Lungs do not collapse between breaths and some air always remains in the lungs which can never be expelled because

Options

A. there is a negative pressure in the lungs
B. there is a negative intrapleurai pressure pulling at the lungs walls
C. there is a positive intrapleural pressure
D. pressure in the lungs is higher than the atmospheric pressure

Answer

B

Explanation

Lungs do not collapse between breaths and some air always remain in the lungs, which can be never expelled, because there is a negative inrapleural pressure pulling the lung walls. Alveoli are basic funcational unit of lungs. The outer alveolar wall surface have cells, which secrets DPPC also called as lipid surfactant. The surfactant expands the alveoli. Due to which the negative pressure inside the alveoli increase. this prevents the alveoli from collapsing .