What is the process of pulmonary ventilation?

The process of pulmonary ventilation specifically refers to the mechanical movement of air into and out of the lungs, which is critical for respiration. This involves two main phases: inhalation (or inspiration) and exhalation (or expiration). During inhalation, air is drawn into the lungs as the diaphragm contracts and the thoracic cavity expands, creating a negative pressure that allows for the intake of atmospheric air. Conversely, during exhalation, the diaphragm relaxes, and the elastic recoil of lung tissues helps to push air out of the lungs.

The other options describe important physiological processes related to respiration but do not accurately define pulmonary ventilation. For example, the absorption of gases by alveoli pertains to the process of gas exchange rather than the physical movement of air. The exchange of gases in the bloodstream refers to the transfer of oxygen and carbon dioxide between the alveoli and the blood, a secondary process following ventilation. Lastly, the control of gas levels in tissues involves various metabolic processes and the regulation of breathing but does not encompass the act of moving air in and out of the lungs.

Thus, the flow of air into and out of the lungs is the defining characteristic of pulmonary ventilation, confirming why this choice is the correct answer.