Lecture 3 : Secretions of Stomach

Question 1

Stomach functions

Answer 1

• Secretion
• Peristalsis (motility)
• Digestion of carbs, proteins and fats
• Absorption

Question 2

Stomach diagram

Answer 2

Corpus contains mostly parietal cells and chief cells, but also contains ECL and D cells

Antrum and Pylorus contains no parietal cells.
Does contain G cells and D cells

Question 3

How do parietal cells secrete acid?

Answer 3

Question 4

How is acid secretion regulated?

Answer 4

Question 5

How is acid secretion and peristalsis inhibited?

Answer 5

Hormones called enterogastrones are secreted by duodenum.

Eg. Somatostatin, CCK, Prostaglandins, Secretin

Secretin is released by S cells in duodenum, stimulated by fat and acid in duodenum. Inhibits somatostatin release and AG release.

CCK produced by I cells in duodenum and jejenum in response to fat. Directly reduces parietal cell acid secretion.

Question 6

What are some pharmacological inhibitors of acid secretion?

Answer 6

Omeprazole :
- Proton pump inhibitor
- Directly impacts proton pump

Cimetidine and Ranitidine
- H2 receptor antagonists
- Competitve antagonists of histamine at parietal cell H2 receptors

Question 7

Phases of Gastric Secretion

Answer 7

Question 8

Pepsin as a gastric secretion

Answer 8

Initiates protein digestion.

Obtained from pepsinogen (from chief cells)

ACh is trigger for pepsinogen secretion from chief cells.

Happens at the same time as acid secretion because acids secretion is also triggered by ACh, and peptides trigger antral G-cell gastrin secretion too

Question 9

Mucus as a gastric secretion

Answer 9

Secreted by mucus cells

Contains trapped bicarbonates HCO3-

Mucus layer protects stomach lumen from acid

Prostaglandins maintain mucosal diffusion
barrier, by inhibiting acid secretion whilst also stimulating HCO3- secretion and mucus secretion

Question 10

Intrinsic factors as a gastric secretion

Answer 10

Question 11

What is a peptic ulcer

Answer 11

Leading cause is helicobacter plyori, which is an acid thriving bacteria colonising stomach of around 40% of people. Stimulates acid production and therefore barrier damage.

IN ANTRUM:
Causes G cells to hypersecrete gastrin, and decrease antral D-Cell somatostatin release, causing increase in acid concentration, causing hypergastrinaemia, which could lead to duodenal cancer.

IN CORPUS:
Reduces acid secretion leading to HYPOCHLORHYDRIA, leading to gastic ulcers. Low acid, less stomach bacteria killed
Helicobater Plyori produces urease:
Urea -> NH3 + CO2+ H2O -> NH4+ + HCO3- -> neutralizes stomach acid

Treatment consists of antibiotics and proton pump inhibitors