bilirubiiniaineenvaihduntaa

Bilirubiiniaineenvaihduntaa refers to the metabolic process by which bilirubin is processed and eliminated from the body. Bilirubin is a yellow pigment produced during the normal breakdown of red blood cells. When red blood cells reach the end of their lifespan, typically around 120 days, they are broken down in the spleen, liver, and bone marrow. This breakdown releases heme, which is then converted into biliverdin, and subsequently into bilirubin.

Initially, bilirubin is unconjugated, meaning it is not soluble in water and is bound to albumin for transport in the bloodstream to the liver. In the liver, unconjugated bilirubin is taken up by liver cells and conjugated with glucuronic acid, a process known as glucuronidation. This makes bilirubin water-soluble, allowing it to be excreted from the body.

The conjugated bilirubin is then secreted into the bile, which is produced by the liver and stored in the gallbladder. Bile is released into the small intestine, where conjugated bilirubin is further metabolized by bacteria into urobilinogen. A portion of urobilinogen is reabsorbed into the bloodstream and excreted by the kidneys, giving urine its characteristic yellow color (as urobilin). The remaining urobilinogen is converted in the large intestine into stercobilin, which is responsible for the brown color of feces. Disruptions in any part of this metabolic pathway can lead to an accumulation of bilirubin in the blood, causing jaundice, a yellowing of the skin and whites of the eyes.