Final answer:
Bruises turn greenish in color due to the metabolic process of heme being broken down into biliverdin by the enzyme heme oxygenase in splenic macrophages.
Step-by-step explanation:
The reason behind bruises turning greenish in color is related to the metabolic activity of splenic macrophages when they process the heme from damaged red blood cells (RBCs). The enzyme heme oxygenase metabolizes heme to biliverdin, a green bile pigment. As a bruise heals, this causes the initially reddish-purple color to transition through various hues, including green.
Subsequent metabolic processes convert biliverdin into bilirubin, which is then transported to the liver. There, bilirubin is conjugated and excreted in bile, playing a significant role in the digestion of fats. When red blood cells are damaged due to injury, the breakdown of their hemoglobin leads to the release of these pigments, accounting for the colorful display that a bruise presents during the healing process.
This is part of the body's process of clearing away damaged red blood cells and their components. The color changes in a bruise reflect the stages of healing and the breakdown products involved.