Answer:
The correct answer to the question: During inhalation, which changes first in the thoracic cavity, the pressure or the volume, is, the volume.
Explanation:
The process of breathing, that is the cylces of inhalation and inspiration, are completely dependent on pressure gradients both on the atmosphere and inside the body, specifically the lungs and thoracic cavity. Before the breathing is initiated, both the atmospheric and alveolar pressures (alveoli are where the exchange of oxygen and carbon dioxide will take place), is equal. However, during the initiation of inspiration, the costal muscles and the diaphragm descend and open up the chest cavity, pulling with them the lungs. This causes an increase in volume capacity and a decrease of pressure within the alveoli. Since gases like oxygen tend to move from higher to lower pressure gradients, as the volume of the lungs increases, and pressure decreases, oxygen will flow from the atmosphere into the lungs. During expiration, as the lungs return to their normal state, volume diminishes, pressure increase, and the gases are thus expelled to normalize pressures again.
