What is the purpose of the pleural fluid that surrounds the lungs? To protect against friction during breathing. To exchange oxygen for carbon dioxide. To create negative pressure in the thoracic cavity. To maintain the temperature within the lungs.

The purpose of the pleural fluid that surrounds the lungs is to protect against friction during breathing. The pleural fluid is a thin layer of fluid that surrounds the lungs and lines the inside of the chest cavity. This fluid acts as a lubricant, allowing the lungs to move smoothly against the chest wall during breathing. It helps to reduce friction and prevent damage to the lung tissue and the chest wall. The other options provided are not the primary functions of the pleural fluid. Oxygen and carbon dioxide exchange occurs in the alveoli of the lungs, not the pleural fluid. The negative pressure in the thoracic cavity is created by the diaphragm and intercostal muscles, not the pleural fluid. The temperature within the lungs is regulated by the body's thermoregulatory mechanisms, not the pleural fluid.