Explain Bile pigments - Constituents of Bile

The red blood cells are broken down when they are old (life span of red blood cell is 120 days). They are taken up by the reticuloendothelial system. Haemoglobin is released and by degradation, opening of the porphyrin ring system occurs. The degraded compound is known as verdo haemoglobin. This is broken down to haem and globin. Globin is broken down to amino acids and enters the general amino acid pool of the body. Iron is stored in the body as apoferritin, haemosiderin which is re-utilized to form new haemoglobin. The rest of the haem is converted to yellow pigment called as bilirubin. Bilirubin is oxidised to green pigment biliverdin. The bilirubin then combines with plasma albumin. When it enters the liver cells, it is conjugated with glucuronic acid.

It is to be noted that bilirubin, present in blood (haemobilirubin) is not the same as the bilirubin present in bile (cholebilirubin). Haemobilirubin remains combined with serum albumin and cholebilirubin remains in combination with glucuronic acid.