MCAT Biological and Biochemical Foundations Practice Exam 2026 – Complete Prep Guide

During inspiration, the process of breathing in air involves several physiological changes in the respiratory system that facilitate the entry of air into the lungs. One of the primary events is the elevation of the rib cage due to the contraction of the intercostal muscles. This elevation creates additional space within the thoracic cavity, leading to a reduction in pleural pressure. As the pressure inside the pleural cavity decreases, a pressure gradient is established, allowing air to flow into the lungs.

Furthermore, the contraction of the diaphragm, which is a dome-shaped muscle at the bottom of the thoracic cavity, also plays a crucial role in expanding the lungs. When the diaphragm contracts, it moves downward, further increasing the volume of the thoracic cavity. This combined action of the diaphragm and the rib cage elevating creates a larger volume in the thoracic cavity, facilitating the influx of air into the lungs.

While other options may include relevant physiological changes, they either do not encompass the essential aspects of the inspiration process or focus on elements not primarily associated with this phase of breathing. Thus, the elevation of the rib cage and the consequent reduction in pleural pressure are key components of inspiration that accurately reflect the underlying mechanics of how air enters the lungs.