Insulin

Insulin is the pancreatic hormone that signals nutrient abundance: it tells tissues to absorb glucose, store energy, and grow, and its signaling pathway is the evolutionary ancestor of the aging-control systems studied in worms and flies.

Function

Insulin is secreted by pancreatic β-cells when blood glucose rises after a meal. It binds the insulin receptor, a tyrosine kinase that recruits IRS proteins and activates two main routes: the PI3K–AKT arm, which moves GLUT4 transporters into muscle and fat cell membranes and drives glycogen and lipid storage; and the MAPK arm, which drives growth. Between meals, insulin falls and the body mobilizes stores — the hormone’s absence