Introduction

Every breath we take answers a question most of us never stop to ask: why is breathing necessary at all? The answer lies in how the body gets its energy. Cells break down glucose and other biomolecules to release the energy needed for every life process, and this breakdown depends on a continuous supply of oxygen. The same reaction also produces carbon dioxide as a by-product, which is harmful if allowed to accumulate. So a living body must constantly bring oxygen in and push carbon dioxide out - and the respiratory system exists to make that exchange possible.

Building on the earlier discussion of how food supplies energy for growth and tissue repair, this chapter turns to how that oxygen actually reaches the body's cells. It looks at the respiratory organs of the human body, how breathing mechanically happens, how gases are exchanged and transported in the blood, and some common disorders of the respiratory system. Respiration itself can be defined as the exchange of oxygen and carbon dioxide between the environment and the body's cells, coupled with the enzymatic breakdown of nutrients inside those cells to release usable energy.