Bile, bilirubin and jaundice Flashcards
State three roles of bile.
CAT:
- Cholesterol homeostasis, using secretion and excretion to fine-tune serum concentration
- Absorption and digestion, Lipids and lipid-soluble vitamins (ADEK)
- Toxin excretion: Endogenous and exogenous
- Removal of xenobiotics (foreign drug products), drugs and endogenous waste products (e.g. steroid hormones)
List the major components of bile.
What colour is bile
Bile salts, cholesterol, bilirubin, phospholipids, bicarbonate, WATER, enzymes
Bile is an aqueous solution so lots of WATER and other solutes.
Bile is a green colour because of pigments like bilirubin and biliverdin.
How much bile is produced daily?
500 mL
The capacity of the gallbladder = 15-60 mL
Which cell types produce bile? State the relative proportions of bile produced by each cell type.
Hepatocytes - 60%
Cholangiocytes lines the biliary tree, the biliary epithelium - 40%
Describe what happens as the bile travels down the bilary tree
40% bile secreted by cholangiocytes (biliary epithelium)
Alters pH, fluidity and modifies bile as it flows through
H20 drawn INTO bile (osmosis through paracellular junctions)
Luminal glucose and some organic acids also reabsorbed.
HCO3- and Cl- actively secreted INTO bile by CFTR mechanism (Cystic Fibrosis Transmembrane Regulator)
Cholangiocytes contribute IgA by exocytosis
What does bile flow depend on?
The concentration of the bile and salts in the blood
What regulates bile concentration?
The transporters in the cholangiocytes
what does biliary excretion do and where does this take place?
Biliary excretion of bile salts and toxins performed by transporters on apical surface of hepatocytes + cholangiocytes
What channel transports bicarbonate and chloride ions into the bile?
When is bile released?
what does the gall bladder do?
CFTR
Constantly being synthesised. Stored in the gallbladder.
CCK stimulates gall bladder contraction for a big dose.
- Stores bile
- acidifies bile
- concentrates bile (by reabsorbing ions, creating an osmotic gradient) May remove volume
State some of the main transporters that regulate bile concentration.
Bile Salt Excretory Pump (BSEP): active transport of bile acids across hepatocyte canalicular membranes into bile, and secretion of bile acids is a major determinant of bile flow
MDR related proteins (MRP1, MRP3)
MDR1: mediates canalicular excretion of xenobiotics, cytotoxins
MDR 3: encodes a phospholipid transporter protein that translocates phosphatidylcholine from inner to outer leaflet of canalicular membrane
products of the familial intrahepatic cholestasis gene (FIC1) and multidrug resistance genes (MDR1 & MDR3).
What are the primary bile acids and their respective secondary bile acids? What is the difference between primary and secondary bile acids?
- Bile acids are synthesised from cholesterol.
- we have 2 primary and 2 secondary
Primary bile acids are produced by the liver. They are converted to secondary bile acids by the action of colonic bacteria. Deoxycholate is reabsorbed but 99% of lithocholic acid is excreted in the stool.
Primary = Cholic Acid + Chenodeoxycholic Acid
Secondary = Deoxycholic Acid + Lithocholic Acid
What percentage of bile is water?
97%
what is the function of bile?
what special properties does Micelles have?
Reduce surface tension of fats
Emulsify fat preparatory to its digestion/absorption
Bile Salts form Micelles
Bile salts amphipathic
One surface has hydrophilic domains, facing OUT
2nd has hydrophobic domains, facing IN
free Fatty Acids and Cholesterol INSIDE
thus transported to GIT epithelial cells for absorption
what is the effect of high concentrations of bile salts?
Detergent-like actions make bile salts potentially cytotoxic in high concentrations.
what does the right and left lobe of the lung drain into
right lobe drains into the right hepatic duct and the left lobe drains into the left hepatic duct
