. Explain mechanism of Breathing

Best Answer

(a) Inspiration
1. It is an active process which involves contraction of diaphragm (Phrenic muscle) and External Inter Costal Muscles (EICM). 
2. Diaphragm is responsible for 80% of breathing volume during quiet normal breathing and EICM are responsible for (20-25%).
3. The diaphragm-muscles contract and the dome shape of diaphragm changes to flat. With the contraction, the lower surface of the lungs is also pulled downward. 
4. The external inter-costal muscles contract and the ribs move outward upward and formation to increase the volume of thoracic cavity.
5. Lungs expand and air is drawn into the lungs. The lungs in human, like other mammals, are negative (-ve) pressure type. Inspiration can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure
(b) Expiration
1. Quiet expiration is a passive process or elastic recoil process, which occurs due to relaxation of diaphragm and EICM.
2. The diaphragm becomes dome shaped again.
3. In forced expiration, the internal inter-costal muscles and abdominal muscles contract. This is an active process.
Respiratory volumes and capacities
The volume of air involved in breathing movements can be estimated by using a spirometer which helps in clinical assessment of pulmonary functions.


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