Step I FA 2012 Pg. 350

[kaleerkalut]

It states that bilirubin undergoes enterohepatic cycling. I was under the impression that ONLY bile acids undergo enterhepatic cycling because bilirubin is a waste product. Can anybody elaborate on this? Thanks 🙂

 

[Phlame217]

Bilirubin is resorbed along with bile salts and excreted in urine, hence giving urine its typically yellow color.

In short:

RBC Breakdown = Unconjugated bilirubin (binds to albumin)
Liver takes it up, conjugates it = Conjugated bilirubin (water soluble)
Liver secretes to bile, bile dumps in intestines = CB in intestines
Bacteria in intestines convert 80% into Urobilinogen which spontaneously converts to urobilin (brown pigment of feces).
20% of CB is resorbed with the bile acid circulation.
90% of that is picked up by the liver for the enter hepatic cycling.
10% is filtered by kidneys in the form of urobilin giving it its yellow color.

So recap numbers
Say you have 100 grams of UCB
Liver converts it to 100 grams of CB
100 grams excreted in bile acids into intestines.
80 Grams pooped out after changing to urobilin

20 grams resorbed with bile acids
18 grams re-filtered by liver
2 grams peed out.

 

[loveoforganic]

RBC Breakdown = Unconjugated bilirubin (binds to albumin)
Liver takes it up, conjugates it = Conjugated bilirubin (water soluble)
Liver secretes to bile, bile dumps in intestines = CB in intestines
Bacteria in intestines convert 80% into Urobilinogen which spontaneously converts to urobilin (brown pigment of feces).
20% of CB is resorbed with the bile acid circulation.
90% of that is picked up by the liver for the enter hepatic cycling.
10% is filtered by kidneys in the form of urobilin giving it its yellow color.

Tiny correction (probably just a typo) - bolded should be stercobilin

 

[kaleerkalut]

Bilirubin is resorbed along with bile salts and excreted in urine, hence giving urine its typically yellow color.

In short:

RBC Breakdown = Unconjugated bilirubin (binds to albumin)
Liver takes it up, conjugates it = Conjugated bilirubin (water soluble)
Liver secretes to bile, bile dumps in intestines = CB in intestines
Bacteria in intestines convert 80% into Urobilinogen which spontaneously converts to urobilin (brown pigment of feces).
20% of CB is resorbed with the bile acid circulation.
90% of that is picked up by the liver for the enter hepatic cycling.
10% is filtered by kidneys in the form of urobilin giving it its yellow color.

So recap numbers
Say you have 100 grams of UCB
Liver converts it to 100 grams of CB
100 grams excreted in bile acids into intestines.
80 Grams pooped out after changing to urobilin

20 grams resorbed with bile acids
18 grams re-filtered by liver
2 grams peed out.

Thanks!

 

[Morsetlis]

This website teaches it pretty well if you need more elaboration:

http://olddoc.tmu.edu.tw/chiaungo/profes/bilirubin.htm