Final answer:
Central chemoreceptors are sensitive because they regulate breathing by monitoring blood levels of CO2 and H+ ions, which affect the pH. An increase in CO2 triggers these receptors to stimulate the respiratory system to increase breathing rate and depth. This system helps maintain stable pH levels in the brain and blood.
Step-by-step explanation:
Central chemoreceptors are extremely sensitive because they play a critical role in maintaining homeostasis by regulating the respiratory rate based on the concentration of carbon dioxide (CO2) in the blood. These receptors, located in the medulla oblongata and brainstem, detect changes in the levels of CO2 and hydrogen ions (H+). An increase in CO2 leads to an increase in H+ due to carbonic acid formation, which decreases the pH of the cerebrospinal fluid. This triggers the central chemoreceptors to send signals to the respiratory centers, causing the rate and depth of respiration to increase, thus expelling more CO2 and consequently reducing H+ levels in the blood.
In contrast, low CO2 levels lead to shallow, slow breathing. Peripheral chemoreceptors, on the other hand, are mainly responsive to major drops in blood oxygen levels, particularly when they fall below about 60 mm Hg.
A chemoreceptor, by definition, is sensitive to chemical substances, and in the context of respiratory control, they are sensitive to CO2, H+, and sometimes lactic acid levels in the blood.