Pancreas and Liver

Question 1

What are 3 things added to chyme in duodenum?

Answer 1

• Adding water to reduce hypertonicity
• Secretions from Pancreas (HCO3, enzymes)
• Secretions from liver (HCO3, Bile)

Question 2

Why is chyme hypertonic? (compared to plasma)

Answer 2

• Food produces many solutes that are dissolved in gastric juice
• Stomach wall is impermeable to water

(Duodenum is relatively permeable to water, and chyme is isotonic when it leaves the duodenum)

Question 3

The pancreas is 90% Exocrine and 2% Endocrine.

Describe its innervation

Answer 3

Sympathetic;
- Inhibition

Parasympathetic;

• Vagus simulation
• Hormones

Question 4

Describe the basic structure of the exocrine portion of the pancreas

Answer 4

• Acinus
• Centroacinar cells (Aqueous component of secretion)
• Duct (modifies aqueous secretion)

Question 5

Describe the stimulation of the Acinus to produce secretions

Answer 5

• Stimulated by Vagus and CCK (from I cells in duodenum)

- Upon detection of small peptides/ fats/ hypertonicity in duodenum

Question 6

List 3 enzymes secreted by Acinus (help with digestion and acid neutralisation)

Answer 6

• Amylases, in active form
• Lipases, in active form
• Proteases, in inactive form (Trypsin, Chymotrypsin, Elastase, Carboxypeptidase etc)

Question 7

Describe the formation and release of Acinar secretions

Answer 7

• Formed on RER, moved to Golgi complex
• Condensed into zymogen granules
• ZGs released with appropriate stimulus (CCK/ Parasympathetic)

Question 8

What does the Pancreatic duct join with to enter into duodenum

Answer 8

Pancreatic duct + Bile duct from gall bladder-> Common Bile Duct which empties into duodenum at the Ampulla of Vater

Question 9

Describe the vasculature of the liver

Answer 9

• Blood from hepatic portal vein and hepatic artery drain into central vein
• Central veins combine to form Hepatic veins-> IVC

Question 10

Describe the movement of bile in liver

Answer 10

• Bile made in hepatocytes, flow out of liver in Canaliculi
• Canaliculi join-> Bile ducts
• Ducts join-> Common bile duct

Question 11

Compare the 2 components of bile

Answer 11

Bile acid dependent component;

• Secreted into Canaliculi by hepatocytes
• Contains bile acids + pigments

Bile acid independent component;

• Secreted by duct cells
• Similarly to pancreatic duct cell secretions, solution is alkaline and stimulated by secretin

Question 12

What are the 2 primary bile acids?

What are bile salts?

Answer 12

• Choline acid
• Chenodeoxycholic acid

Bile acids that are conjugated with amino acids (such as glycine and taurine)

Question 13

Why do we need bile salts sometimes as opposed to bile acids?

Answer 13

• Bile acids are not always soluble at duodenal pH (Salts generally are)
• Bile salts have an Amphipathic structure (Hydrophobic and Philic ends)

Question 14

What is the significance of bile salts having an amphipathic structure?

Answer 14

• Can act at oil/ water surface

- Crucial for emulsification of dietary lipids

Question 15

Describe fat digestion with reference to Bile acids

Answer 15

• Lipids tend to form large globules by the time they reach duodenum, reducing SA for enzymes (Lipases) to act
• Bile acids/ salts emulsify fat into smaller units to increase SA
• Bile acids then form Micelles containing products of lipid breakdown

Question 16

Describe fat digestion after Micelle formation

Answer 16

• Lipid breakdown products diffuse into intestinal epithelial cells
• Inside enterocyte, re-esterified and packaged with apoproteins to form Chylomicrons
• Exocytosis of Chylomicrons into lymph capillaries/ Lacteals (too large to enter blood capillaries)
• Later, re enter vascular system

Question 17

Describe the circulation of bile acids/ salts

Answer 17

• Don’t enter enterocytes with lipids, but remain in gut lumen
• Reabsorbed in terminal Ileum and return to liver in portal blood, where the liver extracts the bile salts for re-use

Question 18

Bile is always being produced but where is it stored?

What else happens to bile here?
What can it lead to?

Answer 18

• Gallbladder
• Concentrates bile (removes water and ions)
• Gallstones

(CCK from duodenum stimulates gallbladder contraction and relaxation of Sphincter of Oddi)

Question 19

What is Steatorrhea?

Explain how does this present?

Answer 19

This is when bile acids/ salts or pancreatic Lipases are not secreted adequately

Fat in faeces (not enough lipids absorbed);

• Pale
• Floating
• Foul smelling

Question 20

What breakdown product is secreted into bile then excreted in faeces?

What can it lead to if not excreted?

Answer 20

Bilirubin from RBCs

Jaundice, if accumulates in blood