Chemoceptors

Chemoceptors, or chemoreceptors, are sensory receptors that detect chemical stimuli and translate them into neural signals. They are found throughout animals, including humans, and play key roles in respiration, metabolism, and the senses of taste and smell. In humans, chemoreception is organized into peripheral and central components.

Peripheral chemoreceptors include the gustatory receptors on the tongue, which mediate taste, and the olfactory receptors in the nasal epithelium, which mediate smell. In addition, the carotid bodies at the bifurcation of the common carotid arteries—and to a lesser extent the aortic bodies—are specialised peripheral chemoreceptors that sense changes in the chemical composition of arterial blood, especially oxygen, carbon dioxide, and pH, and send signals via the glossopharyngeal and vagus nerves to regulate ventilation.

Central chemoreceptors are located in the brainstem and sense the pH of the cerebrospinal fluid, which reflects CO2 levels. They adjust respiratory drive by signaling to the respiratory centers. Transduction mechanisms vary by modality: taste receptors include the T1R and T2R families; olfactory receptors are odorant-activated G-protein coupled receptors; glomus cells in carotid bodies release neurotransmitters in response to hypoxemia and hypercapnia, with afferent signals carried to the brainstem; central chemoreceptors respond primarily to hydrogen ion concentration in CSF.

Functions extend beyond detection to reflex regulation of breathing and blood gas homeostasis, as well as contributions to flavor perception, appetite, and digestion. Clinically, chemoreceptor function can be altered in disease: increased peripheral chemoreceptor sensitivity in chronic lung disease, or impaired central chemoreception in certain neurological disorders, with consequences for respiratory control.