Explain the difference between anatomic and physiological dead space.

Within the conducting airways, no gas exchange in and out of the body occurs; this makes up the anatomic dead space volume of the lung. The section made up of the deeper airways of the lung continues to divide into smaller and smaller tubes. Because the conducting airways transfer the air only from the mouth to the respiratory zone, part of the tidal volume does not reach the gas exchange areas of the lung and, therefore, does not take part in gas exchange; it is identified as the anatomic dead space.

Some of the fresh air reaching the alveoli are not perfused, or are poorly perfused, by the blood carried in the lung's network of capillaries. These alveoli will not be able to exchange alveolar gas with the blood and are identified as additional dead space. The physiological dead space is the addition of dead space added to the anatomic dead space, and is therefore larger than the anatomic dead space.