2 Gastric Secretions

Question 1

How much gastric juice is secreted per day and where does the gastric juice arise from?

Answer 1

2 litres Arises from gastric mucosa

Question 2

Where are muscosal gland cells found

Answer 2

Gastric pits

Question 3

what are the two regions of gastric mucosa?

Answer 3

oxyntic mucosa: fundus and body

pyloric gland area: in antrum

Question 4

Answer 4

Question 5

What is secreted by: Mucous neck cells Surface epithelial cells Parietal cells Chief cells

Answer 5

Mucous Mucous HCl and intrinsic factor Pepsinogen

Question 6

Discuss how HCl is produced by parietal cells

Answer 6

Cl- is transported from plasma to parietal cells via anti- transport protein, which also transports HCO3- into plasma

Cl- transported from parietal cell into gastric lumen via co transporter protein, along with k+

H+ transported into gastric lumen via proton pump in exchange for K+

Net effect:

movement of H+ into lumen

movement of Cl- into lumen

recycling of K+

Question 7

How does HCl aid digestion?

Answer 7

1. Activating enzyme pepsin and providing acid medium for optimal pepsin activity 2. Aids breakdown of connective tissue and muscle fibres

Question 8

What is significant about the acid environment produced by Hcl

Answer 8

Non specific defence mechanism, kills ingested micro organisms

Question 9

What is intrinsic factor

Answer 9

Released by parietal cells Binds to vitamin B12 and allows absorption in ileum

Question 10

What is the major digestive constituent of gastric secretion?

Answer 10

Pepsinogen- produced by chief cells

Question 11

What are the phases of gastric secretion?

Answer 11

Cephalic phase Gastric phase Intestinal phase

Question 12

What is the cephalic phase? What is it stimulated by? What is the proportion of gastric secretion through this phase? What does its activity depend on?

Answer 12

When gastric secretion is stimulated prior to arrival of food in stomach Stimulated by thought, expectation, sight, taste, chewing and swallowing of food Contributes 40% of gastric secretion Depends on activity of vagus nerve

Question 13

Parasympathetic control of HCl secretion

Answer 13

Question 14

What is the gastric phase? Why does it occur?

Answer 14

When food reaches stomach and there is gastric secretion (50-60%) 1. Local vago vagal reflexes in response to mechanical stimulation due to presence of food in antrum (not involving CNS) 2. Stimulation of gastrin release from G cells by peptide fragments of partially digested proteins (major mechanism)

Question 15

Why does the intestinal phase occur? How much does it account for

Answer 15

5% of gastric secretions Due to circulating amino acids on parietal cells, or gastrin produced in dudodenal endocrine cells

Question 16

Gastric circulation: Share of CO? Mechanisms?

Answer 16

Resting is 0.5%, active is >10% Local metabolite production (Pg maintain capillary network) Release of vasoactive intestinal polypeptide (VIP) from local nerves causing vasodilatation

Question 17

Inhibition of gastric secretion (4)

Answer 17

As a meal gradually passes small intestine, secretions are reduced:

1. Removal of peptide fragments (not present to stimulate gastrin release)
2. Removal of food-> decrease pH, at pH less than 2, gastrin release from G cells inhibited directly and via somatostatin release
3. Distention of duodenum-> enterogastrone (mix of hormones CCK) from duodenal wall-> inhibits gastrin release (G cells or SS)
4. Influenced by cephalic factors like fear or depression

Question 18

Protection of gastric mucosa mechanisms (4)

Answer 18

Prevent self digestion

1. Luminal membranes of gastric mucosal cells impermeable to H+. Cells are interconnected with tight junctions, no H+ movement between cells
2. Negative feedback pH<2 inhibits G cells directly and via SS release from D cells
3. Mucous released from surface epithelial cells
4. Rapid repair of damaged mucosa (cells lining stomach turnover- 3 days), local pG production- nourishment by causing local vasodilatation and stimulate local bicarbonate production