Control 3

Question 1

Where are gut hormones secreted from?

Answer 1

Enteroendocrine cells of the alimentary canal

Question 2

What are enteroendocrine cells?

Answer 2

A large family of cells that are specialised for their own stimuli and secretions

Question 3

What is the structure of an enteroendocrine cell?

Answer 3

Small apical membrane with lots of sensory apparatus

Broad basolateral surface close to blood vessels

Question 4

What happens in the apical membrane of an enteroendocrine cell

Answer 4

it has lots of sensory apparatus so - receptors and intracellular signalling techniques that can sense changes in the gut contents or activation by neurotransmitters

Question 5

What happens in the basolateral membrane of an enteroendocrine cell

Answer 5

For rapid distribution, and near basolateral membrane there are vesicles with their secretatory products ready for exocytosis

Question 6

What organs do most gut hormones regulate?

Answer 6

Nearby gut organs,

although for hormones to get there they need to travel a long way via liver, heart and lungs

Question 7

What organs are the ones that mainly secrete hormones?

Answer 7

Stomach, small intestine and pancreas

Question 8

What do D cells in the stomach do?

Answer 8

secrete the gut hormone somatostatin, which inhibits the secretion of acid from parietal cells in the gastric pits.

Question 9

What do enterochrommaffin like cells ECl in gastric mucosa do?

Answer 9

Secrete histamine. Which binds to H2 receptors on the parietal cells, stimulating acid secretion.

Question 10

What are the particular functions controlled by enteroendocrine cells

Answer 10

GLUCOSE REGULATION (e.g. insulin & glucagon)
APPETITE REGULATION (e.g. ghrelin & peptide YY)
GUT FUNCTION REGULATION (e.g. somatostatin, secretin, cholecystokinin, gastrin and glucose-dependent insulinotropic peptide)

Question 11

Where is gastrin synthesised?

Answer 11

G-cells in the distal end of the stomach (gastric antrum), the proximal duodenum, and to a lesser extent the pancreas.

Question 12

How is the secretion of gastrin stimulated?

Answer 12

presence of single amino acids and small peptides in the stomach (remember that the stomach is the first site of protein digestion). Also, mechanoreceptors in the stomach wall that detect the presence of a meal (inferred by stretching) stimulate gastrin secretion. Lastly, the parasympathetic nervous system can stimulate gastrin release by releasing gastrin-releasing peptide from vagal efferents.

Question 13

What does gastrin do?

Answer 13

causes an increase in gastric acid secretion from parietal cells in the stomach.

Question 14

What is the negative feedback loop of gastrin secretion? What’s it for?

Answer 14

if the pH of chyme in the duodenum drops below 3 (pH<3), secretion will be reduced. This is to protect the duodenal mucosa.

Question 15

Where is Secretin synthesised?

Answer 15

S-cells in the proximal small intestine (duodenum and the jejunum).

Question 16

What stimulates secretin synthesis?

Answer 16

a drop in pH in the duodenal lumen (usually following acid chyme leaving the stomach through the pyloric sphincter).

Question 17

what does secretin do?

Answer 17

stimulates the secretion of bicarbonate rich juice from the exocrine pancreas (to neutralise the acid).

Question 18

What does excessive levels of secretin do?

Answer 18

inhibit the secretion of acid by the stomach and inhibit gastric emptying (to prevent further exacerbation of the acidic environment in the small intestine, as this will be causing mucosal damage).

Question 19

Where is somatostasin synthesised?

Answer 19

D (delta) cells in stomach, pancreas and small intestine in response

Question 20

What stimulates somatostatin secretion?

Answer 20

in response to a mixed meal

Increased [H+] or decrease pH

Question 21

What does somatostatin do?

Answer 21

a number of inhibitory effects. It decreases secretion of gastric acid via two mechanisms. It inhibits G-cells form secreting gastrin (which promotes acid secretion), and it inhibits ECL cells from secreting histamine. It also decreases motility of the gut and decreases gastric emptying.

Question 22

What is somatostatin described as? Why?

Answer 22

Universal inhibitor because it has an enormous number of inhibitory functions by vagus nerve

Question 23

Where is cholecystokinin secreted?

Answer 23

I-cells in the small intestine

Question 24

What stimulates cholecystokinin secretion?

Answer 24

Fats and peptide ie a mixed meal in lumen

Question 25

What effects does cholecystokinin have?

Answer 25

increased secretion of pancreatic enzymes
reduced gastric emptying
gall bladder contraction
reduced appetite

Question 26

What is special about cholecystokinin?

Answer 26

able to be secreted and triggers these effects without any input from the autonomic nervous system (act independent of vagus nerve)

Question 27

What is the Glucose-dependent insuliotropic peptide also called? (GIP)

Answer 27

Gastric inhibitory peptide​

Question 28

Where is GIP secreted?

Answer 28

K cells in the duodenum and jejunum

Question 29

What does GIP do?

Answer 29

involved with glucose storage, with its main physiological effect being the upregulation of insulin secretion in response to glucose concentration in the small intestine

Question 30

What does GIP in high conc do?

Answer 30

have inhibitory effects on stomach function