Several pathological conditions are associated with abnormal GH secretion. In general, the causes for hypersecretion or hyposecretion of GH involve tumors in the hypothalamus or the pituitary, the synthesis of structurally abnormal GH, the inability of the liver to produce somatomedins, or the lack of receptor molecules in the target cells.

Chronic hyposecretion of GH in infants and children leads to dwarfism, in which the stature is short because of delayed bone growth. However, the bones usually have a normal shape. In contrast to the dwarfism caused by hyposecretion of thyroid hormones, theses dwarfs exhibit normal intelligence. Other symptoms resulting from the lack of GH include mild obesity and retard development of adult reproductive functions. Two types of dwarfism result from a lack of GH secretion: (12) one that occurs in approximately two thirds of the cases, in which GH and other anterior pituitary hormones are secreted in reduced amounts; and (2) one that occurs in approximately one third of the cases, in which only a reduced amount of GH is observed and normal reproduction can occur. No obvious pathology is associated with hyposecretion of GH in adults, although there is some evidence indicating that lack of GH can lead to reduced bone mineral content in adults.

The gene responsible for determining the structure of GH has been transferred successfully from human cells to bacterial cells, which produce GH that is identical to human GH. The GH produced in this fashion currently is available to treat patients who suffer from a lack of GH secretion.

Chronic hypersecretion of GH leads to giantism or acromegaly, depending on whether the hypersecretion occurs before or after complete ossification of the epiphyseal plates in the skeletal system. Chronic hypersecretion of GH before the epiphyseal plates have ossified causes exaggerated and prolonged growth in long bones, resulting in giantism. Some individuals have grown to 8 feet tall or more.

In adults chronically elevated GH levels result in acromegaly. No increase in height occurs because of the ossified epiphyseal plates. The condition does result in an increased diameter of fingers, toes, hands, and feet; the deposition of heavy bony ridges above the eyes; and a prominent jaw. The influence of GH on soft tissues results in a bulbous and broad nose, and enlarged tongue, thickened skin, and sparse subcutaneous adipose tissue. Nerves frequently are compressed as a result of the proliferation of connective tissue. Because GH spares glucose usage, chronic hyperglycemia results, frequently leading to diabetes mellitus and the development of severe atherosclerosis. Treatment for chronic hypersecretion of GH often involves surgical removal or irradiation of a GH-producing tumor.

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