Bile Secretion Flashcards
What is bile required for?
Digestion and absorption of many fats and fat-soluble vitamins
Excretion of water-insoluble substances such as cholesterol and bilirubin
What are primary and secondary bile acids?
Primary - synthesized in liver from cholesterol
Secondary - converted fraction of primary acids by bacteria
What are bile salts?
Bile acids conjugated with glycine/taurine and Na ions
More water soluble at intestinal pH
Ionized at physiologic pH and not passively absorbed
Amphipathic, so emulse fats
What phospholipids are present in bile?
Lecithins, solubilized by bile salt micelles
Makes solubility of other lipids more effective
What happens if there is more cholesterol in bile that can be solubilized?
Crystals form in bile, may serve as seed for gallstone formation
What is bilirubin?
Principal pigment in bile
Insoluble until conjugated with glucuronic acid in liver
Secreted from liver as soluble salt bilirubin glucuronide
What is jaundice?
Yellowish tint of body tissues
Due to large quantities of bilirubin in plasma
Caused by increased hemolysis, obstruction of bile duct, or damage to liver
What is the apical sodium-dependent bile salt transporter?
ASBT is responsible for absorbing most bile salts in the terminal ileum
Bile acids bind to ileal bile acid binding protein in enterocyte
Enter portal blood via organic solute transporter (OST)
What is sodium-taurocholate cotransporting peptide (NTCP)?
Hepatocytes use it to extract bile salts along with Na from the portal blood
How do bile acids get transported back into the bile duct?
Via ATPase-dependent bile salt export pump (BSEP) and some via MRP2
What can result from defects in BSEP?
Cholestasis - reduction in or lack of bile flow
What occurs to bile salts not reabsorbed in small intestine?
Excreted in feces, rate of bile salt synthesis determined by rate of return to liver
What is the bile-independent fraction of biliary secretion?
Refers to volume of secretion of water and electrolytes
Secretin stimulates secretion of HCO3 and water
What is the bile-dependent fraction of biliary secretion?
Refers to quantity of bile salts secreted by liver
Related to amount reabsorbed by the liver
Bile salts and bile Acids inhiit new vile acid synthesis
What are choleretics?
Potent stimulators of bile secretion
Bile salts and acids act at choleretics
What are the functions of the gallbladder?
Storage - collects and concentrates bile by removing Na, Cl, and HCO3
Contraction - stimulated by CCK (acts directly on smooth muscle, and vagus/intrinsic nerves)
CCK also relaxes the sphincter of oddi
What are the two types of gallstones?
Cholesterol and Pigment stones
What are cholesterol gallstones?
Most gallstones in western society
Cholesterol crystallized because of supersaturation, act as nucleus for stone formation
What are pigment gallstones?
Composed of calcium bilirubinate
Bilirubin becomes unconjugated, which is now insoluble in bile
Precipitates with Ca to begin stone-forming process
What is a cholecystectomy?
Surgical removal of gallbladder
Normal digestion unaffected, bile empties slowly, but continuously from liver
Fats can be digested, but high fat food should be avoided
