Bile Flashcards
How much bile is produced per day?
500ml each day
What causes the yellow/green colour of bile?
Bilirubin and biliverdin
how much bile do hepatocytes secrete?
60% of bile
How much bile are cholangiocytes responsible for secreting?
40%
How is biliary excretion of bile salts and toxin performed?
Through the use of biliary transporters on the apical and basolateral surfaces of hepatocytes and cholangiocytes
What is the BSEP and what is the purpose of it?
Bile Salt Excretory Pump - Involved in the active transport of bile acids into the bile
What transporters are MDR related proteins?
MRP1 and MRP3
What transports are the products of multi-drug resistance genes?
MDR1 and MDR3
What is MDR1 used to transport?
excretion of xenobiotics and cytotoxins
What are bile acids synthesized from?
Cholesterol
What are the two primary bile acids?
- Cholic acid
- Chenodeoxycholic acid
What are the two secondary bile acids?
- Produced from cholic acid, is deoxycholic acid
- Produced from chenodeoxycholic acid is lithocolic acid
What causes the conversion of primary bile acids into secondary bile acids?
Gut bacterial enzymes
What are bile acids conjugated to?
Glycine and taurine
What are the primary functions of bile acids?
reduce the surface tension of fats and emulsify fats prior to their digestion absorbtion
What is meant by the amphipathic nature of bile salts forming micelles?
They have hydrophobic domains on one surface and hydrophilic domains on the other surface
Describe the organisation of a micelles?
1x surface hydrophilic domains (hydroxyl & carboxyl) - faces OUT → dissolves in water
2nd surface hydrophobic domains (nucleus & methyl) faces IN → dissolves in fat
FFAs & cholesterol INSIDE
What happens to the sphincter of oddi between meals?
Sphincter of oddi is closed, and bile is diverted into the galbladder for storage
What happens to the sphincter of Oddi during eating?
The sphincter of Oddi relaxes which allows the secretion of bile into the duodenum
What causes the galbladder to contract?
- Gastic contents and acidic chyme enter into the duodenum and cause the release of CCK
- CCK binds to CCKa receptors and causes the gall bladder to contract, and release the stored bile into the intestine
What else aside from CCK causes the contraction of the gall bladder?
Ach from the parasympathetic fibres of the vagus nerves
What is the purpose of the gall bladder?
To store bile, concentrate it and acidify it
What are some of the main components of bile?
Water, bile acids, bilirubin, inorganic salts, cholesterol, fatty acids
Where is bilirubin produced from?
The breakdown of heam found in haemoglobin which is found in red blood cells
How is free bilirubin transported around the body?
Bound to albumin
What happens to the bilirubin as it enters the liver?
Bilirubin dissociates from albumin
Undergoes conjugation to form bilirubin diglucuronide (direct bilirubin) - this is done through the conjugation with 2 x UDP-glucuronide molecules
What happens to the bile which enters into the small intestine via the main duodenal papilla?
95% of the bile is absorbed into the terminal ileum through Na + / K+ ATPase pumps and Na+ / Bile co-transporters
What happens to the 95% of the bile which is reabsorbed?
Taken back to the liver via the portal vein in the entero-hepatic circulation system
What happens to the remaining 5% of bile which remains in the small intestine?
converted into secondary bile acids by gut bacteria
What happens to the bilirubin after it enters into the intestine?
- Bilirubin -> Urobilinogen -> Stercobilinogen -> Stercobilin
What happens to stercobilin?
Secreted out the GI systemas faeces - gives the faeces the distinctive brown colour
What percentage of bilirubin is lost in the faeces?
85% is lost in the faeces as stercobilin
How does bilirubin enter into the entero-hepatic circulation?
Bilirubin -> urobilinogen
urobilinogen is then taken back to the liver
How does 1% of the bilirubin end up excreted in the kidneys?
bilirubin -> urobilinogen
urobiligenogen enters into the enterohepatic circulation and taken to liver
then transferred into systemic circulation and taken to kidney, along the way converted into urobilin, which is excreted in the kidney
Describe the faeces and urine of patients with obstructive jaundice?
Faeces - pale - due to lack of sternobilinogen
Urine - darker due to bilirubin
What is an ERCP?
Endoscopic retrograde cholangiopancreatography - is a procedure that combines upper gastrointestinal (GI) endoscopy and x-rays to treat problems of the bile and pancreatic ducts.
What is a PTC?
Percutaneous transhepatic cholangiography - through common hepatic duct
