GI System

Question 1

Mucosa layer of GI

Answer 1

Mucosa: inner layer facing the lumen

Mucosal epithelium: contain epithelial, endocrine, exocrine and stem cells

Lamina propria: nerve fibers, small blood and lymph vessels, peyer’s patches (GALT)

Muscularis mucosae: thin layer of smooth muscle (moves villi to alter surface area)
- innervated by submucosal plexus of ENS

Question 2

Submucosa layer of GI tract

Answer 2

Submucosa: middle layer

Connective tissue: larger blood and lymph vessels

Submucosal plexus of ENS: 1st major nerve network of ENS, innervates muscularis mucosae and mucosal epithelium

Question 3

Muscularis Externa and

Serosa layers of GI tract

Answer 3

Muscularis externa: outer layer (2 layers of smooth muscle)

Inner circular layer: decreases diameter of lumen

Outer longitudinal layer: shortens tube

Myenteric plexus of ENS: 2nd major nerve network of ENS, innervates motor activity of muscularis externa

Serosa: connective tissue membrane continuous with peritoneum, forms sheets of mesentery to hold intestines in place.

Question 4

Pacemaker cells of the GI

Answer 4

slow-wave potentials in the interstitial cells of Cajal

Controls tempo of single-unit smooth muscle contraction

Question 5

Similarities between ENS and CNS

Answer 5

Similarities with CNS include:

Contains intrinsic neurons (function within the confine of their own structure)

NT secretions identical to those found in the CNS

Glial support cells

Diffusion barrier similar to BBB such that capillaries surrounding ganglia are not permeable.

Has an integrating centre, like the one in the CNS

Question 6

G cells

Answer 6

Gastrin (G cells): in the stomach, stimulated by peptides/AA

Targets ECL and parietal cells

Stimulates gastric acid secretion and mucosal growth.

Gastrin family

Question 7

CCK

Answer 7

Cholecystokinin (CCK): in SI, stimulated by FA and some AA

Target gallbladder, pancreas and stomach

Stimulates gallbladder contraction, pancreatic enzyme secretion and inhibits gastric emptying and acid secretion.

Promotes satiety

Gastrin family

Question 8

GIP

Answer 8

Gastric inhibitory peptide (GIP): in SI, stimulated by glucose, FA and AA

Targets pancreatic beta cells, stimulates insulin release (feedforward mechanism), inhibits gastric emptying and acid secretion

Secretin family

Question 9

3 salivary glands

Answer 9

Parotid glands: produce watery solution of enzymes

Sublingual glands: produce mucus-rich saliva

Submandibular glands: mixed

Question 10

3 purposes of the gastric phase

Answer 10

storage (fundus), digestion (antrum) and defense (pH)

Question 11

4 purposes of the intestinal phase

Answer 11

Motility, surface area maximization, absorption, secretions

Question 12

Isotonic NaCl secretion in SI/colon

Answer 12

Cl- enters cell via NKCC (basolateral Na, K, Cl- cotransport)
Cl- enters lumen via CFTR (apical)
Na+ back to ECM by Na-K ATPase
Na+ and water follows Cl- charge via paracellular pathway –> isotonic solution

Question 13

Gastric cells and their secretions (3) and paracrine molecules (3)

Answer 13

G-cells: secrete gastrin hormone in blood to promote HCl secretion.

Parietal cells: secrete HCl (activates pepsin, triggers SS release, denature proteins, kills pathogens, inactivate salivary amylase)

Chief cells: secrete pepsinogen (activated to pepsin) and gastric lipase

Paracrine secretions:
ECL cells secrete histamine: stimulates acid secretion

Parietal cells secrete IF: complexes with vitamin B12 to help with its later absorption in SI.

D cells secrete somatostatin (SS): negative feedback for gastric phase secretion.