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Flashcards in Bile secretion Deck (7)
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1
Q

What is the composition of bile?

A

97% H20

  1. 7% bile salts
  2. 2% bile pigments
  3. 7% inorganic salts
  4. 06% cholesterol
  5. 2% phosphatidylcholine
  6. 15% FAs
  7. 1% TAGS

It is isosmotic, due to AQPs in the cholangiocytes.

Lipid composition is
10:3:1
Bile acids : Phosphatidyl Choline: Cholesterol

Ionic composition: Similar to plasma, but alkaline, but with lower Cl-, lower Na+, and higher HCO3- (up to 60mM), and with no glucose or a.a.s

Glucose and a.a.’s are absent, as these are all reclaimed by Na+ cotransporters in the cholangiocytes.

2
Q

What is the rate limiting step in bile acid formation?

A

7-alpha hydroxylation of cholesterol

3
Q

How are the components of bile transported into the bile canaliculi?

A

1) By active transport (ATP driven) transport of the Bile Sale Export Pumps.

Active pumping by BSEPs.

2) By active transport of conjugated bile salts by another exporter
3) By active transport of phospholipids by ABC transporter ATPases.
4) Chloride/Bicarbonate exchanger and the CFTR channel (increase HCO3- concentration in the bile ducutle, and the CL- is later reabsorped in the gall bladder)

4
Q

How much bile is secreted per day?

A

200-1200ml/day

continuously secreted by liver and then stored in gall bladder

5
Q

What induces bile release from the gall bladder?

A

Relaxation of the sphincter of Oddi and contraction of the gall bladder smooth muscle,
stimulated by Secretin released from the S-Cells of the duodenum.

6
Q

What happens to the bile as it is stored in the gall bladder? How is hepatic bile different from gall bladder bile?

A

Na+, Cl-, and H2O are all resorbed, concentrating the bile acids/bile salts, and the bile is made more acidic.

Cl- ions flow outward following the flow of water due to the active pumping of Na+ from the bile by two transporters:

1) a luminal Na+/H+ ATPase exchanger
2) the basolateral Na/K pumps.

The bile is also made more acidic while the Na+ is reclaimed by these Na+/H+ ATPase.

Hepatic bile:
10-20mM bile acid
7.8 - 8.6 pH

Gall bile:
50-200mM bile acid
7.0-7.4 pH

Both are isosmotic however.

7
Q

Where does nutrient absorption primarily take place in the GI tract?

Where does Bile Acid absorption primarily take place?

Where does Cobalamin absorption primarily take place?

A

Nutrients absorbed in the Duodenum

Bile Acids - ileum

Cobalamin (B12) - Only in the ileum