Growth hormone

Growth hormone is an important regulator of growth and cell reproduction and a deficiency in this hormone gives rise to growth failure, reduced muscle and bone mass and many other problems relating to development of the body. In extreme cases, pituitary dwarfism can occur. Too much growth hormone can result in a pituitary tumour which causes gigantism if the tumour occurs during childhood.

Growth hormone is synthesised by somatotroph cells of the anterior pituitary gland and its synthesis is stimulated by the binding of growth hormone-releasing hormone to the GHRH receptor.This receptor is G protein-coupled receptor, so when GHRH binds, adenyly cyclase is activated which increase intracellular levels of cAMP. As a result, gene transcription is stimulated and growth hormone is synthesised. The release of stored GH is also activated via the G protein messenger pathway as increased levels of cAMP opens calcium channels causing intracellular calcium levels to rise. When this happens, the release of growth hormone from the samatotroph cells is stimulated.The growth hormone-releasing hormone is released from the hypothalamus when its nuclei are stimulated by neurones in response to factors such as sleep, fasting, puberty and strenuous exercise.

The growth hormone itself is a 191 amino acid long polypeptide encoded by a gene on the long arm of chromosome 17 with a weight of 22-kDa. 

References:

Walter F. Boron, 2009. Medical physiology. 2nd ed. Philadelphia. Saunders Elsevier

Tanner JM. 1972. Human Growth Hormone. Nature. (5356), pp.433-9.