Chemoreceptors

Chemoreceptors are specialized sensory receptors that detect chemical stimuli and translate them into neural signals. They monitor the chemical composition of the external environment and internal fluids, and influence reflexes and homeostatic responses that regulate respiration, circulation, digestion, and perception.

There are two broad groups: peripheral chemoreceptors and central chemoreceptors. Peripheral chemoreceptors are located in the carotid bodies at the bifurcation of the common carotid arteries and in the aortic bodies along the aorta. They primarily sense arterial blood oxygen, carbon dioxide, and pH (via hydrogen ion concentration) and relay signals through the glossopharyngeal (carotid) and vagus (aortic) nerves to the brainstem. Central chemoreceptors lie within the brainstem, particularly the medulla, and respond to changes in the pH of the cerebrospinal fluid, which reflect CO2 levels in the blood because CO2 crosses the blood-brain barrier. They modulate ventilation to maintain stable arterial gas values.

In addition to respiratory control, chemoreceptors are integrated into the senses of taste and smell. Taste receptor cells in taste buds respond to ionic and molecular stimuli corresponding to sweet, sour, salty, bitter, and umami. Olfactory receptor neurons in the nasal epithelium detect a broad array of volatile chemicals via G-protein–coupled receptors, linking odor detection to perception.

Signal transmission from chemoreceptors typically involves neurotransmitter release that excites or inhibits afferent neurons, leading to adjusted breathing patterns, heart rate, and hormonal responses as needed. Dysfunction or altered sensitivity of chemoreceptors can contribute to respiratory disorders, impaired hypoxic or hypercapnic responses, and related clinical conditions.