Aging is accompanied by expected, gradual, and progressive changes in organs and systems. Peak function occurs in most organs in the second and third decade of life followed by gradual decline. Most manifestations are subtle and seldom affect daily function. As a result of age-related changes, there is a decline in homeostatic reserves. During periods of increased demand or stress induced by illness, the older adult may experience the reserves to be inadequate for the situation. In particular, physiological changes are expected over time and need to be distinguished from pathological changes resulting from disease. Chronological and biological aging do not necessarily match; aging is highly variable and individualized. Successful aging is the result of several factors including genetics, prevention and management of illness, lifestyle, and environmental factors.
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