ABSTRACT
Aging is a generalized physiologic process that progressively decreases the ability of an organism to adapt to environmental change and increases its vulnerability to disease and death. Aging results in a diminution of reserves of most physiologic systems. It affects cells and the systems made up of them, as well as tissue components. Aging is a characteristic of all higher organisms. The diversity of age-related impairments has led many gerontologists to conclude that no general mechanism is likely to underlie these changes. Therefore, numerous theories have been advanced to explain the phenomenon of aging.
