A glomus cell (type I) is a peripheral chemoreceptor, mainly located in the carotid bodies and aortic bodies, that helps the body regulate breathing. When there is a decrease in the blood's pH, a decrease in oxygen (pO2), or an increase in carbon dioxide (pCO2), the carotid bodies and the aortic bodies signal the medulla oblongata (specifically the dorsal inspiratory center in the medulla oblongata) to increase the volume and rate of breathing. The glomus cells have a high metabolic rate and good blood perfusion and thus are sensitive to changes in arterial blood gas tension. Glomus cells are very similar structurally to neurons, and they are indeed derived from the neural crest, while type II glomus cells are sustentacular cells having a similar function to neuroglia.
Autonomic ganglia innervate the glomus cells, and some presynaptic sympathetic ganglia synapse with glomus cells. The nerve fibers pick up the signals sent by glomus cells and transmit them to the central nervous system for treatment. The signalling within the chemoreceptors is thought to be mediated by the release of neurotransmitters by the glomus cells, including dopamine, noradrenaline, acetylcholine, substance P, vasoactive intestinal peptide and enkephalins. Vasopressin has been found to inhibit the response of glomus cells to hypoxia, presumably because the usual response to hypoxia is vasodilatation, which in case of hypovolemia should be avoided. Furthermore, glomus cells are highly responsive to angiotensin II through AT1 receptors, providing information about the body's fluid and electrolyte status.
Clusters of glomus cells, of which the carotid bodies and aortic bodies are the most important, are called non-chromaffin or parasympathetic paraganglia. They are also present along the vagus nerve, in the inner ears, in the lungs, and at other sites. Neoplasms of glomus cells are known as paraganglioma, among other names, they are generally non-malignant.
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