Answer: Each air sac is surrounded by a network of fine blood vessels (capillaries). The oxygen in inhaled air passes across the thin lining of the air sacs and into the blood vessels. This is known as diffusion. The oxygen in the blood is then carried around the body in the bloodstream, reaching every cell.
In my own words
Each air sac is encircled by an organization of fine veins (vessels). The oxygen in breathed in air goes over the slim coating of the air sacs and into the veins. This is known as dissemination. The oxygen in the blood is then hefted around the body in the circulation system, arriving at each cell.
