Week 2.2 - Gastric Acid Secretion

Question 1

What are the 2 mechanisms stimulating gastric acid secretion?

Answer 1

cephalic phase and gastric phase

Question 2

What occurs in the stimulatory cephalic phase?

Answer 2

think about/smell/taste food causes saliva and gastric acid secretion - vagus nerve releases ACh, causing release if ECL cells which release histamine

Question 3

What is the order of the parasympathetic response of food to hydrogen release?

Answer 3

ACH - ECL cells - Histamine - adenyl cyclase ATP to cAMP - PKA

Question 4

What occurs in the stimulatory gastric phase? (3)

Answer 4

• food in stomach causes distension. vagal and enteric nerves activated, releasing ACh.
• peptides in lumen activate g cells in antrum to release gastrin
• ACh and gastrin activate ECL cells releasing histamines

Question 5

What are the mechanisms inhibiting gastric acid secretion?

Answer 5

cephalic phase, gastric phase and intestinal phase

Question 6

What occurs in the inhibitory cephalic phase?

Answer 6

stop thinking about/smelling food, vagal activity decreases

Question 7

What occurs in the inhibitory gastric phase?

Answer 7

high HCl causes low pH - negative feedback - inhibits gastrin secretion

Question 8

What occurs in the inhibitory intestinal phase?

Answer 8

• food moves into small intestine, acid gets into duodenum.
• duodenum should be neutral, acid triggers enterogastric effect.
• duodenum mucosa secretes secretin - enters blood and triggers release of bicarbonate, as well as decreasing gastrin activity.

Question 9

What influence on gastric release do fats and carbs in the duodenum have?

Answer 9

fats and carbs in duodenum induces release of GIP - gastric inhibitory peptide, inhibiting gastrin release

Question 10

Why is the cephalic phase important?

Answer 10

sterilising food before it enters stomach

Question 11

What are enterogastrones?

Answer 11

hormones released from glands in duodenal mucosa which inhibit gastric acid secretion and reduce gastric emptying rate

Question 12

What are some examples of enterogastrones?

Answer 12

secretin, GIP, CCK (cholecystokinin)

Question 13

How do enterogastrones reduce gastric emptying rate?

Answer 13

contract the pyloric sphyncter

Question 14

What do chief cells secrete?

Answer 14

pepsinogen

Question 15

What is pepsinogen and why is it present?

Answer 15

inactive form of pepsin. pepsin denatures proteins so cant be exposed to cells directly

Question 16

When does pepsinogen convert to pepsin?

Answer 16

when pH is below 3. when above 3 it converts back to pepsinogen

Question 17

How is the small intestine protected from pepsin?

Answer 17

the small intestine is neutral in pH, and pepsin denatures at neutral pH.

Question 18

What are the mechanisms for control of pepsin release?

Answer 18

same as gastric acid release - gastrin, ACh and histamines trigger it and prostaglandins inhibit it

Question 19

How is gastric mucus produced and what’s its purpose?

Answer 19

• by mucous neck cells and surface epithelial cells.
• for lubrication and protect stomach wall from action of HCl
• has neutral pH so protects against pepsin digestion of stomach wall