Corpus: Carotid body

The carotid body is a parasympathetic paraganglion localized within the carotid bifurcation, measuring about 5 millimetres in size.

The functional cells of the carotid body are located within a connective tissue sheath and are in contact with the intravascular space of the carotid bifurcation. They are called type I glomus cells. These cells function as peripheral chemoreceptors of respiratory regulation. They respond to decreases in partial pressure of oxygen (pO₂), increases in the partial pressure of carbon dioxide (pCO₂) and decreases in blood pH (acidosis) by releasing transmitters. Changes in pO₂ appear to have the strongest influence. The subsequent excitation of afferent fibers of the glossopharyngeal nerve leads to an increase in the central respiratory drive.

Hypoxia in the carotid body cells decreases mitochondrial activity, which increases cellular AMP levels. AMP activates the AMP-dependent kinase, which causes depolarisation by inhibiting potassium channels (so-called TASK channels, short for Two-pore-domain Acid Sensitive K-channels). During depolarisation, a calcium influx causes the release of dopamine into the synaptic cleft. Hypercapnia and acidosis enhance the depolarisation. The signal is transmitted to the dorsal respiratory group (DRG) in the medulla oblongata via the corresponding cranial nerve.