Bile and Bilirubin Metabolism Flashcards
What is bile made of?
Bile salts, bile pigments, bicarbonate, phospholipids and cholesterol.
What are bile salts made from?
Cholesterol derivatives, e.g. Glycholic acid.
What is the function of bile salts?
- Act as emulsifiers to break large lipids to smaller ones to increase the surface area on which Triglyceride lipase can act. They have a hydrophobic face which binds to large triglyceride droplets, and a hydrophillic face which stops large droplets reforming.
Triglyceride —LIPASE–> Monoglyceride + FA’s –LIPASE–> Glycerol + 3FA’s.
- Promote micelle formation as they are a micelle component.
What is a micelle?
Made of bile salts, fatty acids, monoglycerides, phospholipids, cholesterol and fat soluble vitamins (ADEK). They continuously breakdown and reform - while releasing some contents to diffuse across the intestine lining.
How are chylomicrons made?
Triglycerides, phospholipids, cholesterol and proteins are packaged as chylomicrons in the ER of enterocytes. They can then enter lacteals to be transported in the bloodstream.
Phospholipids and proteins make the outer ‘shell’.
In relation to bile pigment production, what happens to RBC’s when they become effate?
Haemoglobin is broken down to Haem + Globin + Fe2+.
How is haem converted to Conjugated Bilirubin? In what cells do these processes happen?
- Reticuloendothelial System cells of the spleen
Haem –HAEMOXYGENASE–> Biliverdin –BILIVERDIN REDUCTASE–> Unconjugated Bilirubin (transported with albumin). - Hepatocytes of the liver via sinusoidal bilirubin transporter
Unconjugated Bilirubin –UDP-GLUCORONYL TRANSFERASE–> Conjugated Bilirubin.
Why is albumin needed to transport unconjugated bilirubin in the blood?
As unconjugated bilirubin is hydrophobic.
What does UDP-glucaronyl transferase do?
Converts unconjugated to conjugated bilirubin by adding Glucaronic Acid.
How is conjugated bilirubin excreted?
It is converted to meso/sterco/urobilinogen by small intestine microflora. This is converted to meso/stero/urobilin by intestinal microflora, all of which can be reabsorbed and recirculated to the liver, then kidney for excretion in the urine. Stercobilin is also excreted in faeces giving it its colour.
How is bile secretion regulated?
Increased pressure in the common bile duct causes bile to flow to the GB where is is stored and concentrated - as epithelial cells remove water and electrolytes.
When fatty acids and amino acids from food enter the duodenum, dupdenal endocrine cells are stimulated to secrete CCK which causes gall bladder SM contraction and causes the Sphincter of Oddi to relax.
Acidic chyme also stimulates S cells to produce Secretin, which causes duct cells of the liver to secrete more bicarbonate in bile and stimulates bile production.
