The Mechanism and Regulation of Breathing.

Angela Carpenter

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 ...

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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 drop in oxygen. Baroreceptors are also found in the aortic arch and carotid bodies and these are sensitive to a change in blood pressure. The ph of the blood is monitored by the peripheral chemoreceptors. In the walls of the bronchi and bronchioles there and stretch receptors which are simulated by overstretching during excessive inspiration.

The control of breathing is a complex interaction and can be influenced by many other factors e.g. raised body temperature, pain and emotion. There is also an ability to control and alter our breathing voluntary for various reasons such as speaking, yawning or coughing.

Reference: Advanced human biology. J Simpkins. J I Williams.