Digestion

Structure of the wall of the GI tract

Sphincters

Gastric emptying

Vomiting

Exocrine glands

Have ductsEpithelium is

continuous w/ body surface

Ex: Salivary, gastric glands, pancreas, bile glands in liver, sweat glands

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/ExocrineGlands.html

Wall of the GI Tract

Mucous Membrane Epithelium (varies) Lamina propria

(Connective tissue) Muscularis Mucosa

(smooth muscle)

Submucosa

Muscularis Externa, Serosa

Muscularis Externa: 2 layers of smooth muscle Inner circular fibers Outer longitudinal fibers Neural network in between

Enteric nervous system

Serosa: outermost layer Connective tissue Squamous cells

Muscularis Externa Layers

Sphincters

UES LES Pyloric Ileocecal Internal anal External anal

GI secretions

Gastric: Gastrin: gastric juice secretion

Enterogastrones: Secretin: bicarbonate from pancreas• CCK: • bile (contractions from gall bladder) in response

to amino, fatty acids• pancreatic enzymes

Gastric Emptying

Needs to be mediated so rate of emptying into the small intestine isn’t greater than rate of small intestine processing

Presence of acid in the duodenom secretin closes pyloric sphincter, stimulates secretions of the pancreas

Presence of fat: release of CCK closes pyloric sphincter

Presence of peptides/amino acids: release of gastrin closes pyloric sphincter

Yaking, spewing, blowing chunks, hurling, etc. (vomiting)

Reflex, expulsion of stomach/duodenal contents

Retching: contents forced into esophagus, not up to pharynx

Reverse peristalsisPyloric sphincter relaxes

Yaking (continued)

“vomiting center” in medulla signaled by:Distension of stomach, pressure in the back of the

throatInjury to urogenital areaDizziness

Emetics: stimulate stomach/duodenum receptors to induce vomiting Ex: ipecac