Oxygen enters the lungs via inspired air and diffuses across the alveoli membranes to enter the blood. At the same time, carbon dioxide leaves the blood by diffusion through the alveoli and is expired.
In the tissues, the opposite occurs—oxygen leaves the blood to oxygenate the tissue. Carbon dioxide, a waste product from tissue activity, leaves the tissue and enters the blood where it is carried to the lungs for expiration.
Several conditions are necessary for adequate tissue oxygenation:
- oxygen available in the atmosphere
- adequate ventilation
- exchange of gas between the lungs and arterial blood
- loading of oxygen onto hemoglobin
- sufficient amount of hemoglobin
- satisfactory blood flow to the tissues
- oxygen release to the tissues
If there are disruptions in any of these conditions, hypoxia can result.
