The Biliary system

Question 1

What is the biliary tree

Answer 1

The structures responsible for transit and storage of bile

Question 2

Where does the biliary tree start and end/drain into

Answer 2

Starts in the bile canaliculi (adjacent to the hepatocytes)
Drains into the small ductules
1. Small ductules drain into the small bile duct
2. Drains into the small ductules
3. Small ductules -> small bile duct
4. small bile ducts -> larger bile ducts
5. larger bile ducts -> right and left hepatic ducts
6. Hepatic ducts -> common hepatic ducts
7. Common hepatic duct + cystic duct -> common bile duct
8. Common bile duct + pancreatic duct -> ampulla of Vater (duodenal papilla)

Question 3

What is the cystic duct

Answer 3

Connected to the common hepatic duct

Connects the gall bladder to the biliary tree

Question 4

What are the functions of bile

Answer 4

Cholesterol homeostasis
Absorption and digestion of lipids and vitamins (ADEK)
Toxin excretion (endo and exo)

Question 5

How much bile is produced and where

Answer 5

500mL a day
60% from hepatocytes - primary secretion
40% of cholangiocytes - secondary modification

Question 6

Which bile acids are secreted by the liver

Answer 6

Cholic and chenodeoxycholic acid

Amphipathic

Question 7

How do gut bacteria affect bile salts

Answer 7

Convert primary bile acids into secondary bile acids by gut flora
Deoxycholic acid and lithocholic acid

Question 8

Describe the structure of the micelle

Answer 8

Core of TAGs and fatty acids
Surrounded by phospholipids and bile salts
Hydrophilic domain of the bile salt faces out

Question 9

What does the gall bladder do

Answer 9

Stored bile (50mL)
Acidifies bile by absorbing HCO3-
Concentrated bile by reabsorbing ions (can be 80-90%)

Question 10

when is bile released

Answer 10

Constantly synthesised by hepatocytes but stored in the gall bladder
CCK stimulates contraction

Question 11

Where are bile salts mainly absorbed

Answer 11

Terminal portion of the ileum

Question 12

What is the colour of bile due to

Answer 12

Yellow/green

Pigments bilirubin and biliverdin

Question 13

What is bile made up of

Answer 13

Cholesterol, bile salts, bilirubin, drug metabolised, water and other solutes

Question 14

What is the enterohepatic circulation

Answer 14

Substances can cycle between gut and liver by continuous reabsorption in the gut, carriage in the portal blood, hepatocyte secretion into the bile canaliculi and secretion into the common bile duct
80-90% reabsorbed in the ileum

Question 15

Why may the half life of drugs be increased via the enterohepatic circulation

Answer 15

The liver processes some drugs to excrete them via bile but they can get reabsorbed into the SI and re-enter the portal circulation cyclically

Question 16

What is responsible for the colour of faeces

Answer 16

Oxidised stercobilinogen = stercobilin

Question 17

How are bile salts reabsorbed from the portal circulation into the liver

Answer 17

Active transport

Question 18

Where does bilirubin come from

Answer 18

From haemoglobin breakdown in the spleen
(Catabolism of other haem proteins and ineffective bone marrow erythropoiesis)
Carried in the blood via albumin

Question 19

Describe conjugation of bilirubin

Answer 19

Bilirubin is conjugated in the liver by gluconyl transferase (SER)
Produces bilirubin glucoronide/diglucoronide-BR which is water soluble for release into the caniculi

Question 20

What happens to glucoronides after secretion by the bile duct

Answer 20

Excreted into the duodenum
Broken down by bacteria and converted to urobilinogen or stercobilinogen
Some urobilinogen is reabsorbed and excreted by the kidneys in the urine
Urobilinogen is converted by bacteria in the gut to stercobilinogen
Most of the stercobilinogen is oxidised to stercobilin

Question 21

What is the role of the biliary tree

Answer 21

alters pH, fluidity and bile
H2O into the bile through paracellular junctions
HCO3- and Cl- actively secreted into bile by CFTR
reabsorption of sugars and acids
exocytosis of IgA

Question 22

What is the cause of cholestasis

Answer 22

Dysfunction of transporters on the apical surface of hepatocytes and cholangiocytes e.g. BSEP, MRP1, MRP3, FIC1

Question 23

How is bile secretion into the duodenum controlled

Answer 23

Sphincter of Oddi at the Ampulla of Vater, stimulated by CCK

Question 24

What happens when bile is stopped from entering the gut

Answer 24

Up 5o 50% ingested fat appears in faeces

Malabsorption of fat soluble vitamins ADEK