Session 4 - The Stomach

Question 1

Give some functions of the stomach

Answer 1

• Stores food
• Disinfects food
• Breaks down food into chyme (chemically and physically)

Question 2

What is the major role of parietal cells in the stomach?

Answer 2

Secrete stomach acid

Question 3

Which organelle of the parietal cells is responsible for production of Hydrogen ions?

Answer 3

Mitochondria

Question 4

How is stomach acid formed?

Answer 4

• Mitochondria split water into Hydroxide ions and Protons
• These protons are then pumped into the lumen of the stomach where they combine with chloride ions to form HCl
• The hydroxide ions from water combine with CO2 to form Hydrogen Carbonate

Question 5

How does Histamine cause the production of acid in the stomach?

Answer 5

• released from mast cells
• diffuse locally to bind to H2 receptors of parietal cells
• Second messenger cAMP then stimulated
• this causes protons to be pumped into the stomach

Question 6

How does the sight and smell of food stimulate acid production?

Answer 6

• activates parasympathetic nerves
• causes the release of Ach
• This then stimulates parietal cells directly + via Histamine

Question 7

How does the food arriving in the stomach stimulate the gastric pathway?

Answer 7

• food buffers acidic solution
• Increase in pH disinhibits gastrin
• Gastrin then causes more acid to be produced

Question 8

Which drug can be used to antagonise the action of Histamine?

Answer 8

Cimetidine

Question 9

Which drug is the most common PPI?

Answer 9

Omeprazole

Question 10

How is stomach mucus important in preventing damage to the stomach epithelium?

Answer 10

• mucus forms an unstirred layer that ions cannot pass through quickly
• Hydrogen Carbonate secreted by cells stays close to cell surface
• Hence pH at cell remains high

Question 11

How does alcohol damage stomach defences?

Answer 11

Dissolves mucus allowing acid to attack the stomach

Question 12

How do NSAIDS cause damage to the stomach epithelium?

Answer 12

• inhibit prostaglandins, which stimulate mucus secretion

- Less mucus secretion = easier for acid to penetrate

Question 13

How does receptive relaxation prevent reflux?

Answer 13

• as food travels down oesophagus, a neural reflex by the vagus nerve stimulates relaxation of stomach wall
• hence pressure doesn’t rise too much
• this limits reflux

Question 14

How is it ensured that chyme is only delivered to the stomach in small amounts?

Answer 14

As chyme reaches pyloric region of stomach, a small amount is ejected before a peristaltic wave of muscle contractions drives and close off the pyloric sphincter. The rest of the chyme now returns to the stomach and the cycle repeats