Heme & PorphyrinDorland’s Medical Dictionary for Health Consumers, 2007, informs us heme is “an iron compound of protoporphyrin which constitutes the pigment portion or protein-free part of the hemoglobin molecule.” Heme is the colorful portion (red) of our blood. Notice, in particular, the partial word in the definition, porphyrin.
Recycling & TrashRed blood cells become old and need to be replaced. What happens to the old red blood cells? They are, first, consumed by macrophages in the blood. For the person who has his or her body intact, much of this occurs within the spleen. It also occurs in other parts of the body. It should be noted that most of the iron is extracted for reuse, and does not remain in any product that is excreted.
The Spleen & BileHeme contains four pyrrole-like, nitrogen-containing rings, connected together into a porphyrin ring (recall the reference above). The heme portion is converted into bilirubin—an open structure containing these rings. This metabolism usually occurs within the spleen, and so the bilirubin is part of what is called “bile.”
The Final Act – Bilirubin Yields UrineBilirubin is further broken down into “urobilins.” The process involves the liver. A small amount of this lightly tinted waste is passed out in the urine, and this is why we identify its color as urine yellow.
So now you know. And guess what? You are transparent. Which means, I can read your mind. You are wondering why feces are brown. Am I right or am I right?
References: ← Back to Classic Science