Lecture 24: Gastrointestinal 2 - Accessory Organs

Question 1

Describe the contributions of the 3 major accessory glands

Answer 1

Liver: synthesizes bile
Gallbladder: stores bile
Pancrease: secretes HCO3-, trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase A and B, amylase, lipase, monitor peptide

Question 2

Describe the composition and control of pancreatic secretions

Answer 2

trypsinogen converted to trypsin by enterokinase, trypsin can convert all the other enzymes to their active form

HCO3- gets brought into cell by NBC (sodium bicarbonate cotransporter) or converted by carbonic anhydrase. leaves via HCO3/Cl exchanger.

Question 3

Explain when and where secretin and cholecystokinin are synthesized, and what their function is

Answer 3

secretin synthesized by S cells in response to low pH sensed in the duodenum. results in increased bicarbonate secretion. Acts on CFTR channels to increase HCO3- secretion by increased cAMP levels, acts on SCTR channels to increase cAMP via Gs pathway and increase release of the other pancreatic enzymes

Cholecystokinin synthesized by I cells in response to CCK release peptide (from sensing fats or protein) or monitor peptide from the pancreas. CCK binds to CCK-1 receptor to increase calcium and cause release of pancreatic products. CCK also mediates relaxation of the Sphincter of Oddi.

Both are produced in the duodenum and go through blood stream to pancreatic acinar cells

Question 4

Explain how gastric emptying is regulated

Answer 4

CCK delays gastric emptying. also depends on what is eaten. glucose leads to high rate of emptying, protein takes longer. regulated by small intestine, both neurally and hormonally.