Final answer:
When the pleural cavity is entered, such as by a bullet penetrating a lung, the visceral pleura is the first serous membrane layer encountered. This can result in pneumothorax, affecting the negative intrapleural pressure necessary for lung expansion and potentially impacting other cavities like the superior mediastinum and pericardial cavity.
Step-by-step explanation:
Understanding Entry to the Pleural Cavity
If a bullet were to penetrate a lung, the pleural cavity would be entered, potentially causing a pneumothorax, or collapsed lung. This injury can compromise breathing by interrupting the negative intrapleural pressure that is vital for lung expansion. The visceral pleura, which is the layer of the serous membrane directly covering the lungs, would be the first to be encountered by an object penetrating the thoracic cavity. Additionally, such a trauma might also affect the superior mediastinum and the pericardial cavity if the trajectory of the bullet is such that these cavities are in its path.
Increased airway resistance could lead to a rise in intrapleural pressure during inhalation, as it would make it more difficult to expand the lungs against the resistance. A puncture to the thoracic cavity, such as from a knife wound, would also disrupt the finely balanced forces that allow for normal inhalation. These forces create the negative intrapleural pressure necessary for lung expansion. If disrupted by a puncture, the lung may collapse due to the loss of negative pressure, resulting in a spontaneous pneumothorax and impaired ability to inhale.