Organs can appear yellow primarily due to the presence of bilirubin.
Bilirubin is a yellow-red pigment that's a byproduct of the normal breakdown of heme, a component of red blood cells. Here's a more detailed breakdown:
- Bilirubin Production: When red blood cells break down, heme is converted into bilirubin.
- Liver's Role: The liver processes bilirubin. It takes up bilirubin from the blood, conjugates it (making it water-soluble), and secretes it into bile. This bilirubin gives the liver a yellowish-red tint.
- Gallbladder and Biliary Ducts: Bilirubin also affects the gallbladder and biliary ducts, tinting their epithelia yellowish-red.
- Intestinal Transformation: Once bilirubin enters the small intestine via bile, bacteria metabolize it into urobilinogen and stercobilinogen. These are eventually excreted in urine and feces, respectively, contributing to their color.
Therefore, the presence and processing of bilirubin are the main reasons certain organs, like the liver, gallbladder, and biliary ducts, can appear yellow.
