The Mechanism and Regulation of Breathing

The Mechanism and Regulation of Breathing

Breathing is an involuntary movement that is controlled by the

medulla, which is part of the hind brain. Air is sucked into the lungs

by an active process called inspiration. The external intercostals

muscle contract and the internal intercostals muscle relax this causes

the ribs to be drawn upwards and outwards. While this is happening the

diaphragm muscles contracts and pushes down towards the abdomen. The

lungs are made to expand because the pleural surfaces of the lungs are

attached to the pleural on the chest wall; this increases the volume

of the air spaces and drops the air pressure in the lungs so that air

rushes in.

Expiration is mainly an involuntary reaction to the external

intercostals and diaphragm muscles relaxing. The elastic fibres in the

stretched lung are recoiled which allows the ribs and diaphragm to

return to their original position. Air pressure in the lungs rise to

just above atmospheric pressure therefore the air is expelled.

Regulation of breathing is controlled by the respiratory centre in the

hind brain. The respiratory centre has three areas called the

medullary rhythmicity area, the apneustic area and the pneumotaxic

area. Basic rhythm of inspiration and expiration is controlled by the

medullary rhythmicity area. Nerve impulses from the apneustic area can

alter the depth of breathing and nerve impulses from the pneumotaxic

area can alter the breathing rate.

The respiratory centre is influenced by many sensory signals which

indicate what changes need to be done to the regulation of breathing.

One of the most important changes would be an alteration in the

concentration of hydrogen ions in the blood this could be caused by a

rise in blood carbon dioxide or an increase in tissue respiration in

the muscles during exercise. The respiratory centre is in its self

sensitive to raised hCo2 and responds by increasing the rate and depth

of breathing.

In the aortic arch and carotid bodies there are chemoreceptors these

sense changes to the blood oxygen tension but only respond to a large