Control of gut hormones

Question 1

Outline how endocrine hormones travel around the body

Answer 1

• Peptides are released by endocrine cells
• They enter into portal circulation
• Then pass through the liver
• Enter systemic circulation
• End up pretty close to where they were released.

Question 2

Outline how paracrine hormones travel around the body

Answer 2

• Peptides are released from endocrine cells
• They act in their local environment
• They diffuse short distances to reach target cells

Question 3

Outline how neurocrine hormones are released

Answer 3

• Peptides are released by neurones in the GI tract
• They are only released after an action potential.

Question 4

What kind of cells release endocrine and paracrine hormones?

Answer 4

Enteroendocrine cells

Question 5

What stimulates enteroendocrine cells to release hormones?

Answer 5

• Food being taken into the GI tract e.g. through detection of peptides, amino acids, fatty acids, oral glucose etc.
• In relation to stretch

Question 6

Which 2 families of hormones control many of the functions of the GI tract?

Answer 6

• Gastrin family: gastrin, cholecystokinin
• Secretin family: secretin, GIP

Question 7

Give some key information about gastrin

Answer 7

• Endocrine
• Released by G cells in antrum of stomach
• Increases gastric acid secretion by parietal cells.
• Release is stimulated by breakdown of proteins in the stomach, vagus nerve, stretch receptors in stomach.

Question 8

Give some key information about cholecystokinin

Answer 8

• Endocrine
• Secreted by I cells in the duodenum and jejunum.
• Stimulated by fat and protein
• Causes gall bladder to contract and send bile into the duodenum.
• Stimulates pancreas to release digestive enzymes.
• Relaxes sphincter of Oddi, allowing bile and digestive enzymes to reach the duodenum at the same time.

Question 9

Give some key information about secretin

Answer 9

• Endocrine
• Released by S cells in the duodenum
• Low pH stimulates secretin release e.g. due to presence of H+ and fatty acids
• Increases release of HCO3 from pancreas/gall bladder to neutralise acidic chyme.
• Decreases gastric acid secretion

Question 10

Give some key information about Gastric inhibitory polypeptide (GIP)

Answer 10

• Endocrine
• Released by cells in the duodenum and jejunum
• Stimulated by sugars, amino acids, fatty acids.
• Increases insulin release
• Decreases gastric acid secretion

Question 11

Give some key information about somatostatin

Answer 11

• Paracrine
• Stimulates by low pH
• Located in similar area to G cells in antrum of stomach
• Switches off G cells and has a negative effect on gastric acid secretion.