Editing Coronary circulation

{{Short description|Circulation of blood in the blood vessels of the heart muscle (myocardium)}}
{{Infobox anatomy
| Name        = Coronary circulation
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| Width       = 379
| Image       = 2005 Surface Anatomy of the Heart.jpg
| Caption     = [[Blood vessel]]s of the coronary circulation of the human heart viewed from the front and from behind
| Nerve       =
| Action      =
| Precursor   =
}}
'''Coronary circulation''' is the [[Circulatory system#Coronary vessels|circulation of blood]] in the [[arteries]] and [[vein]]s that supply the [[cardiac muscle|heart muscle]] (myocardium).
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[[Coronary arteries]] supply [[oxygen saturation (medicine)|oxygenated]] blood to the heart muscle. [[#Cardiac veins|Cardiac veins]] then drain away the blood after it has been deoxygenated.
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Because the rest of the body, and most especially the [[brain]], needs a steady supply of oxygenated blood that is free of all but the slightest interruptions, the heart is required to function continuously. Therefore its circulation is of major importance not only to its own tissues but to the entire body and even the [[level of consciousness]] of the brain from moment to moment.
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Interruptions of coronary circulation quickly cause heart attacks ([[myocardial infarction]]s), in which the heart muscle is damaged by [[hypoxia (medical)|oxygen starvation]]. Such interruptions are usually caused by [[coronary ischemia]] linked to [[coronary artery disease]], and sometimes to [[embolism]] from other causes like obstruction in blood flow through vessels.

==Structure==
===Coronary arteries===
[[File:Coronary arteries.svg|thumb|[[Coronary arteries]] labeled in red text and other landmarks in blue text]]
[[File:Cardiac vessels.svg|thumb|Schematic view of the heart]]
[[Coronary arteries]] supply blood to the myocardium and other components of the heart. Two coronary arteries originate from the left side of the heart at the beginning (root) [[left ventricle]]. There are three [[aortic sinus]]es (dilations) in the wall of the aorta just superior to the aortic semilunar valve. Two of these, the [[aortic sinus|left posterior aortic sinus]] and [[aortic sinus|anterior aortic sinus]], give rise to the [[left coronary artery|left]] and [[right coronary arteries]], respectively. The third sinus, the [[aortic sinus|right posterior aortic sinus]], typically does not give rise to a vessel. Coronary vessel branches that remain on the surface of the heart and follow the sulci of the heart are called ''epicardial'' coronary arteries.<ref name="CNX2014">{{cite book|last1=Betts|first1=J. Gordon|title=Anatomy & physiology|date=2013|isbn=978-1938168130|url=http://cnx.org/content/m46676/latest/?collection=col11496/latest|access-date=11 August 2014|pages=787–846}}</ref>

The left coronary artery distributes blood to the left side of the heart, the left atrium and ventricle, and the interventricular septum. The [[circumflex branch of left coronary artery|circumflex artery]] arises from the left coronary artery and follows the [[coronary sulcus]] to the left. Eventually, it will fuse with the small branches of the right coronary artery. The larger [[left anterior descending artery]] (LAD), is the second major branch arising from the left coronary artery. It follows the anterior interventricular sulcus around the pulmonary trunk. Along the way it gives rise to numerous smaller branches that interconnect with the branches of the [[posterior interventricular artery]], forming [[anastomoses]]. An anastomosis is an area where vessels unite to form interconnections that normally allow blood to circulate to a region even if there may be partial blockage in another branch. The anastomoses in the heart are very small. Therefore, this ability is somewhat restricted in the heart so a [[coronary artery blockage]] often results in [[myocardial infarction]] causing [[necrosis|death of the cell]]s supplied by the particular vessel.<ref name="CNX2014"/>

The right coronary artery proceeds along the coronary sulcus and distributes blood to the right atrium, portions of both ventricles, and the [[heart conduction system]]. Normally, one or more [[Right marginal branch of right coronary artery|marginal arteries]] arise from the right coronary artery inferior to the right atrium. The marginal arteries supply blood to the superficial portions of the right ventricle. On the posterior surface of the heart, the right coronary artery gives rise to the posterior interventricular artery, also known as the posterior descending artery. It runs along the posterior portion of the interventricular sulcus toward the apex of the heart, giving rise to branches that supply the interventricular septum and portions of both ventricles.<ref name="CNX2014"/>

===Cardiac veins===
[[File:Gray491.png|thumb|Base and diaphragmatic surface of heart showing some cardiac veins]]
The [[blood vessel|vessels]] that remove the deoxygenated [[blood]] from the [[heart]] muscle are the cardiac [[vein]]s. These include the [[great cardiac vein]], the [[middle cardiac vein]], the [[small cardiac vein]], the [[smallest cardiac veins]], and the [[anterior cardiac veins]]. Cardiac veins carry blood with a poor level of [[oxygen]], from the [[myocardium]] to the [[right atrium]]. Most of the blood of the coronary veins returns through the [[coronary sinus]]. The [[anatomy]] of the veins of the heart is very variable, but generally it is formed by the following veins: heart veins that go into the coronary sinus: the [[great cardiac vein]], the [[middle cardiac vein]], the [[small cardiac vein]], the posterior vein of the [[left ventricle]], and the [[Oblique vein of the left atrium|oblique vein of Marshall]]. Heart veins that go directly to the right atrium: the anterior cardiac veins, the [[smallest cardiac veins]] (Thebesian veins).<ref>[http://radiopaedia.org/articles/coronary-veins  www.radiopaedia.org/]</ref>

===Anastomoses===
[[File:Coronary Arteries.tif|thumb|Cast of coronary arteries (right = yellow, left = red)]]
There are some anastomoses between branches of the two coronary arteries.  However the coronary arteries are functionally end arteries and so these meetings are referred to as potential [[anastomoses]], which lack function, as opposed to true anastomoses like that in the palm of the hand. This is because blockage of one coronary artery generally results in death of the heart tissue due to lack of sufficient blood supply from the other branch. When two arteries or their branches join, the area of the myocardium receives dual blood supply. These junctions are called anastomoses. If one coronary artery is obstructed by an [[atheroma]], the second artery is still able to supply oxygenated blood to the myocardium. However, this can only occur if the atheroma progresses slowly, giving the anastomoses a chance to proliferate.{{citation needed|date=April 2021}}

Under the most common configuration of coronary arteries, there are three areas of anastomoses. Small branches of the LAD (left anterior descending/anterior interventricular) branch of the left coronary join with branches of the posterior interventricular branch of the right coronary in the interventricular sulcus (groove). More superiorly, there is an anastomosis between the circumflex artery (a branch of the left coronary artery) and the right coronary artery in the atrioventricular groove. There is also an anastomosis between the septal branches of the two coronary arteries in the interventricular septum. The photograph shows area of heart supplied by the right and the left coronary arteries.{{citation needed|date=April 2021}}

===Variation===
The left and right coronary arteries occasionally arise by a common trunk, or their number may be increased to three; the additional branch being the posterior coronary artery (which is smaller in size). In rare cases, a person will have the third coronary artery run around the root of the aorta.{{citation needed|date=April 2021}}

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).{{citation needed|date=April 2021}}

====Coronary artery dominance====
The artery that supplies the posterior third of the [[interventricular septum]] – the [[posterior descending artery]] (PDA)<ref>{{Chorus|00460}}</ref> determines the coronary dominance.<ref name="Hurst">{{cite book | last=Fuster | first=V |author2=Alexander RW|author3=O'Rourke RA | title=Hurst's The Heart | publisher=McGraw-Hill | year=2001 | page=53 | edition=10th | isbn=0-07-135694-0 }}</ref>
* If the posterior descending artery is supplied by the [[right coronary artery]] (RCA), then the coronary circulation can be classified as "right-dominant."
* If the posterior descending artery is supplied by the [[circumflex branch of left coronary artery|circumflex artery]] (CX), a branch of the left artery, then the coronary circulation can be classified as "left-dominant."
* If the posterior descending artery is supplied by both the right coronary artery and the circumflex artery, then the coronary circulation can be classified as "co-dominant."

Approximately 70% of the general population are right-dominant, 20% are co-dominant, and 10% are left-dominant.<ref name="Hurst"/>
A precise anatomic definition of dominance would be the artery which gives off supply to the AV node i.e. the AV nodal artery. Most of the time this is the right coronary artery.{{citation needed|date=April 2021}}

==Function==

===Supply to papillary muscles===
The [[papillary muscle]]s attach 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 may leak 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]].  Similarly, the leaking of blood from the right ventricle through the tricuspid valve and into the right atrium can also occur, and this is described as [[tricuspid insufficiency]] or tricuspid regurgitation.{{citation needed|date=April 2021}}

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 |vauthors=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=1714–1718 |year=1995 |pmid=7882478 |doi=10.1161/01.cir.91.6.1714}}</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.{{citation needed|date=April 2021}}

===Changes in diastole===
During contraction of the [[ventricle (heart)|ventricular]] myocardium ([[Systole (medicine)|systole]]), the subendocardial coronary vessels (the vessels that enter the myocardium) are compressed due to the high ventricular pressures.
This compression results in momentary retrograde blood flow (i.e., blood flows backward toward the aorta) which further inhibits perfusion of myocardium during systole.
However, the epicardial coronary vessels (the vessels that run along the outer surface of the heart) remain open.
Because of this, blood flow in the subendocardium stops during ventricular contraction.
As a result, most myocardial perfusion occurs during heart relaxation ([[diastole]]) when the subendocardial coronary vessels are open and under lower pressure.
Flow never comes to zero in the right coronary artery, since the right ventricular pressure is less than the diastolic blood pressure.<ref>{{cite journal |last1=Algranati |first1=Dotan |last2=Kassab |first2=Ghassan S |last3=Lanir |first3=Yoram |title=Mechanisms of myocardium-coronary vessel interaction |journal=Am J Physiol Heart Circ Physiol |date=March 2010 |volume=298 |issue=3 |page=H861–873 |doi=10.1152/ajpheart.00925.2009 |pmid=19966048 |url=https://journals.physiology.org/doi/pdf/10.1152/ajpheart.00925.2009 |access-date=26 May 2021|pmc=2838558 }}</ref>

===Changes in oxygen demand===
The heart regulates the amount of [[vasodilation]] or vasoconstriction of the coronary arteries based upon the oxygen requirements of the heart. This contributes to the filling difficulties of the coronary arteries.
Compression remains the same. Failure of oxygen delivery caused by a decrease in blood flow in front of increased oxygen demand of the heart results in tissue [[ischemia]], a condition of oxygen deficiency. Brief ischemia is associated with intense chest pain, known as [[Angina pectoris|angina]]. Severe ischemia can cause the heart muscle to die from hypoxia, such as during a [[myocardial infarction]].  Chronic moderate ischemia causes contraction of the heart to weaken, known as myocardial hibernation.{{citation needed|date=April 2021}}

In addition to metabolism, the coronary circulation possesses unique pharmacologic characteristics. Prominent among these is its reactivity to adrenergic stimulation.{{citation needed|date=April 2021}}

==Branches==
The following are the named branches of the coronary circulation in a right-dominant heart:{{citation needed|date=April 2021}}
* [[Aorta]]
** [[Left coronary artery]] / Left main coronary artery (LMCA)
*** [[Left circumflex artery]] (LCX)
**** [[Obtuse marginal artery]] #1 (OM1)
**** [[Obtuse marginal artery]] #2 (OM2)
*** [[Left anterior descending artery]] (LAD)
**** [[Diagonal artery]] #1
**** [[Diagonal artery]] #2
** [[Right coronary artery]] (RCA)
*** [[Atrioventricular nodal branch]]
*** [[Right marginal artery]]
*** [[Posterior descending artery]] (PDA)
*** [[Posteriolateral artery]] #1 (PL#1)
*** [[Posteriolateral artery]] #2 (PL#2)

== Clinical significance ==
The [[blood vessel|vessels]] that deliver [[oxygen]]-rich [[blood]] to the [[myocardium]] are the [[coronary arteries]]. When the [[artery|arteries]] are healthy, they are capable of autoregulating themselves to maintain the coronary blood flow at levels appropriate to the needs of the [[myocardium|heart muscle]]. 

The relatively narrow coronary arteries are commonly affected by [[atherosclerosis]] and can become blocked, causing [[Angina pectoris|angina]] or a [[myocardial infarction|heart attack]]. The coronary arteries are classified as "terminal circulation", since they represent the only source of blood supply to the myocardium; there is very little redundant blood supply, that is why blockage of these vessels can be so critical.{{citation needed|date=April 2021}}

==Additional images==
<gallery>
 File:Blausen 0260 CoronaryVessels Anterior.png|Anterior view of coronary circulation
 File:Blausen 0261 CoronaryVessels Posterior.png|Posterior view of coronary circulation
 File:Blausen 0256 CoronaryArteries 02.png|Illustration of coronary arteries

 </gallery>

==See also==
* [[Anomalous aortic origin of a coronary artery]]
* [[Cardiac skeleton]]
* [[Coronary sinus]]
* [[Coronary steal]]
* [[Cardiology]]
* [[Left coronary artery]]
* [[Right coronary artery]]

==References==
{{CNX A&P}}
{{commons category|Coronary vessels|Coronary circulation}}
{{Reflist}}

{{Heart anatomy|state=collapsed}}

{{Authority control}}

{{DEFAULTSORT:Coronary Circulation}}
[[Category:Cardiac anatomy]]
[[Category:Cardiology]]
[[Category:Arteries]]