Gastric Secretion/Digestion

Question 1

4 phases of gastric acid secretion

Answer 1

Basal phase, cephalic phase, gastric phase, intestinal phase

Question 2

Basal (interdigestive) phase

Answer 2

• phase of gastric acid secretion following circadian rhythm
• most secretion in evening/least at night
• secretion of acid incresed with eating

Question 3

Cephalic phase

Answer 3

phase of gastric acid secretion mediated mainly by vagus

• vagus stimulation causes release of ACh, histamine release from ECL cells, release of gastrin-releasing peptide from vagal/enteric neurons, adn inhibition of somatostatin release from D cells
• 30% of acid secretion

Question 4

Gastric phase

Answer 4

phase of gastric acid secretion

• begins when food enters stomach
• activates vasovagal reflex and local ENS reflexes
• partially digested proteins stimulate gastrin release from G cells in antrum
• 50-60% of total acid secretion

Question 5

Intestinal phase

Answer 5

• last phase of gastric acid secretion
• about 5-10% of acid secretion
• presence of amino acid and partially digested peptides in proximal SI stimulates duodenal gastrin cells to release gastrin

Question 6

What molecules stimulate acid secretion

Answer 6

ACh, histamine, gastrin

also eating

Question 7

which phase of gastric acid secretion is most responsible for H secretion

Answer 7

gastric phase (50-60%) > cephalic phase (30%) 
-basal/inter-digestive phase and intestinal phases last

Question 8

transporters facilitating gastric acid secretion

Answer 8

Apical H/K ATPase pumping H out into lumen and K in

Basolateral Cl/HCO3 anion exchange – HCO3 transported down gradient out of cell allowing Cl to move up gradient into cell

Question 9

movement of Cl in parietal cells

Answer 9

Cl moves across basolateral membrane into cell due to secondary active transport (Cl/HCO3 anion exchange) then across apical side via passive transport

Question 10

movement of H into lumen from parietal cells

Answer 10

H created from carbonic anhydrase breakdown of CO2 and water – moves into lumen via H/K ATPase primary active transport pump against gradient

Question 11

movement of water through parietal cells

Answer 11

move transcellularly following H and Cl movement

Question 12

alkaline tide

Answer 12

H secretion into lumen plus HCO3 transport across basolateral side into blood leads to high pH of venous blood leaving stomach

Question 13

Parietal cell role

Answer 13

secrete acid and intrinsic factor

Question 14

role of intrinsic factor

Answer 14

secreted by parietal cells in stomach; required for vitamin B12 absorption

• only indispensable substance in gastric juice

Question 15

what provides protective layer of gastric surface

Answer 15

mucous and bicarbonate secretion

- this also helps prevent diffusional dissipation of enormous pH gradient

Question 16

role of mucous/bicarb secretion

Answer 16

protection and prevent diffusional dissipation of enormous pH gradient

Question 17

largest ion gradient in body

Answer 17

that of gastric lumen to blood (5.4 pH units aka 10^6 fold concentration gradient)