Gas exchange in the lungs takes place between the blood in the capillary network surrounding the alveoli, and the air in the alveoli itself. All of the blood from the right ventricle flows through the pulmonary artery to the capillary network which surrounds the alveoli.as exchange between the air within the alveoli and the pulmonary capillaries occurs by diffusion. The oxygen must first dissolve before passing through the respiratory epithelium.