Mechanism of Breathing - Process
Description:
Inspiration
Occurs when the pressure within the lungs is less than the atmospheric pressure i.e. negative pressure in lungs with respect to atmospheric pressure.
Involves the intake of fresh air in the alveoli of the lungs.
It involves muscle contraction hence it is an active process.
Changes occurring during inspiration
Contraction of external inter-costal muscles: Lifts up the ribs and the sternum causing an increase in the volume of the thoracic chamber.
Contraction of diaphragm: Increases the volume of thoracic chamber.
The overall change in the volume of the thoracic chamber increase the pulmonary volume.
Increase in the pulmonary volume decreases the intra pulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into the lungs.
Expiration
- Takes place when the intra-pulmonary pressure is higher than the atmospheric pressure.
- Involves the expelling of foul air out of the body.
- It is a passive process and involves the relaxation of inspiratory muscles.
Changes occurring during expiration
Relaxation of the diaphragm.
Relaxation of the inter-costal muscles.
Relaxation of diaphragm, intercostal muscles and sternum causes the decrease in the thoracic volume and hence decrease in the pulmonary volume.
Increase in the pulmonary pressure more than the atmospheric pressure causing the expulsion of air out of the lungs.
The strength of inspiration and expiration can be further increased with the help of additional muscles in the abdomen.
A healthy human breathes 12-16 times/minute.
Volume of air in breathing movement is estimated by using an instrument called spirometer.