Question

Pressure gradient between the lungs and atmosphere is generated by a- diaphragm, b- external intercostal muscles, c- internal intercostal muscles, d- ribs

Answer 1

Pressure gradient due to contraction of diaphragm and external intercostal muscles

The contraction of diaphragm and external intercostal muscles causes the thoracic volume to increase which in turn raises the pulmonary volume. Increase in the pulmonary volume decreases the intra-pulmonary pressure to less than the atmospheric pressure.

Hence air enters the lungs because of the pressure gradient created.

Pressure gradient due to relaxation of diaphragm and external intercostal muscles

The relaxation of diaphragm and external intercostal muscles causes the thoracic volume to decrease which in turn decreases the pulmonary volume. Decrease in the pulmonary volume Increases the intra-pulmonary pressure to more than the atmospheric pressure.

Hence air exits the lungs because of the pressure gradient created.

Contraction of internal intercostal muscles

The contraction of internal intercostal muscles decreases the diameter of the thoracic cavity along the antero-posterior axis, hence the Intra-pulmonary pressure increases than the atmospheric pressure. This leads to exhalation of air.