ABSTRACT
Studying physiology and pathology necessitates reductionism, but body systems function as parts of the whole body, not in isolation. Cardiovascular and respiratory functions are particularly closely interdependent: delivering oxygen and nutrients to tissues, while removing carbon dioxide and other waste. Respiration should achieve adequate tissue oxygenation, so gas movement across lung membranes forms external respiration, gas movement between tissue cells and capillaries forms internal respiration.
