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Respiratory Dead Space
Within the respiratory system there is physiological dead space where a portion of
the air inhaled does not participate in the exchange of oxygen and carbon dioxide.
This portion of the air, roughly a third of each breath, is “wasted”. Why is it wasted?
Some of the wasted air remains in the conducting airways or pathway leading to
the lung (anatomical dead space) and includes air within the mouth, trachea and
bronchioles. The rest of the air reaches the alveoli but may be poorly perfused
within the alveoli due to reduced blood flow to the alveolar capillaries or to lung
disease. This is known as alveolar dead space. The alveolar dead space combined
with the anatomical dead space adds up to the total physiological dead air space of
the respiratory system.
Think of this dead space like breathing through a tube. With every breath you
exhale, a certain portion of the air you inhale with next breath will be a mix of both
new fresh air coming in combined with some of the air you have just expelled what
is still trapped in the tube. Due to this mixing of air, air used inside our alveoli for
gas exchange contains less oxygen and more carbon dioxide than atmospheric air.
We will learn more about this as we study partial pressure later in this module.
What are the benefits of having respiratory dead space?
As a portion of the air sits
in this dead space it helps to accomplish the following: warming the air to body
temperature so hemoglobin will more readily bind to the oxygen in the air:
retaining carbon dioxide at a level higher than the atmospheric levels so that this
carbon dioxide may be used for maintaining the bicarbonate buffering system, and
giving the body time to humidify and clean the air by trapping matter in the mucous
lining before the air is used for gas exchange.