PATHOLOGY

Detailed explanation-1: -Inspiration can occur if the pressure within the lungs (intrapulmonary pressure ) is less than the atmospheric pressure, i.e., there is a negative pressure in the lungs with respect to atmospheric pressure. Similarly, expiration takes place when the intrapulmonary pressure is higher than the atmospheric pressure.

Detailed explanation-2: -Alveolar pressure is given with respect to atmospheric pressure, which is always set tozero. Thus, when alveolar pressure exceeds atmospheric pressure, it is positive; when alveolarpressure is below atmospheric pressure it is negative. Alveolar pressure determines whether air will flow into or out of the lungs.

Detailed explanation-3: -When the air pressure within the alveolar spaces falls below atmospheric pressure, air enters the lungs (inspiration), provided the larynx is open; when the air pressure within the alveoli exceeds atmospheric pressure, air is blown from the lungs (expiration).