Biochemistry of Bile

Question 1

Composition of human Bile

Answer 1

Bile acid (salt) 80%

Phosholipids 16% (most are phosphotydylcholine)

Cholesterol (4%)

Minor constituents (bile pogments, proteins, electrolytes drugs)

Question 2

Bile salts are synthesized from ____

Answer 2

cholesterol

Question 3

Rate limiting and regulated step in bile acid synthesis

Answer 3

7a-hydroxylase

Hydroxyl group adde d to the 7 position

lots of bile around - enzyme less active
not a lot of bile around - less active

Question 4

7a-Hydroxylase requires which cofactors

Answer 4

NADPH
CYP7A
O2
Vitamin C (ascorbate)

Question 5

Which exzyme is required for formation of cholic acid and chendeoycholic acid

of these which is more prominent in humans

Answer 5

12a-hydroxylase

Cholic acid predominates

Question 6

12a-Hydroxylase requires which cofactors

Answer 6

NADPH
O2
CoA

Question 7

Cholic acid and chendeoxycholic acid are conjugated to what

Answer 7

taurine (sulfur containing group)
Glycine

** this forms the primary bile salts

Question 8

What are the primary bile salts

Answer 8

Tuarocholic acid
Glyocholic acid
Taurochendeoycholic acid
Glycochnendeoxychilic acid

Question 9

What are secondary bile salts? How are they formed

Answer 9

Deoxycholic acid and lithcholic acid

deconjugation by intestinal bacteria

Question 10

why isnt lithocholic acid absorbed in the ileum with the other bile salts

Answer 10

limited solubility

Question 11

Heme oxygenase

Answer 11

Heme is converted to biliverdin

Question 12

only endogenous source of CO production

Answer 12

Heme oxygenase conversion of heme to biliverdin

Question 13

biliverdin reductase

Answer 13

biliverdin –> bilirubin

Question 14

bilirubin is bound to ____ and transported to the liver through the blood

Answer 14

albumin

Question 15

diglucoroide

Answer 15

conjugated form of bilirubin made by the liver

Question 16

fate of diglucoriode in the colon

Answer 16

converted to urobiligen by intestinal bacteria

Question 17

fate of urobilogen

Answer 17

some gets oxygenated to form urobilin an d is secreted in the urine

some further metabolized to stercobolinogen which is oxidated to stercobilin

Question 18

what gives urine yellow color

Answer 18

urobilin

Question 19

what gives feces brown color

Answer 19

stercobilin

Question 20

Prehepatic jaundice id due to what?

Answer 20

due to production of bilirubin that excedes the livers capacity to conjugate it

ex: Hemolytic anemia

Question 21

Increased total bilirubin
Increased unconjugated bilirubin (indirect)
Relatively normal stool color

Answer 21

Prehepatic jaundice

Question 22

Hepatic jaundice is due to what?

Answer 22

failure of the liver to conjugate bilirubin

ex: hepatic disease

Question 23

Increased total bilirubin
Increased unconjugated bilirubin (indirect)
Clay colored stools

Answer 23

Hepatic Jaundice

Question 24

Post-hepatic jaundice is due to

Answer 24

due to regurgitation of conjugated bilirubin into the blood. Liver is handling the bile but the path is obstructed and it has nowhere to go so it enters the blood

Gallstones, obstruction

Question 25

Increased total bilirubin
increased conjugated bilirubin (direct)
Clay colored stools
dark brown pigmentation of urine

Answer 25

Post-hepatic jaundice

Question 26

Physiologic Jaundice

Answer 26

liver of neonates has limited capacity to conjugate bilirubin

active destruction of fetal blood cells with HbF to switch to adult blood cells HbA

Phototherapy

Question 27

How does phototherapy work in physiologic jaundice

Answer 27

making unconjugated bilirubin water soluble