respiration

Respiration is the body's whole oxygen-delivery and carbon-dioxide-removal operation. Think of it as a supply line that runs from the air around you all the way to each cell, dropping off oxygen and carrying away the waste gas that cells produce while they burn fuel.

Doctors usually split respiration into stages. Ventilation moves air in and out of the lungs. External respiration is the exchange of gases between alveolar air and the blood. The blood then transports oxygen to the tissues and carbon dioxide back to the lungs. Internal respiration is the exchange of those gases between blood and the cells themselves.

There is also a cell-biology meaning of the word — cellular respiration, the chemistry inside mitochondria that uses oxygen to release energy. In everyday medical use, though, respiration usually refers to the breathing-and-gas-transport process as a whole, and that is the sense pulmonology is built around.