As a subject matter expert in respiratory physiology, I can tell you that the blood picks up oxygen in the lungs. Specifically, oxygen enters the bloodstream through the process of gas exchange which occurs across the walls of the alveoli, tiny air sacs in the lungs. Here's a step-by-step breakdown of the process:


1. Inhalation: When you breathe in, air containing oxygen is drawn into the lungs.

2. Diffusion: Oxygen in the air within the alveoli diffuses across the thin walls of the alveoli and the surrounding capillaries.

3. Binding to Hemoglobin: Once in the bloodstream, oxygen molecules bind to hemoglobin, a protein in red blood cells that transports oxygen.

4. Transportation: Oxygen-rich blood is then transported from the lungs to the heart, which pumps it throughout the body to cells and tissues.

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Red blood cells pick up oxygen in the lungs. Blood travels away from the heart and lungs through the arteries (ar-tuh-reez). Red blood cells drop off oxygen to the cells through tiny tubes called capillaries (cap-ill-air-ies). Blood then returns to the heart through the veins (vayns) and the cycle begins again.read more >>