What physiological change occurs during inhalation?

• A. The diaphragm contracts and moves upward
• B. The diaphragm contracts and moves downward
• C. The rib cage shrinks
• D. The lungs collapse

Answer: (B)

During inhalation, the diaphragm contracts and moves downward, leading to a decrease in pressure within the thoracic cavity. This pressure change allows air to flow into the lungs. When the diaphragm contracts, it increases the volume of the thoracic cavity, which, according to the principles of physics, results in a drop in internal pressure. This creates an area of lower pressure relative to the outside atmosphere, causing the air to rush into the lungs to equalize the pressure difference.

The downward movement of the diaphragm is critical as it expands the lungs further, allowing more air to fill them. This mechanism is essential for effective gas exchange, as it facilitates the intake of oxygen-rich air while preparing for the expulsion of carbon dioxide.