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somatotropin(sōmăt'ətrō`pən), glycoprotein hormonehormone,
secretory substance carried from one gland or organ of the body via the bloodstream to more or less specific tissues, where it exerts some influence upon the metabolism of the target tissue.
..... Click the link for more information. released by the anterior pituitary glandpituitary gland,
small oval endocrine gland that lies at the base of the brain. It is sometimes called the master gland of the body because all the other endocrine glands depend on its secretions for stimulation (see endocrine system).
..... Click the link for more information. that is necessary for normal skeletal growth in humans (see proteinprotein,
any of the group of highly complex organic compounds found in all living cells and comprising the most abundant class of all biological molecules. Protein comprises approximately 50% of cellular dry weight.
..... Click the link for more information. ). Evidence suggests that the secretion of human growth hormone (HGH) is regulated by the release of certain peptides by the hypothalamushypothalamus
, an important supervisory center in the brain, rich in ganglia, nerve fibers, and synaptic connections. It is composed of several sections called nuclei, each of which controls a specific function.
..... Click the link for more information. 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 auxinsauxin
, plant hormone that regulates the amount, type, and direction of plant growth. Auxins include both naturally occurring substances and related synthetic compounds that have similar effects. Auxins are found in all members of the plant kingdom.
..... Click the link for more information. (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 thyroxinethyroxine
, substance secreted by the thyroid gland. The hormone thyroxine forms by combining the amino acid tyrosine with iodine. Complexed to a protein, it is stored in the follicle stems between thyroid cells.
..... Click the link for more information. , 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 acromegalyacromegaly
, adult endocrine disorder resulting from hypersecretion of growth hormone produced by the pituitary gland. Since the bones cannot increase in length after full growth is attained, there is a disproportionate thickening of bones, predominantly in the skull and small
..... Click the link for more information. .
Other Medical Uses
HGH has been used with some success to combat the weight loss and general wasting characteristic of AIDS and cancer. It is used illegally by bodybuilders and athletes to increase muscle mass. Controversy surrounds its use in normal children who simply want to be taller. In addition, a 1990 medical study that reported the reversal of many of the physiological effects of aging with regular injections of HGH has created a lucrative black market for it and has prompted funding of further trials. There has been no conclusive evidence, however, to support the use of HGH as an anti-aging treatment, and it can cause serious side effects, including diabetes, in older adults.
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