Pleural pressure at the end of inspiration is -

Ans. is 'b' i.e.. More negative o During quiet breathing, the intrapleural pressure fluctuates between -3 and -6 mm Hg, depending upon the phase of respiration, more negative at the end of inspiration and less negative during expiration.Intrapleural pressure (Pleural pressure)o It is the pressure between two pleural surfaces. The lung is covered with visceral pleura and the thoracic cage is lined on inside with parietal pleura. Between the two layers of pleura is a very narrow space, called the pleural cavity. Intrapleural pressure is always negative and during quiet breathing the Intrapleural pressure fluctuates between -3.8 mm Hg (- 5.0 cm water)1 to -6.0 mm Hg (-8.0 cm water).o Now let us examine why the pleural pressure is negative; more negative during inspiration, less negative during expiraion, but always negative during quiet breathing. The key to the answer is the fact that both the thoracic cage and lungs are elastic structures. Being elastic structure they both tend to recoil, but in opposite direction. The lungs have a tendency to collapse and thoracic cage has a tendency to expand. However, because of the anatomical relationships in the body, these tendencies do not normally materialize. But the tendencies do create an inward pull on the visceral pleura (by lung) and an outward pull on parietal pleura (by thoracic cage). The results of these pulls is a negative pressure in the space between the pleural surfaces, i.e., in the pleural cavity.