When is hgh secreted

Growth hormone does seem to have a direct effect on bone growth in stimulating differentiation of chondrocytes. IGF-I also appears to be the key player in muscle growth. It stimulates both the differentiation and proliferation of myoblasts.

It also stimulates amino acid uptake and protein synthesis in muscle and other tissues. Growth hormone has important effects on protein, lipid and carbohydrate metabolism.

In some cases, a direct effect of growth hormone has been clearly demonstrated, in others, IGF-I is thought to be the critical mediator, and some cases it appears that both direct and indirect effects are at play. 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 secretion is also part of a negative feedback loop involving IGF-I.

High blood levels of IGF-I lead to decreased secretion of growth hormone not only by directly suppressing the somatotroph, but by stimulating release of somatostatin from the hypothalamus. Growth hormone also feeds back to inhibit GHRH secretion and probably has a direct autocrine inhibitory effect on secretion from the somatotroph. Integration of all the factors that affect growth hormone synthesis and secretion lead to a pulsatile pattern of release. Basal concentrations of growth hormone in blood are very low.

In children and young adults, the most intense period of growth hormone release is shortly after the onset of deep sleep. States of both growth hormone deficiency and excess provide very visible testaments to the role of this hormone in normal physiology.

Such disorders can reflect lesions in either the hypothalamus, the pituitary or in target cells. In: Lindsten J, editor.

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Regulation of insulin secretion in human pancreatic islets. Annu Rev Physiol — Calcium signaling in pancreatic beta-cells in health and in type 2 diabetes. Cell Calcium 56 5 — In humans, these interactions result in a pattern of volleys of GH-secretory pulses with intervening periods of relative secretory quiescence. The amplitude and frequency of GH-secretory pulses are regulated by a complex array of external and internal stimuli including age, gender, menstrual cycle phase, pubertal status, nutrition, sleep, body composition and exercise.

Changes in plasma concentrations of gonadal hormones, insulin and insulin-like growth factor-I likely mediate the effects of several of these factors. A greater understanding of the physiology of GH secretion will enable the development of future strategies to enhance GH secretion in GH-deficient states including the use of GH secretagogues and modification of nutrition and exercise habits.