Multiple Choice
Which substance is primarily responsible for transporting oxygen in the blood?
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17. The Blood
Erythrocytes: Hemoglobin
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How does carbon monoxide (CO) exposure from smoking most directly affect a smoker’s blood oxygen-carrying capacity?
A
CO primarily binds to the iron in myoglobin in skeletal muscle, leaving hemoglobin function largely unchanged.
B
CO dissolves in plasma and is transported mainly as bicarbonate, which increases blood pH and improves oxygen unloading.
C
CO binds hemoglobin with very high affinity, forming carboxyhemoglobin and reducing oxygen delivery to tissues.
D
CO increases hemoglobin’s ability to bind oxygen, raising arterial oxygen content above normal.
Verified step by step guidance1
Step 1: Understand the role of hemoglobin in oxygen transport. Hemoglobin is a protein in red blood cells that binds oxygen molecules in the lungs and carries them to tissues throughout the body.
Step 2: Recognize that carbon monoxide (CO) has a much higher affinity for hemoglobin than oxygen does. This means CO competes with oxygen to bind to the iron in hemoglobin's heme groups.
Step 3: When CO binds to hemoglobin, it forms carboxyhemoglobin (HbCO), which prevents hemoglobin from carrying oxygen. This reduces the overall oxygen-carrying capacity of the blood.
Step 4: Understand that the presence of carboxyhemoglobin also shifts the oxygen-hemoglobin dissociation curve to the left, meaning hemoglobin holds onto oxygen more tightly and releases less oxygen to the tissues.
Step 5: Conclude that CO exposure from smoking most directly decreases oxygen delivery to tissues by forming carboxyhemoglobin, thereby reducing the amount of oxygen that hemoglobin can transport.
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