Acromegaly 课文.doc

Acromegaly When GH excess occurs in adulthood or after the epiphyses of the long bones have fused，a condition known as acromegaly developed. Acromegaly is a chronic and debilitating disorder of body growth and metabolic derangements in the adult caused by excess levels of GH. The mean age at the time of diagnosis is about 40 in men and 45 in women. Most cases of acromegaly are caused by pituitary adenoma. The disorder usually has an insidious onset，and symptoms are often present for a considerable period of time before a diagnosis is made. When the production of excessive GH occurs after the epiphyses of the long bones have closed, as in the adult, the person can not grow taller, but the soft tissues continue to grow. Enlargement of the small bones of the hands and feet and in the membranous bones of the face and skull results in pronounced enlargement of the hand and feet, a broad and bulbous nose, a protruding lower jaw, and a slanting forehead. The teeth become splayed, causing a disturbed bite and difficulty in chewing. The cartilaginous structures in the larynx and respiratory tract also become enlarged, resulting in a deepening of the voice and tendency to develop bronchitis. Vertebral changes often lead to kyphosis, or hunchback. Bone overgrowth often leads to arthralgia and degenerative arthritis of the spine, hips, and knees. Virtually, every organ of the body is increased in size. Enlargement of the heart and accelerated atherosclerosis may lead to an early death. The metabolic effects of excess levels of GH include alterations in fat and carbohydrate metabolism. Increased levels of GH have a diabetogenic effect. GH acts as an insulin antagonist; in excess, it increases carbohydrate utilization and it impairs glucose uptake into cells. This leads to glucose intolerance, which, in turn, stimulates the beta cells of the pancreas to produce additional insulin. In addition, GH also increases the ability of the beta cells to respond to insulinogenic stimuli.