Lecture 23: Gastrointestinal 1

Question 1

Describe the cephalic and oral phases of the GI response

Answer 1

Cephalic phase and oral phase are very similar. Cephalic precedes oral, arises from thoughts about food/smelling/hearing about food. Leads to saliva secretion, gastric secretion, pancreatic secretions. Oral phase has mechanical and chemical digestion

Question 2

Describe how saliva is formed and modified, describe the swallowing reflex

Answer 2

Saliva is formed by the acinar cells and modulated by ductular cells, goes through nerve 9. Gets secreted by, NaCl is reabsorbed in exchange for HCO3 and K. This turns a isotonic solution to be hypotonic, alkaline.

Swallowing reflex: voluntary - tongue thrust up and back. Involuntary: nasopharynx closes, larynx elevates, upper esophageal sphincter relaxes, pharynx contracts. Peristalsis occurs

Question 3

Describe the anatomy of the somach

Answer 3

has three sections: cardia & lower esophageal sphincter (release of HCO3 and mucus), fundus and body (release of tons of stuff), antrum and pylorus (release of HCO3 and mucus)
stomach composed of gastric pits.

Question 4

Describe how gastric secretions are regulated

Answer 4

Regulated hormonally (endocrine), neurally, paracrine.
Distension of stomach leads to signals through vagal nerve to dorsal vagal centre. goes back down and causes release of Ach into enteric nervous system. This causes Ach onto enterochromaffin like cells to release histamine. this acts in paracrine manner on parietal cells. Ach released onto parietal cells, which release HCl. ENS releases gastrin release peptide onto G cells, this releases gastrin into the circulation to go to the stomach and act on parietal cells as well.

H+ in antrum goes to D cells, cause release of somatostatin to inhibit G cells.

Question 5

Describe how gastric motility is regulated and contributes to mechanical digestion in the stomach

Answer 5

Enteric nervous system myenteric plexus (submucosal plexus regulates secretion) innervates smooth muscle, is regulated by interstitial cells of Cajal which provide slow waves of depolarization to the muscle. Wave of contraction goes down stomach, food hits pyloric sphincter and bounces through contracted neck. this causes shearing/grinding of food

Question 6

What are the functions of saliva

Answer 6

lubricate and soften food
initiate digestion of carbohydrates
clean oral cavity (wash with lysozymes)
solubilize food molecules for taste

Question 7

How is HCl released?

Answer 7

large concentration gradient against HCl, lots of mitochondria. therefore lots of Co2 produced. carbonic anhydrase produces HCO3- and H+. HCO3- exchanged for Cl which goes through leak channel into stomach. H+ goes via a K/H pump.
tubulovesicular membrane increases number of K/H pumps