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
Intrapleural pressure is 
Select and explain. 
A. Transpulmonary pressure + Alveolar pressure, B. Transpulmonary pressure - Alveolar pressure, C. Transmural pressure + Alveolar pressure, D. Alveolar pressure - Transpulmonary pressure
D: Alveolar pressure - Transpulmonary pressure
Answer: D: Alveolar pressure - Transpulmonary pressure 
Explanation: In physiology, intrapleural pressure (also called intrathoracic pressure) refers to the pressure within the pleural cavity. Normally, the pressure within the pleural cavity is slightly less than the atmospheric pressure, in what is known as negative pressure Ref: guyton and hall textbook of medical physiology 12 edition page number: 316,317,318