Coronary circulation
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{{Infobox Anatomy |
Name = Coronary circulation |
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Image = Gray492.png |
Caption = An anterior view of the [[heart]] shows the [[right coronary artery]] and the anterior descending branch of the [[left coronary artery]]. |
Image2 = Gray491.png |
Caption2 = Base and diaphragmatic surface of heart. |
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MeshName = Coronary+Vessels |
MeshNumber = A07.231.114.269 |
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'''Coronary circulation''' is the circulation of blood in the [[blood vessel]]s that supply [[blood]] to and from the [[heart]] muscle itself. Although blood fills the chambers of the heart, the muscle tissue of the heart, or [[myocardium]], is so thick that it requires coronary blood vessels to deliver blood deep into it. The vessels that deliver oxygen-rich blood to the myocardium are known as coronary arteries. The vessels that remove the deoxygenated blood from the heart muscle are known as [[cardiac veins]].
The coronary
[[artery|arteries]] that run on the surface of the heart are called epicardial coronary arteries. These arteries, when healthy, are capable of autoregulation to maintain coronary blood flow at levels appropriate to the needs of the [[myocardium|heart muscle]]. These relatively narrow vessels are commonly affected by [[atherosclerosis]] and can become blocked, causing [[Angina pectoris|angina]] or a [[myocardial infarction|heart attack]]. (See also: [[circulatory system]].) The coronary arteries that run deep within the myocardium are referred to as subendocardial.
The coronary arteries are classified as "end circulation", since they represent the only source of blood supply to the myocardium: there is very little redundant blood supply, which is why blockage of these vessels can be so critical.
==Coronary anatomy==
[[Image:Cardiac vessels.png|right|300px|thumb|Schematic view of the heart vessels]]
[[Image:Aortic stenosis rheumatic, gross pathology 20G0014 lores.jpg|thumb|300px|The coronary arteries' ostia and their proximal segments. The proximal portion of [[right coronary artery]] and its [[ostium]] can be seen at the lower left (of the image). The [[left main coronary artery]] and its ostium are seen on the right (of the image). An [[aortic valve]] that, due to [[rheumatic heart disease]], has a severe [[aortic stenosis|stenosis]] is seen at the centre (of the image). The [[pulmonary trunk]] is seen at the lower right (of the image). [[Autopsy]] specimen.]]
The exact anatomy of the myocardial blood supply system varies considerably from person to person. A full evaluation of the coronary arteries requires [[cardiac catheterization]] or [[Computed tomography#Cardiac CT|CT coronary angiography]].
In general there are two main coronary arteries, the left and right.
* [[Right coronary artery]]
* [[Left coronary artery]]
Both of these arteries originate from the beginning (root) of the [[aorta]], immediately above the [[aortic valve]]. As discussed below, the left coronary artery originates from the left [[aortic sinus]], while the right coronary artery originates from the right aortic sinus.
===Variations===
Four percent of people have a third, the posterior coronary artery. In rare cases, a person will have one coronary artery that runs around the root of the aorta.
Occasionally, a coronary artery will exist as a double structure (i. e. there are two arteries, parallel to each other, where ordinarily there would be one).
===Coronary artery dominance===
The artery that supplies the [[posterior descending artery]] (PDA) and the [[posterolateral artery]] (PLA) determines the coronary dominance.
* If the [[right coronary artery]] (RCA) supplies both these arteries, the circulation can be classified as "right-dominant".
* If the [[circumflex artery]] (CX), a branch of the left artery, supplies both these arteries, the circulation can be classified as "left-dominant".
* If the RCA supplies the PDA and the CX supplies the PLA, the circulation is known as "co-dominant".
Approximately 60% of the general population are right-dominant, 25% are co-dominant, and 15% are left-dominant.<ref name="pmid15929526">{{cite journal |author=Kaimkhani ZA, Ali MM, Faruqi AM |title=Pattern of coronary arterial distribution and its relation to coronary artery diameter |journal=Journal of Ayub Medical College, Abbottabad : JAMC |volume=17 |issue=1 |pages=40–3 |year=2005 |pmid=15929526 |doi=}}</ref>
==Blood supply of the papillary muscles==
The [[papillary muscle]]s tether the [[mitral valve]] (the valve between the [[left atrium]] and the [[left ventricle]]) and the [[tricuspid valve]] (the valve between the [[right atrium]] and the [[right ventricle]]) to the wall of the heart. If the papillary muscles are not functioning properly, the mitral valve leaks during contraction of the left ventricle. This causes some of the blood to travel "in reverse", from the left ventricle to the left atrium, instead of forward to the aorta and the rest of the body. This leaking of blood to the left atrium is known as [[mitral regurgitation]].
The anterolateral papillary muscle more frequently receives two blood supplies: [[left anterior descending]] (LAD) artery and the [[left circumflex artery]] (LCX).<ref name=voci>{{cite journal |author=Voci P, Bilotta F, Caretta Q, Mercanti C, Marino B |title=Papillary muscle perfusion pattern. A hypothesis for ischemic papillary muscle dysfunction |journal=Circulation |volume=91 |issue=6 |pages=1714–8 |year=1995 |pmid=7882478 |doi=}}</ref>
It is therefore more frequently resistant to coronary [[ischemia]] (insufficiency of oxygen-rich blood). On the other hand, the posteromedial papillary muscle is usually supplied only by the PDA.<ref name=voci/> This makes the posteromedial papillary muscle significantly more susceptible to ischemia. The clinical significance of this is that a [[myocardial infarction]] involving the PDA is more likely to cause mitral regurgitation.
==Coronary flow==
During contraction of the [[ventricle (heart)|ventricular]] myocardium ([[systole]]), the subendocardial coronary vessels (the vessels that enter the myocardium) are compressed due to the high intraventricular pressures. However the epicardial coronary vessels (the vessels that run along the outer surface of the heart) remain patent. Because of this, blood flow in the subendocardium stops. As a result most myocardial perfusion occurs during heart relaxation ([[diastole]]) when the subendocardial coronary vessels are patent and under low pressure. This contributes to the filling difficulties of the coronary arteries.
Compression remains the same. Failure of oxygen delivery via increases in blood flow to meet the increased oxygen demand of the heart results in tissue ischemia, a condition of oxygen debt. Brief ischemia is associated with intense chest pain, known as [[Angina pectoris|angina]]. Severe ischemia can cause the heart muscle to die of oxygen starvation, called a [[myocardial infarction]]. Chronic moderate ischemia causes contraction of the heart to weaken, known as myocardial hibernation.
In addition to metabolism, the coronary circulation possesses unique pharmacologic characteristics. Prominent among these is its reactivity to adrenergic stimulation. The majority of vasculature in the body constricts to [[norepinephrine]], a sympathetic neurotransmitter the body uses to increase blood pressure. In the coronary circulation, [[norepinephrine]] elicits vasodilation, due to the predominance of beta-adrenergic receptors in the coronary circulation. Agonists of alpha-receptors, such as phenylephrine, elicit very little constriction in the coronary circulation.
==See also==
*[[Cardiology]]
==References==
<references/>
{{Arteries of chest}}
{{Veins of the torso}}
[[Category:Cardiovascular system]]
[[Category:Cardiac anatomy]]
[[Category:Cardiology]]
[[Category:Arteries]]
[[da:Kranspulsåre]]
[[de:Koronargefäß]]
[[es:Circulación coronaria]]
[[eu:Arteria koronario]]
[[fa:سرخرگ کرنری]]
[[fr:Artère coronaire]]
[[ko:관상동맥]]
[[it:Circolazione coronarica]]
[[la:Arteriae coronoriae]]
[[nl:Kransslagader]]
[[ja:冠動脈]]
[[no:Kransarterie]]
[[nn:Kranspulsåre]]
[[pl:Krążenie wieńcowe]]
[[pt:Circulação coronária]]
[[fi:Sepelvaltimo]]
[[sv:Kranskärl]]
[[ur:تاجی دوران]]
[[zh:冠状血管]]