Digestive Secretions

Question 1

What is the sphincter of Oddi?

Answer 1

It can close off the common duct through which bile and secretions from the pancreas enter the duodenum, and relaxes in response to CCK-PZ, allowing the secretions to enter the duodenum and mix with the food.

It serves to regulate the flow of bile and pancreatic juices as well as to prevent the reflux of duodenal contents into the pancreatobiliary system.

Question 2

What is the name of the little prominence where the common duct enters the duodenum? It is important to endoscopists!

Answer 2

The Ampulla of Vater

Question 3

What happens to the bile when the sphincter of Oddi is not open?

Answer 3

The bile is then stored in the gall bladder until needed.

Question 4

What are APUD cells?

Answer 4

Amine Precursor Uptake and Decarboxylation – neuroendocrine cells

Question 5

What is the source, stimulus, pathway and 1st target of Gastrin?

Answer 5

G-cells

Neural, aa, peptides

endocrine

ECL and parietal cells

Question 6

What is the source, stimulus, pathway and 1st target of Cholecystokinin?

Answer 6

Duodenum (I cells)

Fatty acids + some aa

endocrine + paracrine

Vagal afferent terminals

Gallbladder

Question 7

What is the source, stimulus, pathway and 1st target of Secretin?

Answer 7

Duodenum
(S cells)

Acid in SI

endocrine + paracrine

Vagal afferent terminals
Pancreatic duct cells
Cholangiocytes

Question 8

What is the source, stimulus, pathway and 1st target of Motilin?

Answer 8

Intestine

Neural, fasting

Paracrine

Upper GI motility

Question 9

What is the source, pathway and 1st target of Vasoactive intestinal peptide?

Answer 9

Nerve terminals

Neurocrine

Smooth muscle secretory cells.

Question 10

What is the difference between CCK-A receptors and CCK-B receptors?

Answer 10

CCK-A receptors are better for CCK, CCK-B receptors are better for gastrin

Question 11

What are the two main effects of Cholecystokinin-Pancreozymin (CCK)?

Answer 11

Stimulation of pancreatic secretion (acinar)

Stimulation of gallbladder emptying

Question 12

What can Secretin inhibit?

Answer 12

gastric acid production

Question 13

What is the main effect of secretin?

Answer 13

Main effect is to stimulate bicarbonate secretion by ductal cells in the pancreas and liver

Question 14

What are 4 facts about bile?

Answer 14

Synthesised by the liver
Recycled (up to 8 times a day!)
Amphipathic – polar groups are all on one side
Form micelles at high concentration

Question 15

What are the steps on the hepatic synthesis of glycine (a bile salt)?

Answer 15

Cholesterol>cholic acid>deoxycholic acid>glycine

Question 16

What are the steps on the hepatic synthesis of taurine (a bile salt)?

Answer 16

Cholesterol>chenodeoxycholic acid>lithocholic acid>taurine

Question 17

What are hepatocytes sandwiched between?

Answer 17

Blood and Bile

Question 18

What do hepatocytes actively secrete?

Answer 18

Bile components

• bile acids
• phosphatidylcholine
• conjugated bilirubin
• xenobiotics

Question 19

What happens as bile flows along the bile ducts?

Answer 19

Bicarbonate, salt and water are added.

The process is stimulated by secretin, with minor effects from glucagon and VIP.

Note the presence of CFTR

Question 20

What is the implication of bile components forming micelles?

Answer 20

The fluid remains isotonic

Question 21

How does acidification of the bile reduce the risk of gallstones?

Answer 21

Net proton secretion acidifies the bile, reducing the risk of precipitation of Ca++ (and other) salts. This reduces the risk of gallstones

Question 22

What 5 proteases does the pancreas secrete?

Answer 22

Trypsinogen
 Chymotrypsinogen
 Proelastase
 Procarboxypeptidases A and B
 (Trypsin inhibitors)

Question 23

What pancreatic lipases does the pancreas secrete?

Answer 23

Pancreatic lipase
Nonspecific esterase
Prophospholipase A2
(Procolipase)

Question 24

Mutations in which channel lead to cystic fibrosis?

Answer 24

CFTR channel (transports Cl- out of cell)

In CF, pancreatic secretions are thick and sticky, leading to pancreatic failure and the need for dietary supplementation with pancreatic enzymes

Question 25

Via which nerve is duct secretion potentiated by CCK?

Answer 25

Duct secretion is strongly stimulated by secretin. This is potentiated by CCK (via Vagus nerve).