When central chemoreceptors sense an increase in PCO2 and hydrogen ions, what physiological response occurs?

• A. Hypopnea
• B. Apnea
• C. Hyperpnea
• D. Bradypnea

Answer: (C)

When central chemoreceptors in the medulla oblongata detect an increase in carbon dioxide (PCO2) and hydrogen ions (H+), the physiological response that occurs is hyperpnea. This response is characterized by an increase in the depth and rate of breathing.

The central chemoreceptors are highly sensitive to changes in the levels of PCO2 in the blood. When PCO2 levels rise, it leads to an increase in hydrogen ion concentration, causing a drop in pH (acidosis). In response to this condition, the body stimulates an increase in ventilation to expel the excess carbon dioxide, thereby normalizing blood gas levels and pH. This result is hyperpnea, which helps restore homeostasis by facilitating gas exchange and reducing CO2 levels in the blood.

The other options refer to alterations in respiratory patterns that are not direct responses to increased PCO2 and hydrogen ions. Hypopnea indicates a decrease in the rate and depth of breathing, apnea refers to a temporary cessation of breathing, and bradypnea describes slowed breathing. All of these conditions would not effectively address the physiological need to remove excess CO2, which is why they are not the correct responses to the detected increases in PCO2 and