When the diaphragm and intercostal muscles relax, which one of the following occurs?

When the diaphragm and intercostal muscles relax, exhalation occurs. This process is a key component of the respiratory cycle. During inhalation, these muscles contract, causing the thoracic cavity to expand and air to flow into the lungs. However, once the diaphragm and intercostal muscles relax, the volume of the thoracic cavity decreases, which increases the pressure in the lungs relative to the outside atmosphere. This pressure change facilitates the movement of air out of the lungs and into the environment, leading to exhalation.

Understanding this mechanism is essential in emergency care situations, as recognizing normal versus abnormal breathing patterns can provide crucial information about a patient's respiratory status. While oxygenation refers to the process of delivering oxygen to cells and ventilation pertains to the movement of air in and out of the lungs, the immediate outcome of muscle relaxation is the act of exhalation itself.