What describes anatomical dead space?

• A. Air that is exchanged in alveoli
• B. Air that is exhaled without gas exchange
• C. Air trapped in the small airways
• D. Air that engages in gas exchange

Answer: (B)

Anatomical dead space refers to the volume of air that enters the respiratory system but does not participate in gas exchange. This includes the air in the conducting airways such as the trachea, bronchi, and bronchioles, where no alveoli are present for the exchange of oxygen and carbon dioxide. When air is inhaled, it travels through these airways before reaching the alveoli, where actual gas exchange occurs.

When the air is exhaled, it includes both the air that was involved in gas exchange in the alveoli and the air that passed through the dead space. Since the air in the anatomical dead space does not reach the alveoli, it does not contribute to the body's oxygenation or carbon dioxide removal. Therefore, the description that focuses on air exhaled without gas exchange accurately captures the nature of anatomical dead space.