Gastrointestinal Tract 5 - Liver and Biliary System

Question 1

Liver is the largest internal organ?

Answer 1

True

Question 2

The liver contains how many lobes ? What kind of overall strucure does the liver have?

Answer 2

4 different lobes, hepatic lobule structure

Question 3

Hepatic Lobule Structure

Answer 3

• Hexagonal structure with
• Central vein running through the centre
• Portal triads at each corner

Question 4

Each of the royal triads is composed of:

Answer 4

• Hepatic artery
• Portal vein
• Bile duct

Question 5

Cell types in the liver

Answer 5

1) Epithelial Cells
- Hepatocytes: ~70% of the cells in the liver
- Bile duct epithelium or cholangiocytes: 3-5%

2) Kupffer cells-macrophages
3) Endothelial cells-lining the sinusoids-”fenestrated”

Question 6

Exocrine gland in the liver forms

Answer 6

Forms and secrets bile

Question 7

Liver functions

Answer 7

Metabolism and storage of nutrients
- Liver matches supply to demand (e.g., storage of glucose as glycogen)

Deactivation and detoxification
- Drugs, hormones, waste products, toxicants

Production of circulating proteins
- e.g., blood coagulation factors, lipoproteins

Question 8

Constituents of bile

Answer 8

1. Bile acids-synthesized within the hepatocyte from cholesterol-amphipathic
2. Cholesterol (slightly amphipathic)
3. Salts (e.g., Na+, K+, and HCO3-) and water
4. Phospholipids e.g., phosphatidyl choline-amphipathic
5. Bile pigments e.g., bilirubin
6. Trace metals

Question 9

Pancreatic lipase is a water soluble enzyme and can only work at the surface of lipid droplets,
Therefore

Answer 9

Large lipid droplets need to be made smaller for efficient access by lipase

Question 10

Emulsification

Answer 10

Making large droplets of fat into smaller ones so lipase can have access

Question 11

Emulsification requires

Answer 11

• Mechanical disruption to make lipid droplets smaller (GI motility)
• Emulsifying agent to prevent droplets from re-aggregating
• Amphipathic bile acids
• Phospholipids

Question 12

Bile acids also form “mixed micelles” with

Answer 12

phospholipids and products of lipase digestion (free fatty acids and monoglycerides)

Question 13

“micelle” is a soluble cluster of

Answer 13

amphipathic molecules with nonpolar groups in the middle and polar groups on the outer layer

Question 14

Micelle function

Answer 14

• Micelles keep monoglycerides and fatty acids in small soluble aggregates
• Equilibrium between the micelle and free fatty acid and monoglycerides
• Free forms diffuse across the small intestine epithelium
• Micelles are like a “holding station” for small nonsoluble lipids

Question 15

Which cells produce bile acids?

Answer 15

Hepatocytes

Question 16

The formation of bile is done by:

Answer 16

• hepatocytes: produce bile acids, phospholipids, cholosterol, and bile pigments (into bile canaliculi), via active transport
• bile duct: add HCO3 and H2O to bile.
• gall bladder: stores and concentrates bile
  b/w meals the expels it into duodenum after.

Question 17

Enterohepatic circulation of bile acids

Answer 17

• 20-40 g of bile acids are released into the intestine each day ~ 0.5 g is lost in the feces (95% recovered).
• This recycles the bile acid.

Question 18

What does the enterohepatic circulation of bile acids allow?

Answer 18

Allows the secretion rate to greatly exceed the synthesis rate.

Question 19

Steps for bile acid recycling

Answer 19

1. Bile acids are released by the liver/gall bladder into the duodenum for fat digestion
2. Bile acids are reabsorbed across the small intestine (ileum) into the portal circulation
3. Bile acids are transported back into hepatocytes

Question 20

What causes bile acids to be lost in feces?

Answer 20

Dietary fibre sequesters bile acids preventing them from cycling back to the liver and resulting in their loss in feces

• More bile acids are then synthesized from cholesterol
• Lowers plasma cholesterol

Question 21

Can drugs undergo enterohepatic circulation, and if so which ones?

Answer 21

• Can be beneficial (e.g.,loperamide)

- Can be a disadvantage (reducing bioavailability)

Question 22

What’s regulates hepatobiliary secretion during intestinal phase? And how

Answer 22

• Secretin

Or

• cholecystokinin (chole “bile”, cysto “bladder”, kinin “to move”

Question 23

Where and how is secretin produced?

Answer 23

Secretin is produced and released by S-cells in the duodenum
(Stimulated by acid in the duodenum)

Question 24

How does secretin regulate hepatobiliary secretion during intestinal phase?

Answer 24

Secretin increases HCO3- secretion by the bile duct cells (and the pancreas)

Question 25

How does cholecystokinin regulate hepatobiliary secretion during intestinal phase?

Answer 25

CCK increases contraction of the gall bladder and relaxes the sphincter of Oddi.

• bile is released into the duodenum

Question 26

Where and how is cholecystokinin produced?

Answer 26

Produced by the I cells in the duodenum and jejenum

• Stimulated by digested fats/proteins in upper small intestine

Question 27

Two types of gallstones

Answer 27

• cholesterol stones (majority)

- pigment stones (less common)

Question 28

Cholesterol is water insoluble and only kept in solution in

Answer 28

bile through the formation of micelles with bile acids and phospholipids

Question 29

If the concentration of cholesterol in bile becomes high relative to bile acids, cholesterol starts to

Answer 29

precipitate out , “nucleating” agent also required (e.g., protein, bacteria)

Question 30

Pigment stones

Answer 30

Caused by excessive hemolysis (red blood cell breakdown) which increases bile pigment concentration in bile, pigments form precipitates with Ca2+

Question 31

Gallstones consequences

Answer 31

• Depends on location of stones; may cause obstruction/infection of gall bladder, liver, pancreas
• Pain, nausea, jaundice, malabsorption of fats and fat soluble vitamins

Question 32

Treatment for gallstones?

Answer 32

• Cholecystectomy (removal of gallbladder)
• Need to reduce fat in diet
• Removal of stones
• Drugs to dissolve gallstones