What is the oxygen affinity level of adult hemoglobin?

Adult hemoglobin, also known as hemoglobin A (HbA), has a low affinity for oxygen compared to fetal hemoglobin. This design enables effective oxygen release to tissues, particularly in the peripheral areas where it's most needed. The physiological adaptation of having a lower oxygen affinity allows adult hemoglobin to efficiently release oxygen during periods of moderate to high exercise or in conditions where tissues are metabolically active and consuming more oxygen.

In contrast, fetal hemoglobin has a higher affinity for oxygen, which is crucial as it must extract oxygen from the mother’s bloodstream in the placenta. Overall, the oxygen affinity level of adult hemoglobin being low enables optimal oxygen delivery when coupled with the physiological conditions of the human body, such as changes in pH and carbon dioxide levels, which further influence oxygen binding and release.