Editing Coronary circulation (section)

==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}}