AP BIOLOGY

Detailed explanation-1: -The walls of the alveoli share a membrane with the capillaries. That’s how close they are. This lets oxygen and carbon dioxide diffuse, or move freely, between the respiratory system and the bloodstream. Oxygen molecules attach to red blood cells, which travel back to the heart.

Detailed explanation-2: -At the very end of the air passages are clusters of small air filled sacs called alveoli (singular: alveolus). These air sacs are surrounded by tiny blood vessels called capillaries (Image 1).

Detailed explanation-3: -Alveoli are thin walled and surrounded by blood capillaries for ease of gas exchange via diffusion.

Detailed explanation-4: -There are ∼ 300 million alveoli and 1, 000 capillaries per alveolus. The enormous number of capillaries associated with the numerous alveoli provides an immense surface area for respiration.

Detailed explanation-5: -The pulmonary capillary networks surround the alveoli and form single layer plexuses that reside in the interalveolar septa.