What is the process of external respiration?

External respiration refers specifically to the exchange of gases between the lungs and the blood in the pulmonary capillaries. This process occurs when oxygen is taken in from the air in the lungs and diffuses into the bloodstream, while carbon dioxide, which is a waste product of metabolism in the body's cells, moves from the blood into the alveoli in the lungs to be exhaled. This critical exchange ensures that oxygen reaches the blood, which then transports it to the tissues, and that carbon dioxide is removed from the body.

Other options describe different aspects of respiratory physiology but do not accurately reflect the definition of external respiration. For example, the exchange of gases between blood and tissues pertains to internal respiration, which occurs at the cellular level. The transport of oxygen in the bloodstream is part of the circulatory process but does not involve the direct exchange mechanisms that characterize external respiration. Lastly, the inhalation and exhalation process primarily relates to the mechanics of breathing rather than the specific gas exchange taking place between the lungs and the blood.