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Growth hormone is a protein hormone of about 190 amino acids that is synthesized and secreted by cells called somatotrophs in the anterior pituitary. Growth hormone is also of considerable interest as a drug used in both humans and animals.
Physiologic Effects of Growth Hormone
A critical concept in understanding growth hormone activity is that it has two distinct types of effects:
Direct effects are the result of growth hormone binding its receptor on target cells. Fat cells (adipocytes), for example, have growth hormone receptors, and growth hormone stimulates them to break down triglyceride and suppresses their ability to take up and accumulate circulating lipids.
Indirect effects are mediated primarily by an insulin-like growth factor-I (IGF-I), a hormone that is secreted from the liver and other tissues in response to growth hormone. A majority of the growth promoting effects of growth hormone is actually due to IGF-I acting on its target cells.
Effects on Growth
Growth is a very complex process, and requires the coordinated action of several hormones. The major role of growth hormone in stimulating body growth is to stimulate the liver and other tissues to secrete IGF-I. IGF-I stimulates proliferation of chondrocytes (cartilage cells), resulting in bone growth. Growth hormone does seem to have a direct effect on bone growth in stimulating differentiation of chondrocytes.
Growth hormone has important effects on protein, lipid and carbohydrate metabolism.
Protein metabolism: In general, growth hormone stimulates protein anabolism in many tissues.
Fat metabolism: Growth hormone enhances the utilization of fat by stimulating triglyceride breakdown and oxidation in adipocytes.
Carbohydrate metabolism: Growth hormone is one of a battery of hormones that serves to maintain blood glucose within a normal range. Somewhat paradoxically, administration of growth hormone stimulates insulin secretion, leading to hyperinsulinemia.
Control of Growth Hormone Secretion
Production of growth hormone is modulated by many factors, including stress, exercise, nutrition, sleep and growth hormone itself. However, its primary controllers are two hypothalamic hormones and one hormone from the stomach:
Growth hormone-releasing hormone (GHRH) is a hypothalamic peptide that stimulates both the synthesis and secretion of growth hormone.
Somatostatin inhibits growth hormone release in response to GHRH and to other stimulatory factors such as low blood glucose concentration.
Ghrelin binds to receptors on somatotrophs and potently stimulates secretion of growth hormone.
Growth hormone secretion is also part of a negative feedback loop involving IGF-I. Basal concentrations of growth hormone in blood are very low. States of both growth hormone deficiency and excess provide very visible testaments to the role of this hormone in normal physiology. Clinically, deficiency in growth hormone or defects in its binding to receptor are seen as growth retardation or dwarfism.
Giantism is the result of excessive growth hormone secretion that begins in young children or adolescents.
Acromegaly results from excessive secretion of growth hormone in adults, usually the result of benign pituitary tumors. Pharmaceutical and Biotechnological Uses of Growth Hormone
In years past, growth hormone purified from human cadaver pituitaries was used to treat children with severe growth retardation. Human growth hormone is commonly used to treat children of pathologically short stature. Similarly, growth hormone has been used by some to enhance atheletic performance. Parents that request growth hormone therapy for children of essentially-normal stature are clearly misguided.
The role of growth hormone in normal aging remains poorly understood, but some of the cosmetic symptoms of aging appear to be amenable to growth hormone therapy. Growth hormone is currently approved and marketed for enhancing milk production in dairy cattle. FDA (Food and Drug Administration) has approved human growth hormone therapy only for children with growth hormone deficiency. Basically human growth hormone is produced and secreted by pituitary gland located in the center of brain. Sometime pituitary gland produces less amount of human growth hormone that causes many problems in children. It is recommended to use human growth hormone to treat the children with following disorder
Stunned growth
Many human growth hormone products are available in market to treat children with human growth hormone deficiency. Human growth hormone injections are one of them which help children in growing. Human growth hormone injections are effective as they are absorbed into bloodstream directly. Medical professional prescribe human growth hormone injection after proper diagnosis to children with human growth hormone deficiency. It is illegal to use human growth hormone injection without prescriptions.
However human growth hormone injection therapy is very expensive treatment. Heart problem, renal failure, thyroid problem are the possible causes of undergrowth of children other than human growth hormone deficiency.
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