Hematology: Normocytic Anemia

Hemoglobin Breakdown: Bilirubin metabolism begins in the reticuloendothelial system, primarily in the spleen and the liver. Here, old or damaged red blood cells are broken down, and their hemoglobin is released. Heme Conversion: Heme is enzymatically converted into a molecule called biliverdin, which is green in color. This conversion is catalyzed by an enzyme known as heme oxygenase. Biliverdin to Bilirubin: Biliverdin is then converted into unconjugated bilirubin, a yellow compound. This conversion is also enzymatic and is carried out by biliverdin reductase. Binding to Albumin: Unconjugated bilirubin is not water-soluble and must bind to a carrier protein, primarily albumin, for transport through the bloodstream to the liver. Liver Uptake: In the liver, unconjugated bilirubin is taken up by hepatocytes (liver cells). Inside the liver, it is conjugated with glucuronic acid, a water-soluble substance, through a process called glucuronidation. This converts unconjugated bilirubin into conjugated bilirubin (also known as direct bilirubin). Secretion into Bile: Conjugated bilirubin is then secreted into bile, a greenish-brown fluid produced by the liver and stored in the gallbladder. Conjugated bilirubin gives bile its characteristic color. Biliary Excretion: When the gallbladder contracts in response to a meal, bile is released into the small intestine, where it helps digest fats. Conjugated bilirubin, along with other substances in bile, is excreted into the intestines. Intestinal Metabolism: In the intestines, bacteria act on conjugated bilirubin, breaking it down further. This process forms urobilinogens, some of which are reabsorbed into the bloodstream and excreted by the kidneys, giving urine its characteristic yellow color. The remaining urobilinogens are converted into stercobilin, which contributes to the brown color of feces. Excretion: Finally, the majority of urobilinogens are excreted in feces, which are brown due to the presence of stercobilin. Small amounts of bilirubin may be excreted in urine, giving it a yellow color.

Unconjugated bilirubin - causes yellow color