Age changes in appearance and physical functioning in adulthood are inevitable, but they occur at different rates in different individuals and species. The effects of these changes on the self-concept also vary from person to person. Greying hair, wrinkles, and other signs of old age are obviously of greater concern to individuals for whom a youthful appearance is more important for occupational success and social prestige. Physical appearance, of course, is not the exclusive concern of aging women, though the cosmetics industry and purveyors of other "treatments" for aging skin and bodies focus principally on the female sex.
Aging is accompanied by alterations in physical appearance and by declines in the structure and functioning of the cardivascular, respiratory, musculoskeletal, gastrointestinal, genitourinary, and nervous systems, as well as the sense organs. The efficiency with which the heart pumps blood is affected by the thickening and stiffening of heart muscle and valves and the narrowing of coronary arteries. The result is a decline in the rate at which oxygen and nutrients are conveyed to the body cells and waste products are carried away.
The respiratory system interacts with the heart in supplying clean, oxygenated blood to the body. Shortness of breath and other respiratory problems associated with aging are caused by structural changes in the lungs and the supporting muscles. Functioning of both the heart and lungs is affected not only by primary aging but also by secondary factors in the environment and the person's lifestyle.
A decrease in muscle tissue, cartilage, and synovial fluid, and an increase in fat tissue and bone mineral salts during middle adulthood affect the tone, strength, flexibility, speed, and stamina of the muscles. The bones and joints are also affected, increasing the stiffness and painfulness of movement. Consequently, the movements of older adults are characteristically slower than those of younger adults.
Declines in the efficiency of digestion and elimination during later life are caused by changes in the stomach, intestines, liver, gall bladder, and teeth. Shrinkage of the kidneys, decreased bladder elasticity and capacity, and enlargement of the prostate gland combine to produce urinary malfunctions. Changes in the sex glands and organs also contribute to a decline in sexual activity during middle- and late life.
Age-related changes in the nervous system include decreases in the number and size of neurons and increases in plaque and neurofibrillary tangles in the brain. The effects are slower and weaker responses and declines in certain cognitive functions. The ability of the body to ward off infection and disease is affected by decreased functioning of the immune system.
With respect to sensation and perception, presbyopia ("old-sighted-ness"), cataracts, and presbycusis (inner-ear deafness) are common accom-paniers of aging. More severe but also less common disorders of vision, such as glaucoma, macular degeneration, and retinal detachment, also increase with aging. The senses of touch, vibration, temperature, pain, kinesthetic, and balance decline with aging. Although inevitable, age-related changes in the internal organs and sense receptors vary greatly from person to person. Heredity is certainly a factor in determining structural and functional changes with aging, but injury, disease, nutrition, exercise, smoking, environmental pollution, and other lifestyle factors exert considerable influences on the rate and severity of these changes.
Theories of aging include (1) wear-and-tear explanations that the body's tissues, organs, or cells gradually wear out as a result of overuse or accidents; (2) substance explanations that aging is caused by the accumulation of errors or chemical garbage such as free radicals and lipofuscins; (c) hormonal theories that implicate the activities of the hypothalamus, pituitary, and thyroid glands; (d) genetic theories of a programmed limit (an "aging clock") to the life span. No single theory is adequate in itself to explain the aging process. Rather it appears that a combination of theories or hypotheses, confirmed by research, will be needed to explain why we age.
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