DRS - stomach

Question 1

Parts of the stomach (from top to bottom)

Answer 1

Fundus
Corpus
Antrum
Pylorus

Question 2

Functions of the stomach

Answer 2

Stores food
Mixes food with secretions
Regulated release of food into the duodenum
Secretes gastric juices

Question 3

Where are mucous neck cells found and what are their function?

Answer 3

Found in the stomach

They secrete mucous and bicarbonate, the mucous traps the bicarbonate and the bicarbonate neutralises acid

Question 4

Where are parietal cells found and what do they secrete?

Answer 4

Found in the corpus of the stomach

Secrete acid and intrinsic factors (IFs)

Question 5

Where are EC cells found and what is their function?

Answer 5

Found in the corpus in the stomach and secrete histamine as a trigger for acid secretion

Question 6

Where are chief cells found and what is their function?

Answer 6

Found in the corpus of the stomach and they secrete pepsinogen and lipase for fat digestion

Question 7

Where are D cells found and what is their function?

Answer 7

D cells are found in the base of the stomach and some in the corpus. They secrete somatostatin which is a major inhibitor of acid secretion.

Question 8

Where are G cells found and what is their function?

Answer 8

G cells are found in the base of the stomach. They secrete gastrin as a trigger of acid secretion.

Question 9

The mechanism of gastric acid secretion

Answer 9

• carbon dioxide and water combine to form H+ and HCO3- (by carbonic anhydrase)
• The HCO3- leaves cell via HCO3-Cl- exchanger (requires ATP) on basolateral membrane, Cl- enters cell
• The H+ leaves the cell via a H+K+ exchanger (requires ATP) on the apical membrane, K+ enters cell
• Cl- and K+ entering the cell leave the cell via channels on the apical membrane, down concentration gradients

Question 10

What is the alkaline tide?

Answer 10

When the HCO3- exits the parietal cell which increases the alkalinity

Question 11

What are the 3 triggers for acid secretion?

Answer 11

histamine
acetylcholine
gastrin

Question 12

How does histamine regulate acid secretion?

Answer 12

Acts via a PKA pathway:

• histamine binds to a H2 receptor which is associated with a Gs protein
• alpha subunit activates adenylyl cyclase
• ATP converted to cAMP which activates PKA
• PKA phosphorylates and increases the activity of the HK pump

Question 13

How does ACh regulate acid secretion?

Answer 13

• The presence of food in the stomach causes distension of the stomach
• This causes release of ACh by the vagus nerve
• ACh binds to an M3 muscarinic receptor on the parietal cell which is associated with a Gq protein
• The alpha subunit activates phospholipase C which produces IP3 and DAG
• IP3 binds to the IP3 receptor on the ER to increase calcium release. Increased calcium increases the activity of the HK pump
• DAG activates the PKC pathway which phosphorylates the HK pump increasing its activity

Question 14

How does gastrin regulate acid secretion?

Answer 14

• Gastrin binds to the CCK receptor which is associated with a Gq protein
• phospholipase C –> IP3 and DAG
• IP3 –> ER –> increase calcium –> increase HK activity
• DAG –> PKC –> phosphorylation of HK pump to increase activity

Question 15

How does somatostatin work?

Answer 15

Produced by D cells
Inhibits histamine mediated acid production
Binds to a GPCR which inhibits adenylyl cyclase

Question 16

How is somatostatin inhibited?

Answer 16

Stimulation of the vagus nerve (by distension of the stomach due to presence of food) and subsequent release of ACh suppresses D cells from releasing somatostatin

Question 17

Where are paracrine D cells found and what are they stimulated by?

Answer 17

In the corpus of the stomach

triggered by hormonal and neuronal mechanisms

Question 18

Where are endocrine D cells found and what are they stimulated by?

Answer 18

In the antrum of the stomach

Triggered by a low intra-luminal pH

Question 19

What stimulates G cells to make gastrin?

Answer 19

Gastrin releasing peptide

Question 20

Name 5 inhibitors of acid secretion

Answer 20

somatostatin
VIP 
CCK - produced by I cells
Prostaglandins
Secretin - released by duodenal S cells

Question 21

Name 2 pharmacological inhibitors of acid secretion

Answer 21

Proton pump inhibitors - omeprazole

H2 receptor antagonists - cimetidine

Question 22

What are the 4 phases of gastric acid secretion?

Answer 22

1. Basal phase - circadian rhythm, low am, high pm
2. Cephalic phase - sight, smell, thought of food
3. Gastric phase - food in stomach detected
4. Intestinal phase - partially digested food in duodenum stimulates duodenal G cells to produce gastrin

Question 23

What are prostaglandins for in the stomach?

Answer 23

Maintain the mucosal diffusion barrier by inhibiting acid secretion, stimulating acid secretion and mucous secretion

Question 24

What is helicobacter pylori and what can it cause?

Answer 24

Gram negative microaerophilic bacterium

Can cause gastritis, gastric and duodenal ulcers and gastric cancer

Question 25

What does helicobacteri pylori infection in the antrum cause?

Answer 25

G cells to hypersecrete gastrin

decrease in antral D cell somatostatin release

Question 26

What are intrinsic factors important for? What can their loss lead to?

Answer 26

Important for binding of vitamin B12 and absorption of B12 in the terminal ileum
Loss of this can lead to pernicious anaemia which can lead to megaloblastic anaemia where parietal cells are destroyed