How does carbon monoxide affect oxygen transport in the body?

• A. It binds more strongly to hemoglobin, reducing oxygen delivery
• B. It increases red blood cell production
• C. It blocks oxygen from binding to tissues directly
• D. It has no effect on oxygen transport

Answer: (A)

Carbon monoxide disrupts oxygen transport by binding to hemoglobin with a much higher affinity than oxygen, forming carboxyhemoglobin. This directly reduces the amount of oxygen that blood can carry because most hemoglobin sites are occupied by CO and cannot bind O2. In addition, the CO bound to hemoglobin shifts the oxygen dissociation curve to the left, meaning the remaining oxygen-bound hemoglobin holds onto oxygen more tightly and is less willing to release it to tissues. So, even if oxygen is present in the lungs, delivery to tissues is impaired, leading to tissue hypoxia. The other ideas—increasing red cell production or blocking O2 from binding to tissues directly—don’t explain the primary transport problem, which is CO’s high-affinity binding to hemoglobin and the consequent reduced oxygen delivery and unloading.