God made it that way and it doesn't need to be described as it is God's will
Exchange of carbon-di-oxide for oxygen takes place between capillaries and tissues.The exchange of gases occur through diffusion.In Lungs, oxygen from inhaled air in the alveolar space moves into the RBCs in the capillaries and the carbon-di-oxide moves form the RBCs in the capillaries to the alveolar space which is exhaled during respiration.In other tissues, the Oxygen is given to the tissues and carbon-di-oxide is taken from the tissues into the blood.Many gases can be exchanged across the capillaries but the exchange of oxygen and carbon-di-oxide occurs normally in the body.
as it moves through blood vessels capillaries in the alveoli walls, your blood takes oxygen from the alveoli and gives off carbon dioxide to the alveoli
In the lungs, in the alveolar capillaries
Capillaries exchange food, oxygen, and carbon dioxide.
Within the lungs.
they exchange in the aveoli and capillaries
Blood releases carbon dioxide and acquires oxygen, in the lungs. The opposite exchange takes place throughout the body on a cellular level, as each cell consumes oxygen from the blood and releases carbon dioxide into the blood.
Oxygen passes from the air sacs in the lungs to the blood in the capillaries, carbon dioxide passes the other way.
Capillaries
Unlike mammals who absorb oxygen through the alveolar in their lungs, frogs are able to use their skin as a surface for gas exchange. The capillaries carry oxygen poor blood underneath the skin so that the oxygen in the air or water will be transported into the blood.
Capillaries are the smallest blood vessels in your body and act as the exchange point for oxygen.
exchange of oxygen and carbon dioxide takes place in the capillaries