GI Physiology Review

GI Physiology ReviewLecture 2:

-G protein coupled receptors: Has seven transmembrane domains, olfaction is mediated by this type of receptor

-APUD cells [Amine Precursor Uptake and Decarboxylate]: unrelated endocrine cells found throughout the body; synthesize serotonin, epi, norepi, neurotensin, and dopamine

-derived from neural crest cells that migrate to the foregut

-adsorb and decarboxylate monoamines to form biogenic amines

-GASTRIN:

-Gastrin 17 is released from G cells in the antrum of the stomach

-Gastrin 34 is located in the duodenum

-Gastrin binds to CCKb receptor

-Released in response to proteins/amino acids, gastric distention, or by CNS

-Inhibited when the ph is less than 3.5, somatostatin

-Antagonized by VIP/Secretin

-Promotes Acid and Intrinsic Factor secretion, promotes antral motility, smooth muscle contraction of LES, vasodilation, and growth

-Is a hormone that is released in response to feeding

-Cholecystekinin:

-acts via CCKA receptors

-Released from I cells in the duodenum, nerve fibers from small intestine and pancreas

-Released in response to fat, proteins

-inhibited by somatostatin

-Function: Stimulates GB contraction, inhibits gastric emptying, promotes pancreatic secretion, vasodilator, exocrine pancreas growth, relaxes the sphincter of oddi

-Secretin + CCK have synergistic effects

-SECRETIN:

-Released from the S cells in the duodenum and jejunum

-released in response to duodenal acidification and bile salts

-inhibited by VIP (at level of receptor) and Somatostatin

-Function: Releases bicarbonate by pancreatic ductular epithelium, increase water and bicarbonate release by biliary epithelium, decrease water absorption in the GB, vasodilator, decreases lower esophageal sphincter pressure

-SOMATOSTATIN:

-Released from D cells of the pancreas and the stomach and small intestine

- Highest during migratory motor complexes, released in response to protein, fat, bile, motilin, CCK, glucagons, GRP, secretin

-Inhibited by Gastrin and cholinergics

-Function: Decreases growth hormone and TSH release from brain

Decreases acid, pepsin, gastrin in stomach

Decreased growth, glucagon, insulin, CCK, and exocrine secretions

Inhibits GB contraction and fluid secretion

Antagonizes motilin and decreases water and electrolyte secretion in small intestine

-Negative regulator of the GI tract

-Can be used for treating chronic diarrhea

Glucagon: Secreted from L cells in the intestine and from the pancreas

-Released in response to intestinal glucose

-Inhibited by glucose in pancreas, SST

-Function: Gluconeogenesis, lipolysis, decreased acid, decreased LES

Ghrelin: Homologous to motilin

-Released from stomach A like oxyntic cells, duodenum, ileum, cecum, placenta

-Inhibited by H Pylori

-Stimulates Growth Hormone release (better than GHRF)

-Increases prolactin, ACTH, cortisol, aldosterone release

-increases apetite and food intake

-increases blood glucose levels, somatostatin, PP

-decreases blood pressure and increases Cardiac Output

-increases gastric acid secretion, gastric emptying, ulcer protective

-increases tumor cell proliferation

- increases anxiety and memory retention, increases slow wave sleep

-Ghrelin levels are low in the obese

-weight loss associated with increased ghrelin secretion (90% weight loss regained within one year)