Ventilation activity

In inspiration the diaphragm and external intercostal muscles contract. This causes the diaphragm to flatten and the thoracic cage to move upward and outward. This increases the volume of the thorax and creates a negative pressure. Air rushes in to equilibrate the pressure in the thorax with the atmospheric pressure outside. Inspiration is an active process since it involves muscle contraction.

Expiration is a passive process in which the diaphragm relaxes and resumes its dome shape and the external intercostal muscles relax enabling the thoracic cage to move downwards and inwards. The thoracic volume reduces and air is forced out of the lungs due to the elastic recoil of lung tissues and from surface tension within the alveoli.

See how much you've learnt about ventilation with the interactive activity below.

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