Transport of Bilirubin

Transport of Bilirubin

Q. 1 Bilirubin is absent in urine because it is :

 A

Distributed in the body fat

 B

Conjugated with glucoronide

 C

Not filterable

 D

Lipophilic.

Q. 1

Bilirubin is absent in urine because it is :

 A

Distributed in the body fat

 B

Conjugated with glucoronide

 C

Not filterable

 D

Lipophilic.

Ans. D

Explanation:

Unconjugated serum bilirubin is always bound to albumin, is not filtered by the kidney (not found in the urine)
In biliary obstruction or hepatocellular diseases, both conjugated and unconjugated bilirubin accumulate in plasma.
In hemolytic jaundice, total plasma bilirubin increases, but the proportion of the unconjugated and conjugated fractions remains unchanged.


Q. 2

Bilirubin is secreted by:

 A

Bile Salts

 B

Bile pigments

 C

Secretin

 D

CCK.

Q. 2

Bilirubin is secreted by:

 A

Bile Salts

 B

Bile pigments

 C

Secretin

 D

CCK.

Ans. A

Explanation:

A i.e. Bile salts

Substances that increase the secretion of bile are called as cholerecticsQ. Bile salts are amongst the most important physiological cholerectionQ


Q. 3 Bilirubin is the degradation product of –

 A

Albumin

 B

Globulin

 C

Heme

 D

Transferrin

Q. 3

Bilirubin is the degradation product of –

 A

Albumin

 B

Globulin

 C

Heme

 D

Transferrin

Ans. C

Explanation:

Ans. is ‘c’ i.e., Heme

Bilirubin metabolism

o Bilirubin is the end product of heme degradation.

o The heme is derived from –

(i)       Senescent erythrocytes by mononuclear phagocytic system in the spleen, liver and bone marrow (major source).

(ii)     Turnover of hemoproteins (e.g. cytochrome p.450).

o Heme is oxidized to biliverdin by heme oxygenase.

o Biliverdin is then reduced to bilirubin by biliverdin reductase.

o Bilirubin is transported to liver in bound form with albumin.

o There is carrier mediated uptake of bilirubin in the liver.

o This bilirubin is conjugated with glucuronic acid by UDP glucuronyl transferase (UGT1A1) to from conjugated bilirubin (bilirubin glucronides).

o Conjugated bilirubin is excreted into bile.

o Most of the conjugated bilirubin is deconjugated and degraded to urobilinogen.

o The most of the urobilinogen is excreted in the feces.

o Approximately 20% of the urobilinogen is reabsorbed in the ileum and colon and is returned to the liver, and promptly rexcreted into bile —> Enterohepatic circulation.

o The small amount that escapes this enterohepatic circulation is excreted in urine.

Quiz In Between


Q. 4 Bilirubin is absent in urine because it is‑

 A

Distributed in the body fat

 B

Conjugated with glucoron

 C

Not filtered

 D

None

Q. 4

Bilirubin is absent in urine because it is‑

 A

Distributed in the body fat

 B

Conjugated with glucoron

 C

Not filtered

 D

None

Ans. C

Explanation:

Answer is C (Not filtered)

Normal urine does not contain bilirubin because normal blood contains bilirubin in the uncongugated form. Unconjugated bilirubin is lipid soluble or lipophilic (water insoluble) because it is transported in the blood as a complex with albumin (albumin-bilirubin complex) which is not allowed to filter through the glomerulus.

Although conjugated bilirubin is water soluble and filterable at the glomurulus, conjugated bilirubin is not present in the blood normally and hence does not filter to appear in the urine.

Unconjugated bilirubin present in blood is complexed with albumin to make it soluble in blood and transport it to the liver. However, the glomerulus does not allow the albumin bilirubin complex to filter and hence bilirubin does not appear in urine.

Conjugated bilirubin is formed in the liver and directly excreted into the GIT through bile where it is reduced to urobilinogen and stercobilinogen. Conjugated bilirubin does not normally circulate in the blood at all and hence despite being filterable and water soluble it does not appear in urine.


Q. 5

Urobilinogen is formed in the:   
September 2006

 A

Liver

 B

Kidney

 C

Intestine

 D

Spleen

Q. 5

Urobilinogen is formed in the:   
September 2006

 A

Liver

 B

Kidney

 C

Intestine

 D

Spleen

Ans. C

Explanation:

Ans. C: Intestine

Urobilinogen is a colourless product of bilirubin reduction. It is formed in the intestines by bacterial action. Some urobilinogen is reabsorbed, taken up into the circulation and excreted by the kidney. This constitutes the normal “enterohepatic urobilinogen cycle”.

Urobilinogen content is determined by a reaction with Ehrlich’s reagent, which contains para-Dimethyl amino benzaldehyde and may be measured in Ehrlich units

Quiz In Between


Q. 6 Bilirubin bound inside hepatocyte to ‑

 A

Albumin

 B

Ubiquinone

 C

Ligandin

 D

Globulin

Q. 6

Bilirubin bound inside hepatocyte to ‑

 A

Albumin

 B

Ubiquinone

 C

Ligandin

 D

Globulin

Ans. C

Explanation:

Ans. is ‘c’ i.e., Ligandin

Bilirubin metabolism

Bilirubin is the end product of heme degradation.

The heme is derived from –

i) Senescent erythrocytes by mononuclear phagocytic system in the spleen, liver and bone marrow (major source).

ii) Turnover of hemoproteins (e.g. cytochrome p.450).

Heme is oxidized to biliverdin by heme oxygenase.

Biliverdin is then reduced to bilirubin by biliverdin reductase.

Bilirubin is transported to liver in bound form with albumin.

Bilirubin is transferred to hepatocytes where it is bound to ligandin.

There is carrier mediated uptake of bilirubin in the liver.

This bilirubin is conjugated with glucuronic acid by UDP glucuronyl transferase (UGT1A1) to from conjugated bilirubin (bilirubin glucronides).

Conjugated bilirubin is excreted into bile.

Most of the conjugated bilirubin is deconjugated and degraded to urobilinogen.

The most of the urobilinogen is excreted in the feces.


Q. 7 All are involved in bilirubin metabolism except‑

 A

ALA synthase

 B

Heme oxygenase

 C

Biliverdine reductase

 D

Glucuronyl transferase

Q. 7

All are involved in bilirubin metabolism except‑

 A

ALA synthase

 B

Heme oxygenase

 C

Biliverdine reductase

 D

Glucuronyl transferase

Ans. A

Explanation:

Ans. is ‘a’ i.e., ALA synthase 

Quiz In Between



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