Bile And Bilirubin Flashcards
What is the composition of bile?
Bile Salts- 50% (taurocholic or glycocholic acid) Lecithin- 40% Cholesterol Bilirubin- gives bile its color Water and ions
What is the function of bile?
To emulsify fats to increase their surface area for lipase action
Explain the production of 1º bile acids? Which is more common?
Cholesterol converted to 7 alpha hydroxycholesterol via the rate limiting enzyme, 7 alpha hydroxylase
7a-hydroxycholesterol converts to 1º bile acids, cholic or chenodeoxycholic acid
Cholic acid > chenodeoxycholic acid
How are bile salts created? What are the 2 main bile salts?
Bile acids are conjugated with glycine or taurine to form bile salts
Glycocholic acid and taurocholic acid
What two transporters secrete bile salts from hepatocytes through bile canaliculi?
MRP2 and BSEP
What affect does secretin have on bile as it travels to the gallbladder?
Secretin causes HCO3 to be secreted into the bile which increases its volume but decreases its concentration; once in the gallbladder the ions will be reabsorbed to concentrate bile
What hormone triggers the secretion of bile? How does it work?
CCK triggers gallbladder contraction and relaxation of the sphincter of oddi to secrete bile into the duodenum to emulsify lipids for digestion
Within the small intestines how are bile salts converted into 2º bile acids? What are the bile acids and which is more common?
Within the small intestines, bacterial enzymes will deconjugate bile salts into 2º bile acids
Deoxycholic acid > lithocholic acid
How are 2º bile acids absorbed into ileal enterocytes?
ASBT (Na/BA cotransporter) reabsorbs bile acids from the ileum into enterocytes
How do bile acids enter the enterohepatic circulation from enterocytes?
Bile acids enter the enterohepatic circulation via OST alpha or beta transporters
How are bile acids reabsorbed from enterohepatic circulation into hepatocytes?
Bile acids cross fenestrated endothelium and are reabsorbed into hepatocytes via NTCP (Na/BA cotransporter) or OATP transporters to be conjugated and recylced
Explain the negative feedback system involved in bile synthesis
Increase bile secretion -> increase bile reabsorption -> feedback inhibit 7a-hydroxylase activity
Explain what happens if enterohepatic circulation is disrupted; what are some possible causes of this disruption?
If enterohepatic circulation is disrupted then less bile is recycled and thus more is excreted. To account for the loss in bile, 7a-hydroxylase is induced and cholesterol is used to synthesize bile
Possible causes include bile acid binding resins which are used to lower LDL or ileal resections
Why are ileal resections associated with steatorrhea?
Ileal resections disrupt the enterohepatic circulation meaning excessive amounts of bile are excreted. The amount lost is greater than the maximum amount of bile we can synthesize and thus we have malabsorption of lipids which leads to fatty stools
Explain RES systems involvment in bilirubin production. Where does bilirubin go once created and how so?
RBC -> hemoglobin -> biliverdin -> bilirubin
Bilirubin enters blood stream and binds albumin
