Human growth hormones play an important role in normal human growth and development. The major human growth hormone is a protein made up of 191 amino acids, the building blocks of proteins. The production of this protein is controlled by two other hormones secreted by the hypothalamus: growth hormone releasing hormone (GHRH), which controls secretion of hGH; and growth hormone-inhibiting hormone (GHIH), which inhibits secretion of hGH. All healthy individuals have measurable levels of hGH throughout life, but there are two notable growth spurts, one at birth and the other at puberty, and hGH plays a vital role at each time. The most obvious effect of hGH is on linear skeletal growth (height), but metabolic effects of hGH (the results of hGH activity in the body) on muscle, the liver, and fat cells are a critical part of its function. When any question arises about growth or development, pediatricians may investigate the levels of the major growth hormone hGH, its receptors and stimulants, the glands that produce the hormones, and the complex hormone interactions that control normal development.Somatotropin (hGH) is secreted by somatotropes in the anterior pituitary gland. It is typically secreted during sleep , with peak release occurring around 10 p.m., midnight, and 2 a.m. Most of the effects of hGH are mediated by other hormones, including the somatomedins, IGH-I (somatomedin C) and IGH-II, which are insulin-like growth hormones that also influence linear growth, and the two hypothalamic hormones (GHRH and GHIH) that regulate hGH by responding to changes in the individual's blood sugar (glucose) and protein levels. When blood glucose levels fall, GHRH triggers the secretion of stored hGH. As blood glucose levels rise, hGH secretion is turned off by GHIH activity. Increases in blood protein levels trigger a similar response. This feedback loop, along with the effects of eating and exercise , is responsible for the fluctuating levels of hGH throughout the day. ...
