GI Hormones

Question 1

Gastrin secretion, stimulation, inhibition, and actions

Answer 1

Secreted from G cells located in the antrum, duodenum and jejunum after eating a meal.

» Stimulation - products of protein digestion, stomach distention and vagal stimulation (GRP or bombesin).

» Inhibition - low pH of the gastric contents.

Actions:
• stimulates H+ secretion by gastric parietal cells
• growth of gastric mucosa (trophic effect)

Question 2

Cholecystokinin (CCK) secretion, stimulation, and actions

Answer 2

Secreted from I cells located in mucosa of the duodenum, jejunum and ileum.

» Stimulation - monoglycerides and fatty acids or small peptides and amino acids.

Actions:
• contracts gallbladder, relaxes sphincter of Oddi -> bile secretion
• secretion of bicarbonate and enzymes from the pancreas
• trophic (stimulating) effects on exocrine pancreas and gallbladder
• inhibits/slows gastric emptying

Question 3

Secretin secretion, stimulation, and actions

Answer 3

Secreted by the S cells in the duodenum, jejunum and ileum.

» Stimulation - H+ and fatty acids

Actions:
• increases pepsin secretion (pepsin helps to digest the protein that you consume in food)
• increases pancreatic and biliary bicarbonate secretion
• trophic effect on pancreas
• inhibits gastric H+ secretion

Question 4

Gastric inhibitory peptide secretion, stimulation, and actions

Answer 4

Secreted by K cells in duodenum and proximal jejunum.

» Stimulation - oral glucose, amino acids and fatty acids.

Actions:
• stimulates insulin secretion by the pancreatic beta (β) cells
• inhibits gastric H+ secretion

Question 5

Motilin secretion and actions

Answer 5

Secreted by M cells of duodenum and jejunum during fasting.

Actions:
• Increases smooth muscle contraction in stomach and small intestine
• Relationship with the migrating motility complex (a distinct pattern of electromechanical activity observed in gastrointestinal smooth muscle during the periods between meals. It is thought to serve a “housekeeping” role and sweep residual undigested material through the digestive tube.)

Question 6

Ghrelin secretion and actions

Answer 6

Secreted by oxyntic cells of stomach (some in small intestine)

Actions:
• Stimulates growth hormone secretion (also known as somatotropin, is a peptide hormone that stimulates growth, cell reproduction, and cell regeneration in humans)
• Regulates energy balance

Question 7

GLP-1 secretion and actions

Answer 7

Produced by cleavage of glucagon (also can produce GLP-2) in small intestine

Actions:
• Antihyperglycemic
• Inhibits gastric secretion and motility

Question 8

Leptin secretion and actions

Answer 8

Released by adipocytes (white fat cells)

Actions:
• Regulates body weight (inhibits NPY cells and stimulates POMC cells in hypothalamus)

Extra info:

• NPY (neuropeptide Y) functions: increasing food intake and storage of energy as fat, reducing anxiety and stress, reducing pain perception, affecting the circadian rhythm, reducing voluntary alcohol intake, lowering blood pressure, and controlling epileptic seizures
• POMC functions: produces peptides such as ACTH (helps maintain blood sugar levels, protects the body from stress, and stops (suppresses) inflammation.)