Stomach Physiology

Question 0

What cells are present in gastric pits?

Answer 0

• Neck cells
• Parietal cells
• Chief cells
• G-cells

Question 1

What is the purpose of the stomach?

Answer 1

• Store food
• Disinfect food
• Breakdown food into chyme

Question 2

What do parietal cells do?

Answer 2

• Produce H+
• Proton pumps (in canaliculi) expel H+ against its conc gradient
• OH- reacts with CO2 and bicarbonate ions are secreted into the blood

Question 3

What stimulates parietal cells to produce acid?

Answer 3

• ACh
• Gastrin
• Histamine

Question 4

Tell me about ACh.

Answer 4

• Released from postganglionic parasympathetic neurones
• Acts on muscarinic receptors on parietal cells
• Release is stimulated by gastric distension

Question 5

What binds to muscarinic receptors on parietal cells?

Answer 5

ACh

Question 6

Tell me about Gastrin.

Answer 6

• Released from G cells
• Secretion is stimulated by presence of peptides and ACh from intrinsic neurones
• Secretion is inhibited by low gastric pH

Question 7

What is secreted by G cells?

Answer 7

Gastrin

Question 8

Gastric distension stimulates release of ___________.

Answer 8

ACh

Question 9

Tell me about Histamine.

Answer 9

• Released from mast cells
• Binds to H2 surface receptors on parietal cells
• Stimulates acid secretion via secondary messenger pathway (cAMP)
• Works as an amplifier as mast cells are stimulated by Gastrin and ACh

Question 10

What is released from mast cells?

Answer 10

Histamine

Question 11

What binds to H2 receptors?

Answer 11

Histamine

Question 12

Where are H2 receptors located?

Answer 12

Parietal cells

Question 13

What are the three phases of gastric secretion?

Answer 13

• Cephalic phase
• Gastric phase
• Intestinal phase

Question 14

What happens in the Cephalic phase?

Answer 14

• Sight and smell of food and swallowing activates the PNS
• ACh is released
• ACh act directly on parietal cells and via histamine to increase acid production

Question 15

Where can muscarinic receptors be found?

Answer 15

Parietal cells

Question 16

What happens in the gastric phase?

Answer 16

• Distension of the stomach further stimulates ACh release
• Food acts as a buffer, causing pH to rise
• Rise in pH dis-inhibits gastrin production
• Breakdown of proteins into peptides further stimulates gastrin release
• Increased acid production

Question 17

What happens in the intestinal phase?

Answer 17

• Chyme leaving the stomach stimulates the release of CCK and gastric inhibitory peptide
• They antagonise Gastrin
• No food to act as buffer, pH falls
• Low pH inhibits Gastrin, acid production decreases

Question 18

What inhibits acid secretion?

Answer 18

CCK

Gastric inhibitory peptide

Question 19

What do neck cells secrete?

Answer 19

Mucus

Question 20

Outline the stomachs defences

Answer 20

• Thick, sticky mucus is secreted by neck cells to protect gastric musoca
• Surface epithelial cells secrete HCO3-
• H+ ions react with amine groups on the mucus or HCO3- and become neutralised

Question 21

Describe the properties of the mucus.

Answer 21

• Thick, sticky and basic

- Forms an I stirred layer that ions cannot easily move through

Question 22

What stimulates mucus and HCO3- secretion?

Answer 22

Prostaglandins

Question 23

What inhibits production of prostaglandins?

Answer 23

NSAIDs