How is bilirubin processed and excreted by the liver?

Bilirubin is processed by the liver through conjugation and excreted as bile into the small intestine.

Bilirubin is a yellowish substance produced by the breakdown of old red blood cells in the spleen. It is transported in the bloodstream to the liver, where it undergoes a process called conjugation. This process involves the addition of two molecules of glucuronic acid to the bilirubin molecule, making it water-soluble. This conjugated bilirubin is then secreted into the bile, a digestive fluid produced by the liver.

The bile, containing the conjugated bilirubin, is stored in the gallbladder and released into the small intestine during digestion. Here, the bilirubin is further metabolised by bacteria in the gut, transforming it into urobilinogen. Some of this urobilinogen is reabsorbed into the bloodstream and excreted by the kidneys in urine, giving it a yellow colour. The majority, however, remains in the gut and is converted into stercobilin, which is responsible for the brown colour of faeces.

The processing and excretion of bilirubin by the liver is a crucial part of the body's waste management system. It ensures the efficient removal of waste products from the breakdown of red blood cells, preventing their accumulation in the body, which can lead to jaundice. This process also highlights the liver's vital role in detoxification and waste removal, underlining its importance in maintaining overall health.