GI Physiology: Bile

Question 1

What do bile duct cells do?

Answer 1

Secrete bicarbonate and fluid

Question 2

What are the major components of bile (4)?

Answer 2

Bile acids (major), phospholipids, cholesterol, bile pigments.

Question 3

What is the body’s major route of cholesterol elimination?

Answer 3

In bile

Question 4

How does bilirubin (product of RBC breakdown) get to the liver? What happens after that?

Answer 4

It attaches to albumin to go to the liver. Then, it is conjugated and goes into feces, or gets back in to the circulation and goes to the kidneys for excretion in urine.

Question 5

What is the primary function of bile salts?

Answer 5

To emulsify fats in the GI tract –> smaller TAG droplets.

Small TAG droplets + lipase –> FFAs + MAGs –> micelles

Question 6

Are bile salts amphiphatic?

Answer 6

Yeah

Question 7

Describe the pathways of bile salt synthesis.

Answer 7

In liver: cholesterol –> cholic acid (primary bile acid) –> GI lumen modification by bacteria –> deoxycholic acid (secondary bile salt) –> conjugation with glycine.

In liver: cholesterol –> chenodeoxycholic acid (primary bile acid) –> GI lumen modification by bacteria –> lithocholic acid (secondary bile salt) –> conjugation with taurine.

Question 8

Are bile acids detergents?

Answer 8

Yeah

Question 9

What are the five major components of micelles? What role do they play in absorption?

Answer 9

From liver: bile acids and phospholipids.

From food: 2-MAGs, FFAs, cholesterol

Micelles allow for a greater rate of FFA diffusion to the epithelium of the GI tract.

Question 10

What is the shape of a micelle?

Answer 10

Sphere

Question 11

How does the body re-use bile salts? How much is lost per day?

Answer 11

They are taken back in the distal ileum and get back to the liver via the hepatic portal vein. Only 15-30% of the bile salts are lost per day to excretion.

Question 12

By which two cellular mechanisms are bile salts taken up in the distal ileum?

Answer 12

1. Diffusion (they can cross the cell membrane because they are hydrophobic).
2. Na+-dependent symporter

Question 13

Between meals, the sphincter of Oddi is _______ (open or closed), causing bile to be stored in the __________.

Answer 13

closed; storage in gallbladder

Question 14

Eating stimulates gallbladder contraction and sphincter of Oddi relaxation by two mechanisms. What are they?

Answer 14

CCK and neural stimulation.

Question 15

Why is the concentration of bile in the gallbladder advantageous?

Answer 15

It helps micelles form (in biochem we learned that there is a threshold concentration required for micelle formation)

Question 16

Does the gallbladder actively pump water out of bile to concentrate it?

Answer 16

No, it pumps all sorts of ions out, and water passively follows!

Question 17

What is a cholangiocyte? What do they do?

Answer 17

Epithelial cells of the bile duct. They secrete bicarbonate rich fluid using a HCO3-/Cl- exchanger. Know the exchanger.

Question 18

What are gallstones made out of mostly?

Answer 18

Cholesterol mostly, some bile pigments

Question 19

Crystal formation is a key step in the formation of gallstones, which happens most often in the _______ layer within the gallbladder.

Answer 19

mucus

Question 20

Are gallstones in the gallbladder problematic?

Answer 20

Nope

Question 21

When are gallstones problematic?

Answer 21

When they get into the common bile duct. That needs fixing.