Question

How do we breathe?

Answer 1

Part 1: Breathing
Breathing is the physical process of exchange of gases with the atmosphere. It is completed in two phases:

• Inspiration: Uptake of oxygen rich atmospheric air into the lungs
• Expiration: Removal of carbon dioxide rich air outside into the atmosphere

Part 2: Inspiration
There is an increase in the volume of the thoracic chamber in the antero-posterior axis (due to contraction of the diaphragm) and in the dorso-ventral axis (due to contraction of external intercostal muscles). This leads to an increase in pulmonary volume. This increase in the volume decreases the intrapulmonary pressure to a value less than the atmospheric pressure. Creation of this pressure gradient forces the air from outside to move into the lungs.

Part 3: Expiration
There is a reduction in the volume of the chest cavity due to relaxation of the diaphragm and intercostal muscles. This increases the intrapulmonary pressure to a value more than the atmospheric pressure. Creation of this pressure gradient, in the reverse direction, forces the air to move out into the atmosphere.