1. Ventilation: This is the process of moving air in and out of the lungs. It involves the physical act of breathing, where air is inhaled into the lungs and exhaled out of the lungs. This is facilitated by the expansion and contraction of the chest cavity.
2. Diffusion: This is the movement of gases from an area of high concentration to an area of low concentration. In the lungs, oxygen from the inhaled air diffuses across the thin walls of the alveoli (tiny air sacs) into the blood. At the same time, carbon dioxide diffuses from the blood into the alveoli to be exhaled.
3. Perfusion: This refers to the blood flow through the capillaries surrounding the alveoli. This allows the blood to carry the oxygen picked up from the alveoli to the rest of the body and carry the carbon dioxide from the body back to the lungs to be exhaled.
These three phases work together to ensure the continuous exchange of gases between the environment and the cells of the body.
