Final answer:
Heme is converted to bilirubin in the liver, where it is part of the breakdown of hemoglobin from red blood cells. It is then secreted into the bile, processed in the intestines, and excreted in feces.
Step-by-step explanation:
Heme is converted to bilirubin in the liver. The non-iron portion of heme is degraded into biliverdin, a green pigment, and then reduced to bilirubin, a yellow pigment. This process is part of the breakdown of hemoglobin from old or damaged red blood cells which are removed from circulation by the spleen and transported to the liver via the hepatic portal system. Once in the liver, bilirubin is bound to albumin, secreted into the bile, and then sent to the intestines. In the intestines, bacteria convert bilirubin to urobilinogen and then into stercobilin, which is excreted in feces, giving stool its characteristic brown color. Broad-spectrum antibiotics can disrupt this process by eliminating the bacteria responsible for breaking down bilirubin.