Pleura is defined as what?

• A. Layer of muscle between the ribs
• B. Membrane that surrounds the lungs and lines the thoracic cavity
• C. Gas in the pleural cavity
• D. Air sacs inside lungs

Answer: (B)

Pleura is a serous membrane that surrounds the lungs and lines the inside of the chest wall. It has two layers: the visceral pleura adheres to the surface of the lungs, and the parietal pleura lines the thoracic cavity, including the diaphragm and mediastinum. Between these layers is the pleural space, which contains a small amount of lubricating fluid that allows the lungs to move smoothly during breathing and helps create a slight negative pressure to keep the lungs inflated. This definition fits because pleura is specifically a membrane, not a muscle, gas, or the air sacs inside the lungs.