Mechanism of Breathing: Introduction to Breathing, What is Breathing (For CBSE, ICSE, IAS, NET, NRA 2022)

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Introduction to Breathing

  • Breathing can be defined as the process in which air moves in and out of the lungs.
  • This is carried out through various respiratory organs.
  • In simple words one can define breathing as the simple give and take process.
  • Breathing is a continuous process and goes on throughout the life of an organism.
  • Inhalation is the process of taking in oxygen-rich air and exhalation is the process of giving out air that is rich in carbon dioxide.
  • The breathing is of an adult is 15 - 18 times per minute.
  • Breathing rate exceeds 25 times per minute during a heavy exercise.
Quiet Breathing
Forceful Breathing

Breathing Mechanism

Inspiration Expiration


  • It involves contraction of muscles attached to the ribs along the outer side.
  • There is an expansion in the chest cavity.
  • The diaphragm, contracts, moves downwards, and expands the chest cavity.
    • Results in the contraction of the abdominal muscles.
  • A partial vacuum is produced by the expansion the chest cavity which sucks air into the lungs and fills the expanded alveoli.

Mechanism of Inspiration

  • The process of intake of atmospheric air is called inspiration.
  • Inspiration occurs when the volume the muscles of the diaphragm and the abdomen relax.
  • The air pressure inside the lungs decreases.


  • This occurs after the gaseous exchange in the lungs and the air is expelled out.
  • Expiration is the expulsion of air.
  • The muscles attached to the ribs contract.
  • The muscles of the diaphragm and the abdomen relax.
  • The air in the lungs is pushed out through the nose.

Mechanism of Expiration

  • Expiration is the process of exhaling carbon dioxide.
  • The size of thoracic cavity decreases and there is an increase in the air pressure outside.
  • Here the diaphragm relaxes, and the lungs get compressed.
  • The pressure increases and the air is forced outside.

Internal Respiration

  • The exchange of gases in the tissue is called internal respiration.
  • The oxygen is carried in the form of Oxyhaemoglobin gets dissociated to release oxygen.
  • The glucose is broken down by the oxygen to release carbon dioxide, water, and energy.
  • The carbon dioxide is diffused from the tissues while the energy is utilized by the body.

Intrapleural Breathing

  • It refers to the pressure that is present in the space between the pleura and the lungs.
  • The space is called pleural cavity.
  • Pleural pressure is termed as negative pressure.
    • The pressure in this region is normally less than the atmospheric pressure.
The Pleural Cavity

Difference between Breathing and Respiration

Difference between Breathing and Respiration
It involves the process of inhalation and exhalation.It takes place in cells.
It is a voluntary physical process.It is the process of breaking down of glucose to produce energy.
It takes place in the lungs.It is an involuntary chemical process.
No energy is produced in the process.Energy is released in the form of ATP.
There is no use of enzymes.A large no. of enzymes is used during the process.

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