Loading : MECHANISMS OF RESPIRATION DURING QUIET AND FORCEFUL BREATHING  

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MECHANICS OF RESPIRATION
DURING 
QUIET AND FORCEFUL BREATHING
QUIET INSPIRATION:

The suprapleural membrane is fixed and cannot be raised or lowered. Conversely, the diaphragm is highly mobile and is in fact the primary muscle of respiration. When it contracts, the domes become flattened and when it relaxes they bulge again. In this way, the contraction of diaphragm increases the vertical diameter of the thoracic cavity.
VERTICAL DIAMETER:
Anteroposterior diameter
It is the diameter that can be drawn between the sternum and the verterbral column. In normal stature, the ribs slope downward and if they can be raised upward, like the handle of a bucket, the anteroposterior diameter can increase with sternum being thrust forward. This is done by fixing the first rib by the scaleni muscles of the neck and then contracting the intercostals muscles. Thus, all the ribs are drawn together and the sternum is thrust forward, which increases the anteroposterior diameter of the thoracic cavity
Transverse diameter:
It is the diameter between right and left sides of the rib cage. The joints with the vertebral column are moveable, which allow rotation about a transverse axis. . When the first rib is fixed and the intercostals muscles contract, the ribs rise upward and thus the transverse diameter is increased.

QUIET EXPIRATION;

It is brought about by elastic recoil of the lungs
Relaxation of intercostal muscles and diaphragm and increased tone in muscles of abdominal wall, which force the relaxing diaphragm upwards.
Forced Inspiration:
In deep forced inspiration, maximum increase in the capacity of thoracic cavity occurs. In this process, every muscle that can raise the rib is brought into action.

Lung changes during inspiration:
The root of the lung descends because it gets filled with air
Bifurcation of the trachea descends by about 2 vertebrae
To assist the pulmonary circulation, the alveolar capillaries dilate.
With expansion of the lungs, the elastic and connective tissue in the bronchial walls is stretched.
Forced expiration:

It is an active process brought about by forced contraction of muscles of anterior abdominal wall, which are assisted by other muscles. The quadratus lumborum muscle contracts and pulls the twelfth rib downwards. Now if some of the intercostals muscles contract, they will pull the ribs together towards the 12th rib and the volume of thoracic cavity will decrease. 
Lung changes on expiration:
Lung changes on expiration:


During expiration, the roots of lungs ascend.
The bronchi shorten and contract. 
The elastic tissue of the lungs recoil and they become reduced in size. 
The diaphragm moves upward costodiphragmatic recess deepens. 
The lower margins of the lungs, which rest on the diaphragm, rise (along the diaphragm) to a higher level.
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