Question

Respiratory centres are stimulated by-

• A. Oxygen
• B. Lactic acid
• C. Carbon dioxide
• D. Calcium

Hint:

The medulla responds chiefly to the gas it tries to blow off, not to oxygen.

Answer 1

The Correct Option is C

Step 1: The respiratory centre lies in the medulla and controls the rate and depth of breathing. Step 2: Its most powerful and normal stimulus is a rise in the arterial concentration of carbon dioxide, which is sensed largely through the resulting change in pH by central chemoreceptors. Step 3: When carbon dioxide rises, the centre increases ventilation, blowing off the excess gas and reducing blood acidity, so option (c) is correct. Step 4: Oxygen acts as a much weaker (hypoxic) drive through peripheral chemoreceptors, and lactic acid and calcium are not the primary normal stimuli, so they are not the best answer.