Which structure marks the boundary between the thoracic and abdominal cavities?

Which structure marks the boundary between the thoracic and abdominal cavities?

• A. Pleural cavity
• B. Pericardial sac
• C. Diaphragm
• D. Mediastinum

Answer: (C)

The boundary between the thoracic and abdominal cavities is the diaphragm. This muscular sheet forms the floor of the thoracic cavity and the roof of the abdominal cavity, effectively dividing the two spaces. It sits between the lungs/heart in the thorax and the digestive organs in the abdomen, and its downward movement during inhalation expands the thoracic cavity while reducing the abdominal space. The pleural cavities, pericardial sac, and mediastinum are all contained within the thoracic cavity, not at the boundary; the diaphragm is the physical partition that separates the two cavities.

The boundary between the thoracic and abdominal cavities is the diaphragm. This muscular sheet forms the floor of the thoracic cavity and the roof of the abdominal cavity, effectively dividing the two spaces. It sits between the lungs/heart in the thorax and the digestive organs in the abdomen, and its downward movement during inhalation expands the thoracic cavity while reducing the abdominal space. The pleural cavities, pericardial sac, and mediastinum are all contained within the thoracic cavity, not at the boundary; the diaphragm is the physical partition that separates the two cavities.