What is the term for the thin lubricating fluid between pleural membranes?

• A. Blood
• B. Pleural fluid
• C. Lymph
• D. Synovial fluid

Answer: (B)

The term for the thin lubricating fluid between pleural membranes is pleural fluid. This serous fluid fills the pleural space between the visceral and parietal pleura, allowing them to slide smoothly past each other as the lungs expand and contract, which minimizes friction during breathing. It’s produced by the pleural membranes and surrounding capillaries and is normally present in small amounts, helping maintain a slight negative pressure that assists lung expansion. The other fluids listed relate to different parts of the body: blood is inside vessels, lymph circulates through the lymphatic system, and synovial fluid lubricates joints.