Lecture 3: Control of the gut- Hormones

Question 1

What are the three types of hormones in the GI tract?

Answer 1

Peptide Hormones (made of chains of AA’s)

• paracrine
• endocrine
• neurocrine

Question 2

What is an endocrine hormone?

Answer 2

Hormones that are released and travel to their effector organ via the bloodstream

Question 3

Where does everything drain into from the GI tract?

Answer 3

Portal circulation- venous, which goes through the liver, then into the heart via venous system and then pumped from the heart to where it needs to be.

Question 4

What is paracrine hormones?

Answer 4

Act locally, they diffuse

Question 5

What are neurocrine hormones?

Answer 5

Hormones released from the post-ganglionic fibres from neurones

Question 6

Give some examples of endocrine hormones in the gut:

Answer 6

• gastrin
• cholecystokinin
• secretin

Question 7

Give some examples of paracrine hormones in the gut:

Answer 7

-somatostatin

Question 8

Give some examples of neurocrine hormones in the gut:

Answer 8

-gastrin releasing peptide (GRP)

Question 9

Whar cells are all paracrine and endocrine hormones released from?

Answer 9

Enteroendocrine cells, which are scattered between the epithelial cells in the mucosa of the gut. They are found all the way between the stomach and the colon. They release hormones in response to food being taken into the GI tract/ in relation to stretch

Question 10

What are the 2 main families of hormones that control the GI tract?

Answer 10

• gastrin family (gastrin/cholecystokinin)

- secretin family (secretin/gastric inhibitory polypeptide)

Question 11

What is the function of gastrin?

Answer 11

-released from G cells in the stomach
-the gastrin released then goes on to cause parietal cells to release gastric acid (i.e. HCL) into the stomach
(regulate stomach acid)

Question 12

What are G cells stimulated by?

Answer 12

• breakdown of proteins in the stomach (small peptides/AA’s detected)
• directly by the vagus nerve
• stretch receptors in the stomach

Question 13

What is the function of cholecystokinin?

Answer 13

• when released it contracts the gall bladder, which sends bile into the duodenum
• stimulates the pancreas to release digestive enzymes
• relaxes the sphincter of oddi

Question 14

Where do bile and digestive enzymes enter the duodenum?

Answer 14

Through a sphincter (when relaxed) called the sphincter of oddi

Question 15

From what cells is cholecystokinin released from?

Answer 15

-released from I cells in the duodenum and jejunum in response to protein products/fat breakdown products e.g.monoglycerides/detection of acid

Question 16

From what cells is secretin released from?

Answer 16

S cells in the duodenum, which are stimulated when the acidic chyme enters the duodenum

Question 17

What is the function of secretin?

Answer 17

-stimulates bicarbonate rich secretions from the biliary system/pancreas to neutralise the acidic chyme

Question 18

What is the biliary system?

Answer 18

Liver, gall bladder, and bile ducts

Question 19

When is gastric inhibitory polypeptide released?

Answer 19

Stimulated by all the main food groups

Question 20

What is the function of gastric inhibitory polypeptide?

Answer 20

• reduces gasctric acid secretion

- increases insulin secretion

Question 21

What is the function of somatostatin?

Answer 21

Switches off the G cells producing gastrin

Question 22

What is somatostatin stimulated by?

Answer 22

When it detects a low pH

Question 23

What cells secrete somatostatin?

Answer 23

D cells in the stomach

Question 24

What is the function of gastrin releasing peptide?

Answer 24

Released from post-ganglionic fibres and stimulates G cells to produce gastrin and therefore parietal cells to produce stomach acid