• Chemoreceptors are cells which can sense and respond to the concentration of chemicals in the surrounding extracellular fluid. Several anatomical collections of chemoreceptors exist throughout the body and can sense changes in the partial pressures of arterial oxygen and carbon dioxide as well as shifts in the blood pH. Sensory output from the chemoreceptors travels to the brainstem respiratory centers and represents the afferent limb of a negative feedback control circuit which helps maintain constant partial pressures of arterial carbon dioxide and oxygen as described in integrated respiratory control.