Gastric Secretion

Question 1

What are the 3 parts of the stomach?

Answer 1

Fundus
Body
Antrum

Question 2

What is the function of the fundus?

Answer 2

Storage

Question 3

What is the function of the body of the stomach?

Answer 3

Storage
Mucus, HCl, Pepsinogen and intrinsic factor production

Question 4

What is the function of the antrum of the stomach?

Answer 4

Mixing/ Grinding
Gastrin production

Question 5

What does mucous neck cells secrete?

Answer 5

Mucus

Question 6

What does chief cells secrete?

Answer 6

Pepsinogens - inactive precursor of pepsin

Question 7

What does parietal cells secrete?

Answer 7

HCl and Intrinsic factor

Question 8

What are the 3 main gastric glands?

Answer 8

Mucous neck cells
Chief cells
Parietal cells

Question 9

Explain how HCl is produced and released out apical membrane into stomach lumen

Answer 9

CO2 from blood crosses basolateral membrane of cell - joins with water and carbonic anhydrase to make carbonic acid
This dissociates into H and bicarbonate
H uses HKATPase pump
H and Cl join with water to make HCl

Question 10

What happens to bicarbonate when dissociated from carbonic acid?

Answer 10

Exchanges with Cl across basolateral membrane and leaves into blood to increase pH

Question 11

What can stimulate the HKATPase pump ?

Answer 11

Gastrin (hormone) binding on basolateral membrane to release Ca - protein kinase C
Histamine binds to release Gs then AC to convert ATP to cAMP which releases protein kinase A
ACh binds to muscarinic receptor releasing Ca - protein kinase C

Question 12

What can inhibit the HKATPase pump?

Answer 12

Prostaglandins

Question 13

What 3 mechanisms control gastric acid secretion?

Answer 13

Neurocrine - vagus/ local reflexes
Endocrine - gastrin
Paracrine - histamine

Question 14

Explain the cephalic phase - stimulating gastric acid secretion

Answer 14

Sight, smell and taste of food causes vagus nerve to release ACh and G cells to release gastrin - works on parietal cells
Gastrin/ACh works on ECL cells releasing histamine - parietal cells

Question 15

What during the gastric phase stimulates gastric acid secretion?

Answer 15

Distention of stomach
Peptides in lumen
Gastrin/ ACh

Question 16

How does distention of stomach stimulate gastric acid secretion?

Answer 16

Triggers vagal/ enteric reflexes releasing ACh which stimulates parietal cells

Question 17

How does peptides in stomach stimulate gastric acid secretion?

Answer 17

Triggers G cells which release gastrin - stimulates parietal cells

Question 18

How does gastrin/ ACh stimulate gastric acid secretion?

Answer 18

Triggers ECL cells to release histamine which stimulates parietal cells

Question 19

What in the cephalic phase inhibits secretion of gastric acid?

Answer 19

Stopping eating decreases vagal activity

Question 20

What in the gastric phase inhibits gastric acid secretion?

Answer 20

Decreased pH from increased HCl production then decreases gastrin

Question 21

What in the intestinal phase inhibits gastric acid secretion?

Answer 21

Acid in the duodenum
Fat/ CHO in the duodenum

Question 22

How does acid in the duodenum stop gastric acid secretion?

Answer 22

Enterogastric reflex and secretin release
These decrease gastric secretion and gastrin stimulation of parietal cells

Question 23

How does fat and CHO in the duodenum stop gastric acid secretion?

Answer 23

Causes GIP release which decreases gastrin secretion and parietal HCl secretion

Question 24

What are enterogastrones?

Answer 24

Hormones released from gland cells in the duodenal mucosa - secretin, CCK and GIP

Question 25

Why are enterogastrones released?

Answer 25

In response to acid , hypertonic solutions, fatty acids or monoglycerides in duodenum

Question 26

What is the function of enterogastrones?

Answer 26

Act collectively to prevent further acid build up in the duodenum

Question 27

What are the 2 strategies that enterogastrones use to prevent build up of acid in duodenum?

Answer 27

Inhibit gastric acid secretion Reduce gastric emptying so inhibit motility/ contract pyloric sphincter

Question 28

When is pepsin active?

Answer 28

In low pH <3

Question 29

What does zymogen storage prevent?

Answer 29

Zymogen is inactive precursor and prevents cellular digestion

Question 30

When is pepsins inactivated?

Answer 30

Neutral pH

Question 31

Where is gastric mucus produced?

Answer 31

By surface epithelial cells and mucus neck cells

Question 32

Explain the cytoprotective role of gastric mucus

Answer 32

Protects mucosal surface from mechanical injury Neutral pH from bicarbonate protects against gastric acid corrosion and pepsin digestion

Question 33

What is required for vitamin B12 absorption?

Answer 33

Intrinsic factor

Question 34

What is the only non-compensated/ essential function of the stomach?

Answer 34

Production of intrinsic factor

Question 35

Where is intrinsic factor/B12 complex absorbed?

Answer 35

From ileum

Question 36

What is the defect if low production of intrinsic factor?

Answer 36

Pernicious anaemia - failure of erythrocyte maturation