GIT Lec 5: Liver + Biliary system

Question 1

The liver

Answer 1

• is the largest internal organ of body (2.5% of body weight)
• contains 4 different lobes
• receives 25% of cardiac output
• extends across the entire abdominal cavity

Question 2

ducts (liver)

Answer 2

-common hepatic duct –> common bile duct –> pancreatic duct

Question 3

hepatic lobule is

Answer 3

the building block of the liver

Question 4

hepatic lobule structure

Answer 4

-hexagonal structure with central vein in the middle, portal triads at each corner

Question 5

portal triad composed of

Answer 5

hepatic artery, portal vein, bile duct

Question 6

liver sinusoids

Answer 6

vessels in hepatic lobule in which blood from hepatic artery and portal vein mix

Question 7

cell types liver

Answer 7

• epithelial cells (hepatocytes- 70%, bile duct epithelium (cholangiocytes)- 3-5%)
• kupffer cells - specialized macrophages
• endothelial cells-lining the sinusoids- “fenestrated”- leaky

Question 8

major functions of the liver

Answer 8

• exocrine gland: formation + secretion of bile
• metabolism +storage of nutrients (liver matches supply to demain) ex. glucose –> glycogen
• deactivation + detoxification (drugs, hormones, waste, toxicants)
• production of circulating proteins (blood coag factors, lipoproteins)

Question 9

Constituents of bile

Answer 9

1. bile acids
2. cholesterol (amphipathic)
3. salts (eg. Na+, K+,HCO3-), H2O
4. phospholipids (ex. phosphatidyl choline - amphipathic)
5. bile pigments (ex. bilirubin- breakdown product of heme)
6. trace metals

Question 10

bile acids synthesized by

Answer 10

hepatocytes from cholesterol–> amphipathic

Question 11

pancreatic lipase is water soluble so

Answer 11

It works only at surface of lipid droplets

Question 12

emulsification

Answer 12

-large lipid droplets made into smaller droplets

Question 13

emulsification requires

Answer 13

• mechanical disruption to make lipid droplets smaller

- emulsifying agents to prevent re-aggregating (amphipathic bile acids/phospholipids)

Question 14

bile acids and phospholipids +products of lipase digestion which are …. form

Answer 14

• free fatty acids, monoglycerides

- mixed micelles

Question 15

pure phospholipids can’t form micelles because

Answer 15

steric hindrance

-liposome instead

Question 16

micelles keep free fatty acids, monoglycerides

Answer 16

in small soluble aggregates —“holding station”

Question 17

equilibrium between micelle + free fatty acids, monoglycerides (consequence)

Answer 17

free forms diffuse across the small intestine epithelium

Question 18

formation of bile (cells)

Answer 18

• hepatocytes - produce + secrete bile acids (from cholesterol), secrete phospholipids, cholesterol + bile pigments -primary active transport)
• bile duct cells- HCO3- (and other salts)+ H2O to bile
• gallbladder- stores + concentrates bile between meals +exprels after one

Question 19

bile acid released amount and in feces (recovery)

Answer 19

• 20-40 g of bile acid released

- 0.5 g in feces (95% recovered)

Question 20

enterohepatic circulation

Answer 20

recycling of bile acids– reabsorbed in ileum into portal circulation into hepatocytes
- so secretion rate greater than synthesis rate

Question 21

fibre consequences on enterohepatic circulation

Answer 21

-Sequesters bile acids, lose more to feces and more bile acids created lowering plasma cholesterol

Question 22

drugs in enterohepatic circulation benefits + disadvantages

Answer 22

benefits: remains in place of action
disadvantages: reduces bioavailability

Question 23

secretin- regulation of hepatobiliary secretion

Answer 23

increased HCO3- secretion by bile duct cells/pancreas

Question 24

CCK- regulation of hepatobiliary secretion

Answer 24

increased contraction of gallbladder + relaxes sphincter of Oddi

Question 25

gallstones (cholesterol stones)- majority

Answer 25

- cholesterol is water-insoluble, kept in solution by micelles - increases cholesterol in bile to precipitate out (nucleating agent: proteins, bacteria)

Question 26

gallstones (pigment stones)- less common

Answer 26

- caused by excessive hemolysis | - increased in bile pigments, precipitate out with Ca2+

Question 27

consequences of gallstones

Answer 27

- may cause obstruction, infection of gallbladder, liver, pancreas - pain, nausea, jaundice, malabsorption of fat/ fat soluble vitamins

Question 28

treatment of gallstones

Answer 28

- cholecystectomy (removal of gallbladder) - removal of stones - drugs to dissolve stones

Question 29

bile canaliculus

Answer 29

-thin tubes that receive bile from hepatocytes then drain into cholangiocytes bile duct