This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System Pa 2, Subject name: Physiology
Concerning the ventilatory response to hypoxia, TRUE is: 
Select and explain. 
A. It is the major stimulus to ventilation at high altitude, B. It is primarily brought about by the central chemoreceptors, C. It is reduced if the PCO2 is also raised, D. It rarely stimulates ventilation in patients with chronic lung disease
A: It is the major stimulus to ventilation at high altitude
Answer: A: It is the major stimulus to ventilation at high altitude 
Explanation: Ventilation increases greatly at high altitude in response to hypoxic stimulation of chemoreceptors. The other choices are incorrect : It is the peripheral chemoreceptors, not the central chemoreceptors that are responsible for the response. The response is increased if the pCO2 is also raised. Hypoxic stimulation is often impoant in patients with longstanding severe lung disease who have nearly normal values for the pH of the CSF and blood. Mild carbon monoxide poisoning is associated with a normal aerial pO2 , and therefore, there is no stimulation of the peripheral chemoreceptors.