Growth-hormone-releasing-hormone (GHRH) is a peptide hormone that is released from the arcuate nucleus located in the hypothalamus. The release of GHRH activates the discharge of growth hormones into the bloodstream, which act to stimulate growth in the body, particularly in long bones such as those found in the arms and legs. Secretion of growth hormone or somatotrophin is inhibited or repressed by a growth-hormone-inhibiting hormone, also called somatostatin.
The hypothalamus is located at the base of brain below the thalamus and is involved in many different functions. It acts to regulate temperature and is involved in metabolism, reproduction, and aggression. Another function includes controlling hormone release in the endocrine system. The endocrine system is made up of glands that secrete hormones into the bloodstream, enabling those hormones to be dispersed throughout the body. Part of the endocrine system is the pituitary gland, which is connected to and controlled by the hypothalamus.
Hormones are similar to neurotransmitters or neuromodulators because they produce responses by stimulating receptors located on or inside nerve cells. The difference is that they work over longer distances within the body. When a receptor molecule is stimulated by the presence of a hormone, it results in a particular physiological response. Hormone release in the pituitary gland contributes to body growth, predominately the growth of long bones.
Growth hormone is controlled by GHRH, which is a 44-amino-acid peptide that is created by neurons in the arcuate nucleus found in the hypothalamus. When GHRH is released, it is moved from the hypothalamus into the anterior pituitary gland via a hypothalamic-pituitary system, resulting in a release of growth hormone from somatotrophs into the bloodstream. Somatotrophs are membranous cells found in the anterior pituitary that specifically produce growth hormone.
Somatostatin, or growth-hormone-inhibiting-hormone (GHIH), is a 14-amino-acid peptide that inhibits the release of growth hormone in the body. It is extensively spread throughout the central nervous system, but the inhibiting nerve cells are located in the periventricular nucleus in the hypothalamus. Many neurons located in the arcuate nucleus contain somatostatin, which also inhibits prolactin release, a hormone that causes mammary glands in women to grow before and after giving birth.
Release of growth hormone within the body causes cell division and results in the development of body tissues. Growth hormone has a significant effect on body growth, particularly during perinatal growth and throughout adolescence. Throughout these periods, variables such as fasting, stress, and exercise all increase growth hormone release, which act to make fatty acids into energy.