growth hormone

Growth hormone is the body's main signal to grow taller during childhood, like a foreman telling the construction crew of your bones and tissues to keep building. It is made in the front part of the pituitary gland, a pea-sized organ hanging beneath the brain.

Chemically it is a protein hormone of about 191 amino acids. It is released in bursts, especially during deep sleep and exercise, rather than at a steady level. Its release is turned up by GHRH from the hypothalamus and turned down by somatostatin, so the brain holds two opposing levers over how much circulates.

Growth hormone has two kinds of effects. Many of its growth-promoting actions are indirect: it travels to the liver and triggers the release of IGF-1, which then drives bone and muscle growth. But growth hormone also acts directly on tissues to raise blood glucose, break down fat, and oppose insulin, which is why it matters for metabolism and not just height.

A caveat worth remembering: more growth hormone does not simply mean more growth. Once the growth plates of the long bones have fused after puberty, extra growth hormone can no longer add height; instead it thickens bone and soft tissue, producing the disfiguring features of acromegaly in adults.