Question
Explain the process of inspiration and expiration under normal conditions.
✓
Answer
Inspiration:
- Inspiration is initiated by the contraction of diaphragm, which increases the volume of the thoracic chamber along the antero-posterior axis.
- The contraction of external inter-costal muscles lifts up the ribs and the sternum; this causes an increase in the volume of the thoracic chamber along the dorso-ventral axis.
- The increase in the pulmonary volume causes a decrease in the intra-pulmonary pressure which becomes less than the atmospheric pressure.
- Hence, air rushes from outside into the lungs, i.e. inspiration.
- The relaxation of the diaphragm and the intercostal muscles returns the diaphragm and the ribs and sternum to their original position.
- This causes a decrease in the volume of the thoracic chamber and thereby the pulmonary volume.
- This leads to an increase in the intra-pulmonary pressure a little higher than atmospheric pressure and hence, the air rushes out of the lungs to the atmosphere, i.e. expiration.
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