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
The primary direct stimulus for excitation of central chemoreceptors regulating ventilation is 
Select and explain. 
A. Increased H+, B. Increased CO2, C. Increased O2, D. Decreased CO2
A: Increased H+
Answer: A: Increased H+ 
Explanation: The main chemoreceptors involved in respiratory feedback are: Central chemoreceptors: These are located on the ventrolateral surface of medulla oblongata and detect changes in the pH of spinal fluid. Ref: guyton and hall textbook of medical physiology 12 edition page number:371,372,373