tillväxthormonaxelns

The growth hormone axis, also known as the somatotropic axis, is a complex endocrine system primarily regulated by the hypothalamus and the pituitary gland. This axis plays a crucial role in childhood growth and development, as well as maintaining metabolic homeostasis in adults. The central component of this axis is growth hormone (GH), also called somatotropin.

The hypothalamus, specifically the arcuate nucleus, produces two key peptides that control GH release from the anterior pituitary: growth hormone-releasing hormone (GHRH) and somatostatin. GHRH stimulates the pituitary to secrete GH, while somatostatin inhibits it. These hypothalamic peptides are released in a pulsatile manner, leading to pulsatile GH secretion from the pituitary.

GH, once released into the bloodstream, exerts its effects through two main mechanisms. Firstly, it directly acts on various tissues, influencing cellular metabolism, protein synthesis, and lipolysis. Secondly, and perhaps more significantly for growth, GH stimulates the liver and other tissues to produce insulin-like growth factor 1 (IGF-1). IGF-1 then mediates many of the growth-promoting effects of GH, particularly on bone and cartilage.

The activity of the growth hormone axis is tightly regulated by feedback mechanisms. High levels of GH and IGF-1 typically inhibit the release of GHRH and GH from the pituitary, creating a negative feedback loop that maintains hormonal balance. Conversely, low levels of GH and IGF-1 can stimulate their release. This intricate system ensures that GH is secreted appropriately to support growth and metabolism throughout life.