Physiology of the accessory organs

Question 1

Which pancreatic structures have exocrine functions?

Answer 1

Acinar cells, grouped into lobules and connected by intercalated ducts

Question 2

Describe and explain how enzymes are stored in the pancreas

Answer 2

Enzymes are stored in acinar cells as zymogens (inactive precursors) to prevent autodigestion of the pancreas

Question 3

Which is the main enzyme that converts zymogens to active enzymes?

Answer 3

Trypsin

Question 4

Which enzyme converts trypsinogen to trypsin?

Answer 4

Enterokinase; an enzyme bound to the brush border of duodenal enterocytes
(N.B. trypsin also converts trypsinogen to trypsin)

Question 5

Describe the effect of gastric contents (chyme) being present in the duodenum

Answer 5

1) presence of acid in the duodenum stimulates release of secretin (which stimulates bicarbonate secretion)
2) presence of fat and/or amino acids in duodenum stimulates release of cholecystokinin (CCK) (which stimulates zymogen secretion from pancreas)

Question 6

What is the function of the gallbladder?

Answer 6

Stores and concentrates bile

Question 7

Describe the role of secretin

Answer 7

Decreases acid secretion
- inhibits secretion of gastrin
Delays gastric emptying
Increases duodenal, pancreatic and bile duct bicarbonate secretions

Question 8

Describe the mechanism by which bile is reabsorbed

Answer 8

95% of bile acids are reabsorbed by active transport in the ilium
They are then recycled back to the liver via the hepatic portal system for further secretion into biliary system and gallbladder

Question 9

Describe the mechanisms controlling the storage and release of bile to/from the gallbladder

Answer 9

Sphincter of Oddi

• controls release of bile and pancreatic juices into the duodenum
• when contracted (closed), bile is forced back into the gallbladder

Cholecystokinin (CCK)

• released in response to the presence of fat in the duodenum
• causes sphincter of Oddi to relax
• causes gallbladder to contract

Question 10

How does the gallbladder concentrate bile?

Answer 10

The gallbladder concentrates bile by factor of 5 - 20 by absorbing sodium ions and water

Question 11

Give four major functions of the exocrine pancreas

Answer 11

1. Bicarbonate secretion
   - stimulated by Secretin in response to the presence of HCl in the duodenum
2. Alpha-amylase secretion
3. Lipase secretion
   - stimulated by CCK in response to the presence of acid in the duodenum
4. Protease secretion
   - trypsinogen and chymotrypsinogen
   - stimulated by CCK in response to the presence of peptides in the duodenum

Question 12

Which parts of the pancreas secrete bicarbonate?

Answer 12

Duct cells (not the acinar cells!)

Question 13

Which hormone controls the secretory function of acinar cells in the pancreas?

Answer 13

Cholecystokinin (CCK) - stimulates enzyme secretion

Question 14

Which hormone controls the secretory function of cuboidal duct cells in the pancreas?

Answer 14

Secretin - stimulates bicarbonate secretion

Question 15

Give four types of proteins that are produced by the liver

Answer 15

Carrier proteins - albumin and transferrin
Immune system proteins - complements and CRP
Hormones - thrombopoetin, angiotensinogen, IGF
Clotting factors - prothrombin and fibrinogen

Question 16

Give three processes carried out by hepatocytes as part of carbohydrate metabolism

Answer 16

Glycogenesis
Glycogenolysis
Gluconeogenesis

Question 17

What happens to the products of deamination and transamination?

Answer 17

Ammonia is fed into the urea cycle and is converted to urea which is then excreted
Non-nitrogenous parts are converted to glucose or lipids

Question 18

Give four major functions of the liver

Answer 18

Metabolism
Storage (carbs and fat)
Detoxification (cytochrome P450 system)
Bile production