alleryStart learning →The non-iron portion of heme is degraded into which sequence of pigments?
ABilirubin first, then biliverdin
BStercobilin first, then bilirubin
CBiliverdin first, then bilirubin
DUrobilinogen first, then biliverdin
Answer & Solution
Correct answer: C. Biliverdin first, then bilirubin
1. When a macrophage breaks down hemoglobin, the globin goes to amino acids and the iron goes to storage or transport.
2. What is left is the non-iron portion of heme.
3. It is degraded first into biliverdin, a green pigment.
4. Biliverdin is then converted into bilirubin, a yellow pigment.
5. The order is visible clinically: a fresh bruise shows the green of biliverdin before the yellow of bilirubin.
6. Urobilinogen and stercobilin come later still, after gut bacteria act on bilirubin, so any option placing them first reverses the whole pathway.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 18 "The Cardiovascular System: Blood", section 18.3 Erythrocytes_
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