Gut Physiology
L. vagus n (anterior) gives hepatic branch, R (posterior) gives celiac branch and the 'criminal nerve of Grassi' which if undivided can keep high acid levels post vagotomy
Chief Cells produce pepsinogen (-> pepsin) which initiates proteolysis
Parietal cells produce H+ and intrinsic factor which binds B12, and is absorbed in terminal ileum
Acetylcholine (Ach), Gastrin, and Histamine are main stimuli for H+ production
Ach (vagus) and Gastrin activate PIP, DAG to increase Ca, activate protein Kinase C which increases HCL production
Histamine acts on parietal cell via cAMP (H for Happy cAMPer) to increase HCL production
Gastrin produced by antral G cells (why antrectomy helpful); inhibited by H+ in duodenum. Stimulated by amino acids, Acetylcholine
Omeprazole blocks H/K ATPase of parietal cell
Somatostatin inhibits gastrin, insulin, secretin, Ach; decreases pancreatic/biliary output
-stimulated by acid in duodenum
Proximal vagotomy abolishes receptive relaxation which increases liquid emptying; no chance for solids
Truncal vagotomy also increases emptying of solids when pyloroplasty done. TV decreases basal acid by 80%
Most common symptom post vagotomy is diarrhea (35%)
-dumping syndrome is 10%, early due to hyperosmotic load, fluid shift; late due to increased
insulin, decreased glucose
-very rare (1%) that dumping unresponsive to dietary measures
Enterokinase activates trypsinogen to trypsin which then activates other enzymes of digestion
CCK: from intestinal mucosa
-contracts gallbladder
-relaxes sphincter of Oddi
-increases pancreatic enzyme secretion
Secretin: primary stimulus of pancreatic bicarb secretion, high flow rate=high bicarb, low Cl
-slow flow allows HCO3/Cl exchange so low bicarb, high Cl concentration
Enteroglucagon: increases small bowel mucosal hypertrophy, adaptation after small bowel resection
Peptide YY: released from terminal ileum with mixed meal, inhibits acid secretion
-"ileal brake"
Bile: 80% bile salts, 15% lecithin, 5% cholesterol
-stones form if increased cholesterol or decreased salts or lecithin
-gallbladder concentrates bile by active reabsorption of Na, Cl; H2O then follows
-bile pool 5g, recirculated q4 hours, lose .5g daily (10%)
Primary bile acids: Cholic acid, Chenodeoxycholic acid
Secondary (formed by intestinal bacteria): deoxycholic acid and lithocholic acid
MMC: interdigestive motility; 90 minute cycles; starts in stomach, goes to TI
-Phase 1 quiescence, II gallbladder contraction, III peristalsis, IV subsiding electric activity
-Motilin is key stimulatory hormone (erythromycin is prokinetic by stimulating motilin receptor)
Jejunum absorbs most Na and H2O (paracellular), more permeable than ileum