During inspiration, which of the following occurs?

• A. Diaphragm descends
• B. Diaphragm ascends
• C. Intra-abdominal pressure decreases
• D. Intra-thoracic pressure increases

Answer: (A)

During inspiration the diaphragm contracts and moves downward, enlarging the thoracic cavity. This downward movement increases thoracic volume and lowers intrathoracic pressure below atmospheric level, creating a negative pressure gradient that pulls air into the lungs. The diaphragm does not ascend during inspiration; and intrathoracic pressure does not rise—inspiration actually lowers it. While the abdominal contents are pushed downward, causing a slight rise in intra-abdominal pressure, the key observable effect related to air flow is the diaphragmatic descent and the resulting drop in intrathoracic pressure.