Question

One of the following statements about pleural fluid and the pleural cavity is INCORRECT. Which one?

Pleural fluid is produced by the lung alveoli.

Pleural fluid is normally present in the pleural cavity.

The intrapleural pressure is always less than the intrapulmonary pressure.

The parietal pleura covers the superior part of the diaphragm.

Answer 1

Pleural fluid is produced by the lung alveoli.

Pleural fluid is a serous, thin, transparent fluid that is produced by the serous memebrane and most of it is produced by the parietal ciruculation (by the inercostal artries). The fluid is present in the pleural space (space between parietal and visceral pleura)  around the lungs when its rate of production exceeds the rate of reabsorption. Statement 3 is also correct as the intrapleural pressure is always Less than intrapulmonary pressure and atmospheric pressure. The parietal pleura is the outer membrane that covers the upper surface of the diaphragm.