Which structure separates the thoracic cavity from the abdominal cavity?

Which structure separates the thoracic cavity from the abdominal cavity?

• A. The sternum
• B. The mediastinum
• C. The diaphragm
• D. The rib cage

Answer: (C)

The diaphragm serves as the primary physical boundary between the thoracic and abdominal cavities. It is a dome-shaped muscle that forms the floor of the chest and the roof of the abdomen. When it contracts, it flattens and moves downward, enlarging the thoracic cavity to draw in air; when relaxed, it moves upward toward the chest. This movement creates a clear separation between the organs of the chest and those in the abdomen. The sternum and rib cage shape the chest wall but do not act as the dividing boundary, and the mediastinum is a central chest space inside the thoracic cavity, not the separating barrier itself.

The diaphragm serves as the primary physical boundary between the thoracic and abdominal cavities. It is a dome-shaped muscle that forms the floor of the chest and the roof of the abdomen. When it contracts, it flattens and moves downward, enlarging the thoracic cavity to draw in air; when relaxed, it moves upward toward the chest. This movement creates a clear separation between the organs of the chest and those in the abdomen. The sternum and rib cage shape the chest wall but do not act as the dividing boundary, and the mediastinum is a central chest space inside the thoracic cavity, not the separating barrier itself.