Gastric Secretions

Question 1

Which cells in the stomach secrete mucous?

Answer 1

Gastric mucosal cells

Question 2

Name the two types of gastric mucosa, where they are found, and what they secrete.

Answer 2

. Oxyntic mucosa in fundus and body (secrete HCl + intrinsic factor)
. Pyloric glands in pyloric antrum (secrete gastrin)

Question 3

Which type of cells release intrinsic factor? What is intrinsic factor?

Answer 3

Secreted by parietal cells, IF binds to vitamin B12 to enable its absorption

Question 4

What is gastrin?

Answer 4

Hormone that stimulates secretion of HCl

Question 5

What is gastric acid composed of?

Answer 5

Hydrochloric acid

Question 6

What are gastric pits?

Answer 6

Dips in the lining of the stomach where tubular gastric glands sit with parietal and chief cells

Question 7

What do parietal cells do? Give an example of a parietal cell.

Answer 7

. Secrete HCl and intrinsic factor

. E.g. oxyntic cells

Question 8

How does hydrochloric acid aid digestion?

Answer 8

. Activates pepsin and gives optimum pH for pepsin to function
. Helps break down connective tissue and muscle fibres

Question 9

Which cells produce pepsinogen?

Answer 9

Chief cells

Question 10

Give the main components of gastric secretion

Answer 10

Pepsinogen (precursor of pepsin), HCl, intrinsic factor

Question 11

What is the cephalic phase of gastric secretion?

Answer 11

Gastric secretion stimulated prior to the arrival of food in the stomach (by sight, smell, taste, chewing, swallowing)

Question 12

Which nerve stimulates the cephalic phase of gastric secretion?

Answer 12

Vagus nerve (CNX)

Question 13

What happens to the intensity of gastric secretion when food reaches the stomach?

Answer 13

Increases

Question 14

Describe the mechanism by which gastric secretion increases when food reaches the stomach.

Answer 14

. Food entering stomach antrum gives mechanical stimulation, activating local vago-vagal reflexes
. Fragments of partially digested peptides stimulate release of gastrin from G-cells

Question 15

Where are parietal cells and chief cells found?

Answer 15

In the gastric pits

Question 16

Why do people sometimes feel sleepy after a meal?

Answer 16

Blood flow is directed to the stomach for digestion of food, so there is decreased blood flow to the brain

Question 17

What happens to the level of gastric secretion when food moves into the small intestine?

Answer 17

Decreases

Question 18

Why do gastric secretions decrease when food moves into the small intestine? (Give 3 reason)

Answer 18

. Peptides no longer in stomach to stimulate release of gastrin
. Removal of food lowers pH. Below pH 2, somatostatin is activated to inhibit the release of gastrin from G-cells
. Enterogastrone (mixture of hormones including cholecystokinin) released, which inhibits release of gastrin, either directly or via somatostatin

Question 19

Give examples of when gastrin secretion can be influenced by cephalic factors

Answer 19

Gastric secretion can be reduced with fear or depression

Question 20

How are gastric mucosa protected from self-digestion? (Give 4 ways)

Answer 20

. Luminal membranes impermeable to H+, and tight junctions between mucosa means no paracellular transfer of H+
. Negative feedback mechanism- pH less than 2 inhibits G-cells from producing gastrin (directly or indirectly via somatostatin from D-cells)
. Gastric epithelia secrete protective mucous
. Cells lining stomach have turnover of 3 days, and damaged mucosa quickly repaired

Question 21

Which type of cell produces somatostatin?

Answer 21

D-cells (delta-cells)