Question

The human growth hormone, somatotropin, is a peptide hormone that stimulates growth, especially in childhood. It strengthens bone, increases muscle mass, reduces glucose uptake by the liver and promotes the breakdown of body fat.

Outline the mode of action of somatotropin on target cells.

Accepted Answer

Mode of action of somatotrophin

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 supresses their ability to take up and accumulate circulating lipids.

Indirect effects are mediated primarily by a insulin like growth factor (IGF-1), 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.

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. It also stimulates amino acid uptake and protein synthesis in muscle and other tissues.

Once released into the circulation, GH binds and activates the cell-surface GHR, as well as the related prolactin receptor in target tissues such as liver, muscle, bone, and adipose tissue . It is the key regulator of insulin-like growth factor 1 (IGF1), which is secreted from target tissues, particularly the liver. Increased serum GH and IGF1 produce feedback loops that lead to inhibition of GHRH, release of somatostatin, and consequently inhibition of GH secretion from the pituitary.

The human growth hormone, somatotropin, is a peptide hormone that stimulates growth, especially in childhood. It strengthens bone, increases muscle mass, reduces glucose uptake by the liver and promotes the breakdown of body fat.

Outline the mode of action of somatotropin on target cells.

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