Growth Hormone (Somatotropin)

Growth hormone is a naturally released anabolic hormone by the pituitary gland. It promotes muscle growth and the breakdown of body fat for energy. Unfortunately it is greatly reduced after the age of about 20

Physiologic Effects of Growth Hormone

A critical concept in understanding growth hormone activity is that it has two distinct types of effects:

•    Direct effects are the result of growth hormone binding its receptor on target cells. Fat cells have growth hormone receptors. Growth hormone stimulates fat cells 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-I (IGF-I), 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.
Keeping this distinction in mind, we can discuss two major roles of growth hormone and its minion IGF-I in physiology.

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