Zoology - Breathing and Exchange of Gases Question with Solution | TestHub

Inspiration can occur if the intra-pulmonary pressure is less than the atmospheric pressure, i.e., there is a positive pressure in the lungs with respect to atmospheric pressure.

Expiration can occur if the intra-pulmonary pressure is more than the atmospheric pressure, i.e., there is a negative pressure in the lungs with respect to atmospheric pressure.

Inspiration is initiated by the contraction of diaphragm which increases the volume of thoracic chamber in the antero-posterior axis.

The contraction of external intercostal muscles lifts up the ribs and the sternum causing an increase in the volume of the thoracic chamber in the antero-posterior axis.