Final answer:
Nitrogen is the substance found in the highest concentration in the alveoli, followed by oxygen, water vapor, and carbon dioxide. The respiratory system regulates gas exchange based on the partial pressures and solubility of these gases.
Step-by-step explanation:
The substance found in the highest concentration in the alveoli is nitrogen. The composition of air in the alveoli is different from atmospheric air due to the processes of gas exchange. In the alveoli, the gases are present in the following relative concentrations: nitrogen > oxygen > water vapor > carbon dioxide, based on the information provided in Table 22.3. The primary goal of the respiratory system is the exchange of gases where oxygen is taken into the body and carbon dioxide is expelled.
Oxygen diffuses into the blood within the alveolar capillaries due to the pressure gradient while carbon dioxide diffuses from the blood into the alveoli, to be exhaled out of the body. This gas exchange is regulated by Dalton's law and Henry's law, which take into account the partial pressures of gases and their solubility in liquids, respectively.
The process of humidification increases the amount of water vapor in the alveolar air compared to atmospheric air. However, despite this increase, nitrogen remains the gas with the highest concentration in the alveoli.
Therefore answer is A. Oxygen.