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Lecture 17

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McGill University
PHGY 210
Ann Wechsler

Lecture 17 Hormonal Regulation 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 VIP. 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. Oral phase:
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