GI endocrinology

Question 1

What is the difference between acinar cells and duct cells?

Answer 1

•Acinar cells

–Serous cells = protein part including enzymes + ionic solutions

–Mucous cells = mucins

•Duct cells = modify ionic concentrations

General principle: Acinar cells secrete and duct cells modify

Question 2

What enzyme cleaves pepsinogen to pepsin?

Answer 2

Trick question - there isn’t one - it’s the acidic environment that causes it to cleave.

Question 3

What cells (3) are unique to the epithelium in the body/oxyntic region of the stomach and what do they secrete?

Answer 3

~parietal cells - HCl, intrinsic factor

~chief cells - pepsinogen

~ECL cells - histamine

Question 4

What cells (2) are unique to the epithelium in the pyloric region of the stomach and what do they secrete?

Answer 4

~neuroendocrine G cells - gastrin (increase digestion)

~neuroendocrine D cells - somatostatin (slow down digestion)

Question 5

What is the alkaline tide?

Answer 5

In acid-secreting parietal cells, for each H+ pumped into lumen, one HCO3- enters blood

Question 6

How do we deal with the alkaline tide? (can’t have highly alkaline blood for long)

Answer 6

Pancreas releases bicarb from the blood into the small intestine tract to neutralize the H+ flood from the stomach

Question 7

How is stomach acid secretion regulated?

Answer 7

• Four chemical messengers regulate the insertion of H+/K+ -ATPase into plasma membrane: ACh, gastrin, histamine, and somatostatin
• Parietal cells contain receptors for all four agents (go: ACh, gastrin, histamine; stop: somatostatin)

Question 8

ACh: who releases? what receptors?

Answer 8

ACh released by vagus or enteric neurons acting on mAChR (M3)

Question 9

Gastrin: who releases? what receptors?

Answer 9

Gastrin released by G cells in antrum and duodenum acting on CCKB receptor

Question 10

Histamine: who releases? what receptors?

Answer 10

Histamine released by ECL cells acting on H2 receptor

Question 11

Somatostatin: who releases? what receptors?

Answer 11

Somatostatin released by D cells in antrum and duodenum acting on SSTR2 receptor

Question 12

What are the three phases of gastric acid secretion?

Answer 12

~cephalic (taste, smell, thought of food -> medulla oblongata -> vagus -> increase in gastric secretion)

~gastric (distention of stomach -> increase of gastric secretion)

~intestinal (chyme containing lipids, amino acids, lots of H+ signals medulla oblongata to decrease gastric secretion)

Question 13

What hormones released by the duodenum inhibit gastric secretions in the stomach?

Answer 13

secretin

CCK (cholecystokinin)

Question 14

Which hormone is dominant in the cephalic phase?

Answer 14

CCK

Question 15

Which hormone is dominant in the intestinal phase?

Answer 15

secretin

Question 16

CCK and secretin inhibit gastric secretions; what are their effects at the pancreas?

Answer 16

stimulate enzyme secretion

Question 17

What does cholera do that causes disease?

Answer 17

choleratoxin binds Gs protein -> increase cAMP -> insertion and opening of CFTR chloride channel -> increases cAMP -> chloride is going to be lost in huge quantities -> diarrhea

Question 18

What substance stimulates secretion of bile from gallbladder?

Answer 18

CCK (contracts gallbladder)

Question 19

What substance stimulates secretion of digestive enzymes from pancreas?

Answer 19

CCK (relaxes sphincter of Oddi)

Question 20

What are two devastating effects of diseases that disrupt the terminal ileum, such as Crohn’s?

Answer 20

1. poor bile reuptake, which mostly occurs here
2. poor B12-IF absorption, which occurs here

Question 21

What is the problem that occurs in the gut in cystic fibrosis?

Answer 21

decreased secretions of chloride = impaired flow and mucosa of intestine

Cystic fibrosis = abnormal function of CFTR chloride channel