Diffusion due to differences in air pressures.
"alveoli"
gas exchange occurs between pulmonary capillaries and the alveoli in the lungs.
The membrane of the alveolus, the air sacs in the lungs where this process takes place, is only one cell thick. The wall of the capillary running adjacent to the alveolus is also one cell thick, so the gases are exchanged between the alveolus and the capillary cell membranes.
easy efficient exchange between air and blood
Around the lungs,the blood is separated from the air inside each alveolus by only two cell layers; the cells making up the wall of the alveolus and the capillary wall itself. This is a distance of less than a thousandth of a millimetre. Because the air in the alveolus has a higer concentration of oxygen than the blood entering the capillary network, oxygen diffuses from the air across the wall of the alveolus and into the blood. That is why the distance is important.
alveolus
Oxygen passes from the air sacs in the lungs to the blood in the capillaries, carbon dioxide passes the other way.
The site of respiration is the cells, more specifically, the mitochondria
An alveolus (plural: alveoli, from Latin alveolus, "little cavity") is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the dead ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well.
Capillary Exchange is a biological term. This is where fluids, gasses, nutrients, and wastes are exchanged between the blood and body tissues by diffusion.
Pulmonary circulation is the exchange of blood between the heart and the lungs. Systemic circulation is the the exchange of blood between the heart and the body overall
Capillary system is where gas exchange occurs
gas exchange