What is the role of hemoglobin in gas exchange?

Hemoglobin transports oxygen from the lungs to the tissues of the body. Hemoglobin is the iron-containing protein within red blood cells that binds oxygen reversibly. In the pulmonary capillaries, where the partial pressure of oxygen is high, hemoglobin binds up to four oxygen molecules, forming oxyhemoglobin. As red blood cells circulate to peripheral tissues where oxygen tension is lower and carbon dioxide levels are higher, hemoglobin releases its oxygen for cellular use. Hemoglobin also assists in the transport of carbon dioxide back to the lungs, primarily through carbaminohemoglobin formation and by contributing to the buffering system that facilitates carbon dioxide carriage as bicarbonate. Hemoglobin does not produce oxygen; oxygen is derived from inspired air and arrives at the alveoli through ventilation. Hemoglobin does not store oxygen in the lungs as a reserve supply; it binds and releases oxygen dynamically according to partial pressure gradients. Hemoglobin does not prevent carbon dioxide from entering the bloodstream; carbon dioxide freely diffuses from tissues into blood and is transported in multiple forms, with hemoglobin playing only a minor direct role in that carriage. Therefore, the primary and most accurate description of hemoglobin's role in gas exchange is its function as an oxygen carrier from the lungs to the body's tissues.