How does oxygen get into the blood from these air sacs?

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.

Diffusion

Explanation:

Epithelial tissue makes it perfect for the exchange between oxygen (from the lungs to the blood) and CO2 (from the blood to the lungs).

There is a higher amount of oxygen in the lungs than the deoxyganeted blood in the pulmonary vein. This means that oxygen will readily be exchanged between the two.