Gastrointestinal function is regulated by two chemically distinct classes of signaling molecule that act alongside neural control: endocrine hormones, secreted by specialized enteroendocrine cells into the bloodstream to act on distant targets, and paracrine mediators, released locally to act on neighboring cells within the gut wall. Five canonical GI hormones — cholecystokinin, gastrin, gastric inhibitory peptide, motilin, and secretin — each originate from a defined cell type with a characteristic anatomical distribution along the stomach and small intestine, and each exerts a specific effect on secretion or motility; four principal paracrine molecules — histamine, nitric oxide, prostaglandins, and somatostatin — modulate acid secretion, mucosal protection, blood flow, and smooth-muscle tone. This material belongs to gastrointestinal physiology within the broader discipline of systems physiology, where the general principle is that digestive secretion and motility are coordinated by chemical messengers whose site of release, target distance, and target cell type together determine their physiological role.
Gastrointestinal function is regulated by two chemically distinct classes of signaling molecule that act alongside neural control: endocrine hormones, secreted by specialized enteroendocrine cells in…