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growth hormone or somatotropin (sōmătˌətrōˈpən), glycoprotein hormone released by the anterior pituitary gland that is necessary for normal skeletal growth in humans (see protein). Evidence suggests that the secretion of human growth hormone (HGH) is regulated by the release of certain peptides by the hypothalamus of the brain. One such substance, called somatostatin, has been shown to inhibit the secretion of HGH. HGH is known to act upon many aspects of cellular metabolism, but its most obvious effect is the stimulation of the growth of cartilage and bone in children.
See also auxins (plant growth hormones).
Role in Dwarfism and Gigantism
A deficiency of growth hormone secretion before puberty (by the end of which the synthesis of new bone tissue is complete) results in pituitary dwarfism. Pituitary dwarfs, who can be as little as 3 to 4 ft (91–122 cm) tall, are generally well proportioned except for the head, which may be relatively large when compared to the body (this relationship of head to body is similar to that of normal children). Unlike cretins, whose dwarfism is caused by a deficiency of thyroxine, pituitary dwarfs are not mentally retarded; they are often sexually immature. They can be treated by injections of synthetic growth hormone, either somatrem or somatropin, which are produced by genetically engineered bacteria.
An excess of growth hormone in children results in gigantism; these children grow to be over 7 ft (213 cm) in height and have disproportionately long limbs. Excess growth hormone produced after puberty has little effect on the growth of the skeleton, but it results in a disease affecting terminal skeletal structures known as acromegaly.
Other Medical Uses
an adenohypophyseal hormone that accelerates the longitudinal growth of an organism’s bones and the organism’s overall body growth. It also helps regulate carbohydrate, lipid, and protein metabolism.
Growth hormone is synthesized by acidophilic cells of the anterior pituitary and secreted into the blood, where it is rapidly broken down. Human growth hormone is a protein with a molecular weight of 21,500. Its polypeptide chain consists of 191 amino-acid residues and contains two disulfide bridges. The primary structure of human, sheep, and ox growth hormone has been established.
The chemical structure of growth hormone has changed in different animals during the course of evolution, and the hormone has differentiated according to species. In man and sheep, for example, the hormones differ by a sequence of 70 amino-acid residues, which constitute more than one-third of the protein molecule. Therefore, animal growth hormone does not stimulate human growth, whereas human growth hormone is able to stimulate the growth of experimental animals (monkey growth hormone is closest to human growth hormone).
Increased secretion of growth hormone by the pituitary gland at an early age accelerates growth and causes gigantism. At a later age such increased secretion leads to acromegaly. A decrease in secretion results in hypophyseal dwarfism. This disease when detected in childhood responds to treatment by injections of growth hormone.
REFERENCESinitsina, A. L., and Iu. M. Keda. “Sovremennye predstavleniia o strukture i funktsii gormona rosta.” In the collection Sovremennye voprosy endokrinologii, fasc. 4. Moscow, 1972.
IU. A. PANKOV