The figure shown above shows a simple diagram of gas exchange occurring in the alveolus. If gas A goes “out” and gas B goes “ in” with respect to the blood as shown in the diagram, identify gases A and B.
A –carbon dioxide, B- oxygen
∙ The alveoli are thin walled structures that are richly supplied with blood capillaries to facilitate the exchange of gases between blood and air filled lungs.
∙ Oxygen is absorbed by the RBC’s present in the blood (blood capillaries) from alveoli. RBC’s contain haemoglobin that combines with oxygen to form oxyhaemoglobin. Thus, oxygen is transported to all parts of the body by arteries.
∙ The carbon-dioxide formed in the tissues is transported to the lungs by the blood (in the veins) as dissolved in plasma and by RBC’s as carbamino-haemoglobin.
∙ Hence, the gas that moves out of alveoli into the bloodstream is oxygen and the one that moves from the blood vessel to the alveoli is carbon-dioxide.