how does gas exchange occur in the lungs and in body tissues?
in the lungs, oxygen diffuses from the air in alveoli into the blood of surrounding capillaries. most of the oxygen enters red blood cells and combines with the heme portions of hemoglobin to form oxyhemoglobin. about 97% of the oxygen is tansposted as oxyhemoglobin. only 3% is dissolved in the plasma.
in body tissuees, oxyhemoglobin releases oxygen, and it diffuses from capillary blood into the tissue cells. actually, only about 25% of the oxygen is released, so oxyhenoglobin is present even in deoxygenated blood.