Carotid body 529895 226053795 2008-07-16T16:55:04Z 86.21.56.178 {{Infobox Anatomy | Name = {{PAGENAME}} | Latin = glomus caroticum | GraySubject = 277 | GrayPage = 1281 | Image = Gray1186.png | Caption = Section of part of human glomus caroticum. Highly magnified. Numerous bloodvessels are seen in section among the gland cells. | Image2 = Gray474.png | Caption2 = Diagram showing the origins of the main branches of the carotid arteries. | Precursor = | System = | Artery = | Vein = | Nerve = | Lymph = | MeshName = | MeshNumber = | DorlandsPre = g_07 | DorlandsSuf = 12394794 | }} The '''carotid body''' ([[carotid glomus]] or [[glomus caroticum]]) is a small cluster of [[chemoreceptor]]s and supporting cells located near the fork ([[bifurcation]]) of the [[carotid artery]] (which runs along both sides of the throat). The carotid body detects changes in the composition of arterial blood flowing through it, mainly the partial pressure of [[oxygen]], but also of [[carbon dioxide]]. Furthermore, it is also sensitive to changes in [[pH]] and [[temperature]]. ==Composition== The carotid body is made up of two types of cell: type I (glomus) cells, and type II (sustentacular) cells. Glomus cells are derived from [[neural crest]],<ref name="pmid7938227">{{cite journal |author=Gonzalez C, Almaraz L, Obeso A, Rigual R |title=Carotid body chemoreceptors: from natural stimuli to sensory discharges |journal=Physiol. Rev. |volume=74 |issue=4 |pages=829–98 |year=1994 |pmid=7938227 |doi=}}</ref> which, in turn are derived from [[neuroectoderm]]. They release a variety of [[neurotransmitter]]s, including [[acetylcholine]], [[adenosine triphosphate|ATP]], and [[dopamine]] that trigger [[EPSP]]s in synapsed neurons leading to the respiratory center. Type II cells resemble [[Glial cell|glia]], express the glial marker S100 and act as supporting cells. ==Function== The carotid body functions as a sensor, it responds to a stimulus, primarily O<sub>2</sub> partial pressure, which is detected by the type I (glomus) cells, and triggers an [[action potential]] in an afferent nerve fiber, the carotid sinus nerve, which relays the information to the central nervous system. ===Stimulus=== While the central chemoreceptors in the brainstem are highly sensitive to CO<sub>2</sub> the carotid body is a peripheral chemoreceptor that mainly provides afferent input to the respiratory center that is highly O<sub>2</sub> dependent. However, the carotid body also senses increases in CO<sub>2</sub> partial pressure and decreases in arterial pH, but to a lesser degree than for O<sub>2</sub> The output of the carotid bodies is low at an oxygen [[partial pressure]] above about 100 mmHg ([[torr]]) (at normal physiological pH), but below this the activity of the type I (glomus) cells increases rapidly. ===Detection=== The mechanism for detecting reductions in P<small>O<sub>2</sub></small> is not well understood. There may be a [[heme]]-containing protein in the glomus cell which responds to the loss of [[Complex (chemistry)|complexed]] oxygen by reducing the probability of potassium channels being open. Another possibility is that low P<small>O<sub>2</sub></small> inhibits [[NADPH oxidase]] in mitochondria. This would increase the ratio of reduced glutathione to oxidised glutathione, which blocks potassium channels. An increased P<small>CO<sub>2</sub></small> is detected because the CO<sub>2</sub> [[diffusion|diffuses]] into the cell, where it increase the concentration of [[carbonic acid]] and thus [[protons]]. These protons displace calcium from [[BK channel|high-conductance calcium channels]], reducing potassium current. Arterial [[acidosis]] (either [[metabolic acidosis|metabolic]] or from altered [[respiratory acidosis|P<small>CO<sub>2</sub></small>]]) inhibits acid-base transporters (e.g. Na<sup>+</sup>-H<sup>+</sup>) which raise intracellular pH, and activates transporters (e.g. Cl<sup>-</sup>-HCO<sub>3</sub><sup>-</sup>) which decrease it. Changes in proton concentration caused by acidosis (or the opposite from [[alkalosis]]) inside the cell stimulates the same pathways involved in P<small>CO<sub>2</sub></small> sensing. ===Action potential=== The type 1 (glomus) cells in the carotid (and aortic bodies) are derived from neuroectoderm and are thus electrically excitable. A decrease in oxygen partial pressure, an increase in carbon dioxide partial pressure, and a decrease in arterial pH can all cause [[depolarization]] of the [[cell membrane]], and they effect this by blocking [[potassium]] currents. This reduction in the [[membrane potential]] opens [[voltage-gated]] [[calcium]] channels, which causes a rise in intracellular calcium concentration. This causes [[exocytosis]] of [[vesicles]] containing a variety of [[neurotransmitters]], including [[acetylcholine]], [[noradrenaline]], [[dopamine]], [[adenosine]], [[ATP]], [[substance P]], and [[met-enkephalin]]. These act on [[Receptor (biochemistry)|receptors]] on the afferent nerve fibres which lie in apposition to the glomus cell to cause an action potential. ===Relay=== The feedback from the carotid body is sent to the cardiorespiratory centers in the [[medulla oblongata]] via the afferent branches of the [[glossopharyngeal nerve]] . The cell bodies of this nerve are located in the petrosal ganglion. The afferent fibres of the aortic body chemoreceptors are relayed by the [[vagus nerve]]. These centers, in turn, regulate breathing and blood pressure. ==Disorders== A [[paraganglioma]] is a tumor that may involve the carotid body. ==References== <references/> ==See also== * [[Aortic body]] * [[Peripheral chemoreceptors]] ==External links== *[http://www.ursa.kcom.edu/Department/LectureNotes/Summer/ContRespiration.doc Respiratory physiology notes] at [[Kirksville College of Osteopathic Medicine]] * {{eMedicineDictionary|Carotid+body}} [[Category:Cardiovascular system]] [[Category:Respiration]] {{respiratory-stub}} [[de:Glomus caroticum]] [[mk:Каротидно тело]] [[ja:頚動脈小体]] [[pl:Kłębek szyjny]]