Which of the following is responsible for the movement of O2 from the alveoli into the blood in the pulmonary capillaries?: (A) Active transport, (B) Filtration, (C) Facilitated diffusion, (D) Passive diffusion
Answer is D. Gases diffuse from the alveoli to the blood in the pulmonary capillaries or vice versa across the thin alveolocapillary membrane made up of the pulmonary epithelium, the capillary endothelium, and their fused basement membranes.