Atrophy is a pathological concept that refers to the reduction in size of parenchymal cells, tissues or organs that have developed normally, and can be divided into physiological atrophy and pathological atrophy. Physiological atrophy refers to the shrinkage of many tissues and organs of the body with age, such as the femoral and reproductive systems, which atrophy after menopause, and the thymus, which atrophies after puberty. Pathological atrophy is commonly seen in malnutrition atrophy, such as patients with advanced malignancy, or various atrophies caused by long-term inadequate protein intake and excessive consumption, such as muscle atrophy, cerebral atrophy after cerebral arteriosclerosis, and compression atrophy, which is commonly seen in renal atrophy due to urinary tract obstruction and disuse atrophy. There is also hypofunction caused by prolonged non-working of major organs, such as muscle atrophy in sedentary patients, and endocrine atrophy, such as adrenal atrophy due to pituitary ischemia.