Pulmonary respiration is defined as the:

• A. Exchange of oxygen and carbon dioxide between alveoli and capillaries
• B. Exchange of gases between cells and circulating blood
• C. Exchange of oxygen in the bloodstream from the lungs to tissues
• D. Breathing rate and rhythm generated by the brain

Answer: (A)

Pulmonary respiration is the gas exchange that happens between the air in the alveoli and the blood in the pulmonary capillaries. Oxygen moves from the alveolar air into the blood, while carbon dioxide moves from the blood into the alveolar air to be exhaled. This exchange occurs across the alveolar–capillary membrane and is driven by differences in partial pressures, making it the lung-specific step of respiration. The other descriptions refer to gas exchange at the tissues or to the brain-driven mechanics of breathing, not the actual alveolar-to-blood exchange.