Britannica Educational Publishing 
Respiratory System [PDF ebook] 

So automatic and mechanical is breathing for most of us that we often fail to consider the complexities of respiration. Engaging the lungs, airways, and more, the intake of oxygen and release of carbon dioxide are only the most apparent aspects of a much longer routine. Although vulnerable to various infections and other disorders, the respiratory system by and large continues to function in order to sustain us. This book explores each element involved in this subconscious process and the factors that perpetuate human life.