Explain the mechanism of breathing ( class 11 )

1.	Explain the mechanism of breathing ( class 11 )
Answer» MECHANISM OF BREATHING\tBreathing involves two stages :\tInspiration- during which atmospheric air is drawn in.\tExpiration- during which the alveolar air is released out.\tInspiration can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure.\tExpiration takes place when the intra-pulmonary pressure is higher than the atmospheric pressure.\tThe diaphragm and a specialised set of muscles – external and internal intercostals between the ribs.\tThe contraction of external inter-costal muscles lifts up the ribs and the sternum causes an increase in the volume of the thoracic chamber in the dorso-ventral axis.\tAn increase in pulmonary volume decreases the intra-pulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into the lungs.\tRelaxation of the diaphragm and the inter-costal muscles returns the diaphragm and sternum to their normal positions and reduce the thoracic volume and thereby the pulmonary volume, which leads to an increase in intra-pulmonary pressure to slightly above the atmospheric pressure causing the expulsion of air from the lungs.\tA healthy human breathes 12-16 times/minute.\tThe volume of air involved in breathing movements can be estimated by using a\xa0spirometer.

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