The oxygen–hemoglobin dissociation curve describes the percent oxygen saturation of hemoglobin as a function of the partial pressure of oxygen (PO2) in the surrounding fluid. As the PO2 increases on the horizontal axis, the oxygen saturation percentage also increases on the vertical axis. In comparison to that of adult hemoglobin, how is the fetal oxygen–hemoglobin dissociation curve shifted?

a. to the left of the adult curve, indicating a lower oxygen affinity of fetal hemoglobin
b. to the left of the adult curve, indicating a higher oxygen affinity of fetal hemoglobin
c. to the right of the adult curve, indicating a lower oxygen affinity of fetal hemoglobin
d. to the right of the adult curve, indicating a higher oxygen affinity of fetal hemoglobin

b. to the left of the adult curve, indicating a higher oxygen affinity of fetal hemoglobin

Explanation:

The oxygen–hemoglobin dissociation curve describes how our blood transfers oxygen. The oxygen–hemoglobin dissociation curve is decided by hemoglobin affinity for oxygen and relates oxygen saturation and partial pressure of oxygen (PO2) in the surrounding fluid.

Hemoglobin saturation is indicated by the totall hemoglobin bound to oxygen vs. the capacity of hemoglobin to carry oxygen. Oxygen is bound to hemoglobin according to partial pressure of concerned oxygen. Like in lungs the partial pressure of oxygen is greater and oxygen immediately bound to hemoglobin. While in body tissue the partial pressure of oxygen is less and oxygen is released by hemoglobin.

The oxygen saturation percentage increases on the vertical axis in response to increase in PO2 on the horizontal axis the oxygen–hemoglobin dissociation curve of adults. The fetal blood has higher affinity for oxygen than adults. So, at a given partial pressure of oxygen the oxygen will tend to go from maternal blood to fetal blood. That why in comparison to adults the fetal oxygen–hemoglobin dissociation curve shifts to the left of the adult curve, indicating a higher oxygen affinity of fetal hemoglobin.