Final answer:
Atrophy refers to the decrease in size or wasting away of tissue, often resulting from diseases, aging, or physical inactivity. Conditions like cancer and AIDS can cause cachexia, leading to muscle atrophy, while aging leads to sarcopenia, a gradual decline in skeletal muscle mass that is irreversible.
Step-by-step explanation:
A decrease in size or wasting away of tissue is known as atrophy. Atrophy can be caused by conditions such as cancer and AIDS, which can induce a body wasting syndrome named cachexia. Aside from diseases, other factors like congestive heart disease, liver diseases, physical inactivity, and the natural process of aging can also lead to muscle atrophy. This decline in muscle tissue is specifically referred to as sarcopenia in the context of aging, where there is a gradual decrease in the ability to maintain skeletal muscle mass.
The exact cause of sarcopenia is not entirely known, but it may involve a decrease in the sensitivity to growth factors needed to maintain muscle mass, and the normal reduction of muscle fibers' capacity to regenerate. Consequently, muscle atrophy leads to a decrease in muscle strength. This can significantly affect an individual's quality of life, particularly in older age, as it can result in a reduced capacity for posture, mobility, and overall muscle function.