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The carotid body is a small cluster of chemoreceptors and supporting cells located near the bifurcation of the carotid artery. It measures changes in blood pressure and the composition of arterial blood flowing past it, including the partial pressures of oxygen and carbon dioxide and is also sensitive to changes in pH and temperature. The chemoreceptors responsible for sensing changes in blood gasses are called glomus cells. While the central chemoreceptors in the brainstem are highly sensitive to CO2, the carotid body is a peripheral chemoreceptor that provides afferent input to the respiratory center that is highly O2 dependent. Below an oxygen partial pressure of 60 torr, the carotid body cells release dopamine and trigger EPSP's in synapsed neurons leading to the respiratory center. This event is mediated by a unique potassium channel that is responsive to the partial pressure of O2. The peripheral chemoreceptor's input is secondary to CO2 sensitive cells in the central chemoreceptors in healthy patients, but is the primary driver of ventilation in individuals who suffer from chronic hypercapnia (as in emphysema).
It gives feedback to the medulla oblongata via the afferent branches of the glossopharyngeal nerve (IX). The medulla, in turn, regulates breathing and blood pressure.
Disorders
A paraganglioma is a tumor that may involve the carotid body.
How they work
The type 1 gloumus cells in the carotid (and aortic bodies) have hypoxia dependent K+ channels which close upon hypoxia. This creates a relative depolarisation and stimulates the afferent nerve fibres (CN IX in the carotid) to fire an action potential to the nucleus of the tractus solitarius.
See also
External links
"Carotid body"