Final answer:
The pressures inside the thoracic cavity change during breathing due to the contraction and relaxation of the diaphragm and intercostal muscles. During inhalation, the thoracic cavity expands and pressure drops, allowing air to flow in. During exhalation, the cavity's volume decreases and pressure increases, expelling air.
Step-by-step explanation:
Pressure changes within the thoracic cavity of a mammal are integral to the process of breathing and are largely governed by Boyle's law, which expresses an inverse relationship between pressure and volume.
During inhalation, the diaphragm contracts and flattens, while the intercostal muscles contract, leading to the expansion of the thoracic cavity. This expansion causes a decrease in pressure within the cavity, making it lower than the atmospheric pressure. As a result, air flows into the lungs, following the gradient from higher to lower pressure.
Conversely, expiration is typically a passive process where the diaphragm and intercostal muscles relax, leading to a decrease in thoracic volume and an increase in pressure, causing air to flow out of the lungs.
The concept of thoracic wall compliance also plays a role in the ease with which these pressure changes can occur. If the thoracic wall is not compliant, it becomes difficult to change the cavity's volume and thus alter the pressures necessary for breathing.
A disruption in this system, such as from a puncture wound to the thoracic cavity, can impede the generation of negative pressure necessary for inhalation. Similarly, increased airway resistance could affect intrapleural pressure, complicating the process of inhalation and requiring more effort to inspire air.