidneys can lead to a dangerous buildup of wastes in the blood. High toxicity levels can, in turn, diminish brain function and respiration and eventually cause cardiac arrest when the heart stops beating. A rapid death such as that from a myocardial infarction (heart attack) affects multiple systems quickly. Cardiac arrest shuts down cardiopulmonary functions, depriving all other body systems of needed blood and oxygen. In turn, a brain deprived of oxygen halts processes critical to sustaining life.

For many elderly people, organ senescence, vulnerability to infection, and inability to fight disease eventually bring on life-threatening conditions that lead to death. Older adults may experience long periods in which they deal with health complications before they encounter one—or a combination of many—that proves fatal.

The actual instance of biological death is hard to define, particularly as some organs continue to function for a brief period after heart activity ends. Legally, death was previously considered to occur at the moment the heart stopped beating and respiration ceased. Now, however, cardiopulmonary function can be maintained by artificial means in a hospital. The medical community currently uses brain death as the necessary condition to declare an individual legally dead. Brain death is defined as the permanent loss of brain activity—a condition that shuts down respiration and all other vital functions. Doctors use specific criteria to diagnose and confirm brain death.

In the United States, the leading cause of death is heart disease, followed closely by cancer. Unintentional injuries, respiratory diseases, and strokes make up the next most common causes of U.S. deaths. However, these occur at much lower rates than heart disease and cancer. The remainder of the top ten causes of U.S. deaths are, in descending order, Alzheimer's disease, type 2 diabetes, influenza and pneumonia, kidney disease, and suicide.