delta cell

The delta cell is the islet's local referee, calling time-out on its noisier neighbors. It secretes somatostatin, a hormone whose name literally means it stops growth-hormone release, but inside the islet its main job is to dampen the secretion of both insulin and glucagon. Delta cells are far less numerous than beta or alpha cells.

Somatostatin acts mostly by paracrine signaling, meaning it diffuses the short distance to its neighbors rather than traveling through the bloodstream. By restraining both the brake (insulin) and the accelerator (glucagon), the delta cell helps keep hormone output from swinging too wildly and fine-tunes the timing and amplitude of islet responses.

Delta cells have long, branching projections that let one cell influence many others, somewhat like a neuron. Research increasingly views them as integrators that sense glucose, neural input, and other islet hormones, then set the overall gain of the islet — though their exact contribution in human disease is still being worked out.