Hemoglobin is a protein in the blood that contains iron, and its basic function is the transfer of oxygen from the lungs to the tissues. Same way oxygen is transferred to the muscles, too. Hemoglobin is made up of four globin subunits, each of which contains a heme molecule, to which an oxygen molecule can bind.
Hemoglobin is found in the red blood cells of all vertebrates, including humans. In addition to oxygen, hemoglobin also transports carbon dioxide, so we distinguish between:
⦁ oxyhemoglobin – hemoglobin that transports oxygen and gives the blood a bright red color,
⦁ carbaminohemoglobin – hemoglobin that transports carbon dioxide and gives the blood a dark purple color.
Oxygen is transported from the lungs to the tissues via the arteries, whose blood is rich in oxygen and therefore has a bright red color and returns from the tissues to the lungs via the veins, which are poor in oxygen and therefore the venous blood is dark purple in color.