Insulin signallingInsulin signaling

Insulin signalling begins when insulin binds its receptor on a cell surface, setting off a cascade through insulin receptor substrate proteins and PI3K/Akt that ultimately moves GLUT4 transporters to the cell membrane, letting glucose in.

It matters because breakdown at any point in that chain produces insulin resistance: insulin is present, but the cell no longer responds properly, so the pancreas secretes more to compensate. Sustained, that is the road to type 2 diabetes.

In practice muscle contraction recruits GLUT4 through a separate, insulin-independent route. That is why exercise lowers blood glucose even in people whose insulin signalling is impaired, and why it is such a powerful intervention in prediabetes and type 2 diabetes.