Final answer:
Gas exchange occurs in three phases: 1) Breathing, moving air in and out of the lungs; 2) Diffusion of gases across respiratory surfaces in the alveoli due to concentration gradients; and 3) Transport of gases in the blood between the lungs and tissues.
Step-by-step explanation:
Gas exchange takes place in three phases: ventilation (breathing), diffusion across respiratory surfaces, and transport of gases within the body. During ventilation, air is moved into and out of the lungs, primarily in the alveoli, which is where the gas exchange with blood occurs. Diffusion is driven by concentration gradients, where oxygen moves from areas of high concentration in the lungs to low concentration in the blood, and carbon dioxide moves in the opposite direction. Finally, the transport of gases involves carrying oxygen and carbon dioxide to and from the tissues and lungs via the bloodstream.
In the alveoli, the intra-alveolar pressure promotes the movement of air in and out with each breath, facilitating the diffusion of gases. The extensive network of alveoli provides a large surface area for gas exchange, maximizing efficiency. This process is supported by the circulatory system, which moves oxygen-depleted blood to the lungs and oxygen-rich blood to the rest of the body.