1. Pulmonary gas exchange: This occurs in the lungs. Oxygen from the inhaled air diffuses from the alveoli (tiny air sacs in the lungs) into the bloodstream, specifically into the capillaries surrounding the alveoli.

2. Oxygen transport by the circulatory system: Once oxygen enters the bloodstream, it binds to hemoglobin, a protein within red blood cells. Hemoglobin transports oxygen throughout the body by binding to it in the arteries and releasing it in the capillaries.

3. Systemic gas exchange: In the systemic capillaries, oxygen diffuses out of the bloodstream and into the surrounding tissues. Oxygen moves from areas of higher concentration (the capillaries) to areas of lower concentration (the tissues) to meet the metabolic demands of the cells.