Capillaries vs. Alveoli: Understanding Oxygen and Nutrient Delivery

Alveoli are to the lungs what capillaries are to body tissues.

• Alveoli – tiny air sacs; site of O₂/CO₂ exchange between air and blood.
• Capillaries – smallest blood vessels; site of O₂/nutrient delivery and waste removal between blood and tissues.

Both are thin-walled (single endothelial layer), highly branched networks maximizing surface area for diffusion. The alveolar-capillary unit is the functional interface of respiration.