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
[{'content': 'Negative intrapleural pressure is due to? \nSelect and explain. \nA. Lymphatic drainage from plural cavity, B. Equally distributed surfactant, C. Negative pressure in alveoli, D. Presence of cartilaginous ring at the upper airway', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A. Lymphatic drainage from plural cavityPleural cavity is a closed cavity. And the pressure is always negative due to the following factors:a. The lungs have a tendency to recoil inwards, therefore visceral pleura is pulled inwards.b. Surface tension also help by creating an inward force in alveoli.c. The thorax has a tendency to recoil outwards, pulling parietal pleura with it. Therefore, the pleural cavity is stretched on both sides leading to increase in its volume and decrease pressure inside. And it becomes negative.d. Also there is a continuous Lymphatic drainage from pleural cavity, which creates a suction force in pleural cavity, keeping the pressure negative.e. Note: Surfactant by decreasing Surface tension actually opposes the negative pressure.f. And pressure in alveoli is same as atmospheric pressure, taken as ZERO.', 'role': 'assistant'}]