What is the first step in the process of oxygenation?

• A. Obtain oxygen from the air.
• B. Transport air through the respiratory tract to alveoli.
• C. Diffuse oxygen into blood to be carried to all cells of the body.
• D. Remove carbon dioxide from the body.

Answer: (A)

Bringing in air that contains oxygen is the starting point. Ventilation provides the oxygen source and creates the partial pressure gradient in the lungs that allows oxygen to diffuse into the blood. Without oxygen entering the alveoli, there’s no oxygen available for diffusion, transport, or tissue use. Once oxygen is present in the alveoli, it diffuses across the alveolar-capillary membrane into the blood, where it’s carried to all cells and used for metabolism. Carbon dioxide removal is part of the later exchange cycle, not the initial step.