Question

A rise in arterial PCO₂ triggers an increase in ventilation by stimulating both central and peripheral chemoreceptors. The response of central chemoreceptors is due to...

a) diffusion of carbon dioxide into brain extracellular fluid, which stimulates chemoreceptors directly
b) diffusion of hydrogen ions into brain extracellular fluid, which stimulates chemoreceptors directly
c) diffusion of carbon dioxide into brain extracellular fluid, which reacts with water to form hydrogen ions, which stimulate chemoreceptors directly
d) diffusion of carbon dioxide into brain extracellular fluid, which reacts with water to form bicarbonate ions, which stimulate chemoreceptors directly
e) direct stimulation by hydrogen ions in arterial blood

Answer 1

The direct response of central chemoreceptors to a rise in arterial PCO₂ is due to the diffusion of carbon dioxide into brain extracellular fluid, which forms hydrogen ions, activating the chemoreceptors to increase respiration.

Step-by-step explanation:

A rise in arterial PCO₂ triggers an increase in ventilation by stimulating both central and peripheral chemoreceptors. The response of central chemoreceptors is primarily due to diffusion of carbon dioxide into brain extracellular fluid, which reacts with water to form hydrogen ions (H+), which then stimulate chemoreceptors directly. This cascade event is influenced by the fact that carbon dioxide can readily diffuse across the blood-brain barrier and upon entering the brain extracellular fluid, it forms carbonic acid which dissociates into hydrogen ions and bicarbonate ions. It is the increase in hydrogen ions that leads to a decrease in pH and subsequently activates the central chemoreceptors. These chemoreceptors, in turn, signal the respiratory centers of the brain to increase the rate and depth of respiration, thus helping to expel more carbon dioxide and reduce the level of hydrogen ions in the blood.