This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Physiology
Anatomical dead space is 
Select and explain. 
A. 1/3rd of tidal volume, B. 2/5th of tidal volume, C. 10 ml/kg of body weight, D. 15 ml/kg of body weight
A: 1/3rd of tidal volume
Answer: A: 1/3rd of tidal volume 
Explanation: Dead space is the volume of air that is inhaled that does not take pa in the gas exchange, because it either remains in the conducting airways or reaches alveoli that are not perfused or poorly perfused. In other words, not all the air in each breath is available for the exchange of oxygen and carbon dioxide Ref: guyton and hall textbook of medical physiology 12 edition page number: 324,325,326