Final answer:
The mechanism of action for changing gas tensions in the alveoli involves muscle movement and the role of surfactant in reducing alveolar surface tension, allowing efficient exchange of oxygen and carbon dioxide during breathing.
Step-by-step explanation:
The mechanism of action that decreases CO2 tension in the alveoli and increases O2 tension involves several physiological processes. When we inhale, the muscles in the diaphragm and rib cage contract, increasing the lung volume which leads to decreased pressure within the lungs. This allows air to flow in, bringing O2 into the alveoli. A substance known as surfactant, composed of lipoproteins, reduces the surface tension in the alveoli, preventing their collapse and aiding in the correct distribution of air among all alveoli, which is crucial for efficient gas exchange.
During exhalation, the diaphragm and intercostal muscles relax, intrapleural pressure returns to its resting state, and the elastic recoil of the lungs helps to expel air. Surfactant plays a further role by minimizing surface tension, which assists in keeping the alveoli open.
With each breath, the concentration of CO2 in the alveoli decreases and O2 increases, facilitating the dissociation of CO2 from hemoglobin and its diffusion into the alveoli to be exhaled. Meanwhile, O2 can bind to hemoglobin for transport to the tissues. This process also involve a reduction in H+ ions, helping to maintain blood pH within its normal range.