Bile Secretion

Question 1

What is bile required for?

Answer 1

Digestion and absorption of many fats and fat-soluble vitamins

Excretion of water-insoluble substances such as cholesterol and bilirubin

Question 2

What are primary and secondary bile acids?

Answer 2

Primary - synthesized in liver from cholesterol

Secondary - converted fraction of primary acids by bacteria

Question 3

What are bile salts?

Answer 3

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

Question 4

What phospholipids are present in bile?

Answer 4

Lecithins, solubilized by bile salt micelles

Makes solubility of other lipids more effective

Question 5

What happens if there is more cholesterol in bile that can be solubilized?

Answer 5

Crystals form in bile, may serve as seed for gallstone formation

Question 6

What is bilirubin?

Answer 6

Principal pigment in bile

Insoluble until conjugated with glucuronic acid in liver

Secreted from liver as soluble salt bilirubin glucuronide

Question 7

What is jaundice?

Answer 7

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

Question 8

What is the apical sodium-dependent bile salt transporter?

Answer 8

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)

Question 9

What is sodium-taurocholate cotransporting peptide (NTCP)?

Answer 9

Hepatocytes use it to extract bile salts along with Na from the portal blood

Question 10

How do bile acids get transported back into the bile duct?

Answer 10

Via ATPase-dependent bile salt export pump (BSEP) and some via MRP2

Question 11

What can result from defects in BSEP?

Answer 11

Cholestasis - reduction in or lack of bile flow

Question 12

What occurs to bile salts not reabsorbed in small intestine?

Answer 12

Excreted in feces, rate of bile salt synthesis determined by rate of return to liver

Question 13

What is the bile-independent fraction of biliary secretion?

Answer 13

Refers to volume of secretion of water and electrolytes

Secretin stimulates secretion of HCO3 and water

Question 14

What is the bile-dependent fraction of biliary secretion?

Answer 14

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

Question 15

What are choleretics?

Answer 15

Potent stimulators of bile secretion

Bile salts and acids act at choleretics

Question 16

What are the functions of the gallbladder?

Answer 16

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

Question 17

What are the two types of gallstones?

Answer 17

Cholesterol and Pigment stones

Question 18

What are cholesterol gallstones?

Answer 18

Most gallstones in western society

Cholesterol crystallized because of supersaturation, act as nucleus for stone formation

Question 19

What are pigment gallstones?

Answer 19

Composed of calcium bilirubinate

Bilirubin becomes unconjugated, which is now insoluble in bile

Precipitates with Ca to begin stone-forming process

Question 20

What is a cholecystectomy?

Answer 20

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