Inspiration and Expiration

Inspiration and Expiration

The Process of Inspiration (Inhalation)

  • Inspiration is an active process primarily involving the diaphragm and the intercostal muscles in your chest.

  • When you inhale, the diaphragm contracts and moves downwards, increasing the space in your chest cavity.

  • The external intercostal muscles also contract, causing the rib cage to expand outwards and upwards, further increasing the chest cavity’s volume.

  • The increase in volume leads to a drop in pressure inside the chest cavity (it becomes less than the atmospheric pressure outside the body).

  • The pressure difference then causes air to be drawn into the lungs.

The Composition of Inhaled Air

  • The air we inhale primarily consists of 78% nitrogen, 21% oxygen, and small amounts of other gases like carbon dioxide and argon.

  • While air also contains 0.04% carbon dioxide, as we will see, the role of carbon dioxide in the body is integral to the process of respiration.

The Process of Expiration (Exhalation)

  • Expiration, unlike inspiration, can be either passive or active.

  • Passive expiration is the most common and occurs when the diaphragm and intercostal muscles relax.

  • The relaxation reduces the size of the chest cavity, increasing the pressure inside (it becomes greater than the atmospheric pressure).

  • This differential pressure forces air out of the lungs.

  • Active expiration, which happens during vigorous exercise or in conditions like chronic obstructive pulmonary disease (COPD), additionally involves contraction of the muscles in the abdomen, forcing more air out and increasing respiratory rate.

The Composition of Exhaled Air

  • The air exhaled is distinctly different from the inhaled air, primarily consisting of 78% nitrogen, 16% oxygen, and 4% carbon dioxide.

  • Other gases are present in similar or slightly increased amounts. Most importantly, relative concentration of carbon dioxide is significantly higher due to it being a by-product of cellular respiration.

Understanding the functioning of the respiratory system and the processes of inspiration and expiration are fundamental to studying health and social care as these processes maintain the oxygen-carbon dioxide balance in our bodies, crucial for maintaining life and normal cell function.