The Biliary system Flashcards
What is the biliary tree
The structures responsible for transit and storage of bile
Where does the biliary tree start and end/drain into
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)
What is the cystic duct
Connected to the common hepatic duct
Connects the gall bladder to the biliary tree
What are the functions of bile
Cholesterol homeostasis
Absorption and digestion of lipids and vitamins (ADEK)
Toxin excretion (endo and exo)
How much bile is produced and where
500mL a day
60% from hepatocytes - primary secretion
40% of cholangiocytes - secondary modification
Which bile acids are secreted by the liver
Cholic and chenodeoxycholic acid
Amphipathic
How do gut bacteria affect bile salts
Convert primary bile acids into secondary bile acids by gut flora
Deoxycholic acid and lithocholic acid
Describe the structure of the micelle
Core of TAGs and fatty acids
Surrounded by phospholipids and bile salts
Hydrophilic domain of the bile salt faces out
What does the gall bladder do
Stored bile (50mL)
Acidifies bile by absorbing HCO3-
Concentrated bile by reabsorbing ions (can be 80-90%)
when is bile released
Constantly synthesised by hepatocytes but stored in the gall bladder
CCK stimulates contraction
Where are bile salts mainly absorbed
Terminal portion of the ileum
What is the colour of bile due to
Yellow/green
Pigments bilirubin and biliverdin
What is bile made up of
Cholesterol, bile salts, bilirubin, drug metabolised, water and other solutes
What is the enterohepatic circulation
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
Why may the half life of drugs be increased via the enterohepatic circulation
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
What is responsible for the colour of faeces
Oxidised stercobilinogen = stercobilin
How are bile salts reabsorbed from the portal circulation into the liver
Active transport
Where does bilirubin come from
From haemoglobin breakdown in the spleen
(Catabolism of other haem proteins and ineffective bone marrow erythropoiesis)
Carried in the blood via albumin
Describe conjugation of bilirubin
Bilirubin is conjugated in the liver by gluconyl transferase (SER)
Produces bilirubin glucoronide/diglucoronide-BR which is water soluble for release into the caniculi
What happens to glucoronides after secretion by the bile duct
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
What is the role of the biliary tree
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
What is the cause of cholestasis
Dysfunction of transporters on the apical surface of hepatocytes and cholangiocytes e.g. BSEP, MRP1, MRP3, FIC1
How is bile secretion into the duodenum controlled
Sphincter of Oddi at the Ampulla of Vater, stimulated by CCK
What happens when bile is stopped from entering the gut
Up 5o 50% ingested fat appears in faeces
Malabsorption of fat soluble vitamins ADEK
