A second theory of aging suggests that a hormonal decline can affect many different organ systems. The immune system no longer performs as well, which is perhaps why cancer is more prevalent in the elderly. Aging may be due to the failure of a particular tissue type found throughout the body. A third theory on aging suggests that years of poor health habits contribute most to aging. Osteoporosis is a good example.
Skin loses elasticity and becomes thinner with age, resulting in sagging and wrinkling.
Fewer sweat glands are present, so temperature regulation is less efficient. The heart shrinks with age, and fatty deposits clog arteries. Lungs lose some elasticity, so ventilation is reduced. A reduced blood supply to the kidneys results in the kidneys becoming smaller and less efficient. The digestive tract may lose muscle tone but still absorbs nutrients efficiently.