Advanced Patient Assessment Practice Exam

The substance that is a vital constituent of the heme portion of hemoglobin is iron. Hemoglobin, which is essential for transporting oxygen in the blood, contains four heme groups, and each heme group includes an iron atom at its center. This iron is crucial because it has the ability to bind to oxygen molecules, allowing hemoglobin to pick up oxygen in the lungs and release it in tissues where it is needed. Without iron, the heme cannot function properly, leading to decreased oxygen-carrying capacity and potential conditions like anemia.

The other substances listed do not play a role in the structure of heme; protein is a component of the overall hemoglobin molecule but not of the heme itself. Calcium and sodium are important for various functions in the body, but they do not have any direct role in the formation or function of hemoglobin's heme group.