Sensory receptors that respond to chemical stimuli in the environment or within the body, playing a key role in detecting changes in blood pH, carbon dioxide, and oxygen levels.

• A. Chemoreceptors
• B. Alpha 1 receptors
• C. Beta-agonists
• D. Smooth muscle

Answer: (A)

Chemoreceptors are the sensors that respond to chemical stimuli in the environment or the body and are essential for detecting changes in blood pH, carbon dioxide, and oxygen levels. Central chemoreceptors in the brainstem monitor hydrogen ion concentration in cerebrospinal fluid, which reflects CO2 levels in the blood, while peripheral chemoreceptors in the carotid and aortic bodies detect arterial O2, CO2, and pH and help adjust breathing accordingly. This system maintains proper acid-base balance and ensures tissues receive enough oxygen by modulating respiratory drive in response to those chemical signals. The other options don’t fit because they’re not sensory receptors: alpha-1 receptors mediate vasoconstriction, beta-agonists are drugs that stimulate beta receptors, and smooth muscle is the tissue that contracts rather than a sensor of chemical changes.