11 Biology

Respiration in Human

MECHANISM OF BREATHING

Breathing involves two stages, viz. inspiration and expiration. The atmospheric air is drawn in during inspiration and the alveolar air is released out during expiration. The movement of air into and out of the lungs is facilitated by creating a pressure gradient between the lungs and the atmosphere. When the pressure within the lungs is less than the atmospheric pressure, inspiration takes place. When the intra-pulmonary pressure is higher than the atmospheric pressure, expiration takes place.

The pressure gradient is generated by the diaphragm and a specialized set of muscles. These special muscles are external and internal intercostals between the ribs.


Mechanism of Inspiration:

  • Inspiration is initiated by the contraction of diaphragm.
  • The contraction of diaphragm increases the volume of thoracic chamber in the antero-posterior axis.
  • The external inter-costal muscles contract to lift up the ribs and the sternum. This causes an increase in the volume of the thoracic chamber in the dorso-ventral axis.
  • The overall increase in the thoracic volume results in a similar increase in pulmonary volume.
  • The increase in pulmonary volume decreases the intra-pulmonary pressure to less than the atmospheric pressure.
  • This pressure gradient forces the air from outside to move into the lungs and inspiration takes place.

Mechanism of Expiration:

  • Diaphragm and inter-costal muscles relax which results in the diaphragm and the sternum returning to their normal positions.
  • This reduces the thoracic volume and thus the pulmonary volume.
  • The reduction in pulmonary volume results in an increase in intra-pulmonary pressure to slightly above the atmospheric pressure, which causes the expulsion of air from the lungs, and expiration takes place.




REGULATION OF RESPIRATION

The regulation of respiration is done by the neural system. The respiratory rhythm centre is present in the medulla and is mainly responsible for the regulation of respiration. Another region; called pneumotaxic centre is present in the pons. The pneumotaxic centre can moderate the functions of the respiratory rhythm centre.

A chemosensitive area is situated adjacent to the rhythm centre. This is highly sensitive to CO2 and hydrogen ions. Increase in these substances can activate this chemosensitive area. This; in turn; gives signal to the rhythm centre to make necessary adjustments in the respiratory process so that these substances can be eliminated.

Receptors associated with aortic arch and carotid artery can also recognize changes in CO2 and H+ concentration. These receptors send necessary signals to the rhythm centre for corrective actions.

It is important to remember that the role of oxygen in the regulation of respiratory rhythm is quite insignificant.



DISORDERS OF RESPIRATORY SYSTEM

Asthma: Asthma is a difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles. Constriction of bronchii leads to asthmatic attacks.

Emphysema: Emphysema is a chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased. Smoking is a major cause of emphysema.

Occupational Respiratory Disorders: In some industries, a huge amount of dust is involved. The dust particles often get inside the lungs of the workers because the body’s defence system is unable to cope with the huge amount of dust. Long term exposure can lead to severe lung damage. Workers usually wear masks to prevent the entry of dust particles inside their lungs.

DO YOU KNOW? Minute blisters formed inside lungs due to inhalation of silicon dust are symptoms of a disease called PNEUMATOULTRAMICROSCOPICSILICOVOLCANOSIS. In short, it is called pneumoconiosis.