GI Hormones

Question 1

Outline the role of secretin.

Answer 1

1. Triggers the pancreas to release bicarbonate-rich fluid.
2. Reduces gastric acid secretion by inhibiting parietal cells in the stomach.
3. Promotes bicarbonate secretion in the liver.
4. Slows the transfer of chyme from the stomach to the duodenum, preventing overwhelming the intestine with acid.

Question 2

Outline secretin release.

Answer 2

Secreted by duodenal S cells in response to pH < 4.5 in the small intestine.

Question 3

Outline the role of gastrin.

Answer 3

1. Stomach: Stimulates gastric acid (HCl) secretion by parietal cells.
2. Increases motility and gastric contractions to help mix food and digestive enzymes.
3. Promotes the relaxation of the pyloric sphincter.

Question 4

Outline gastrin release.

Answer 4

Released when:
- Presence of amino acids in stomach
- Mechanical stretching of stomach wall
- Act from vagus nerve

Question 5

Outline the role of CCK.

Answer 5

1. Stimulates contraction of the gallbladder.
2. Stimulates the pancreas to release digestive enzymes (lipase, amylase, proteases).
3. Inhibits gastric emptying.

Question 6

Outline CCK release.

Answer 6

Released in response to the presence of fatty acids and amino acids in the duodenum.

Question 7

Outline the role of GIP.

Answer 7

1. Stimulates insulin release (incretin effect) to help regulate blood glucose after meals.
2. Inhibits gastric acid secretion and gastric motility to slow down digestion.

Question 8

Outline GIP release.

Answer 8

Released in response to carbohydrates and fats entering the small intestine.

Question 9

Outline the role of somatostatin.

Answer 9

1. Inhibits the release of gastrin, reducing gastric acid secretion.
2. Inhibits both insulin and glucagon secretion to regulate glucose metabolism.
3. Inhibits the secretion of several digestive enzymes and slows motility.

Question 10

Outline somatostatin release.

Answer 10

Released in response to low pH in the stomach.

Question 11

Outline the role of peptide YY.

Answer 11

1. Reduces gastric motility and delays gastric emptying, contributing to satiety.
2. Decreases intestinal motility and inhibits digestive enzyme secretion.
3. Signals the hypothalamus to suppress appetite and promote feelings of fullness.

Question 12

Outline peptide YY release.

Answer 12

Released after eating, particularly in response to the presence of fats and proteins in the small intestine.

Question 13

How does gastrin cause hcl secretion? (primarily)

Answer 13

Indirect Stimulation via Histamine Release:
- Stimulates ECL (enterochromaffin-like) cells in the stomach lining to release histamine.
- Histamine binds to H2 receptors on parietal cells, further enhancing HCl secretion.