Non-GIT hormones may influence growth and development of the GIT. GIT hormones may influence
activities outside of the GIT. E.g. ghrelin is secreted by the endocrine cells of the stomach, but rarely acts
in the GIT, it instead travels to the hypothalamic “feeding centre” to influence appetite. Leptin is
secreted by adipose tissue, which acts on the brain to suppress appetite.
At the same time, GIT hormones may play an important role in the regulation of the GIT itself. First
hormone identified is secretin. The diffuse endocrine system (DES) is the largest and the most diversified
endocrine system in the body. 5 of the most important GI hormones are gastrin, CCK, secretin, GIP and
3 ways of endocrine regulation: Autocrine (affect self). Paracrine (affect nearby). And endocrine itself,
involving blood transport.
Gut Regulatory Hormones = mostly peptides
Released from the mucosa into the portal blood, which then goes to the liver, and via the circulation,
reaches its target. Could have multiple targets. They are capable of interacting with each other and the
neurotransmitters. They could interact synergistically (potentiate each other), or antagonistically
(against each other).
Motility – the physical act of breaking down the food and pushing it further down the tract. The
beginning and end of the tract are skeletal in nature, while the midsection is smooth. The propulsion of
the food has 2 factors controlling it, the gradients of pressure and the variation of resistance.
Coordinated contractions of muscular elements in the wall of the GIT, being segmented, a shifting
contraction to force food down and mix the food. Segmentation pushes on two ends and then in the
middle. Peristalsis is a continuous push down the tract. When not eating, all sphincters are closed, when
eating, the sphincters open reflexively anticipating the food. When food is past, it closes tightly to
prevent reflux. Normally, flow is slow, aboral (away from mouth), and meets little to no resistance.
Deglutition (swallowing): A continuous process. 3 phases: oral, pharyngeal and the esophageal phases.