| Coronary circulation | |
|---|---|
 Blood vessels of the coronary circulation of the human heart viewed from the front and from behind | |
| Identifiers | |
| MeSH | D003326 |
| Anatomical terminology | |
Coronary circulation is thecirculation of blood in thearteries andveins that supply theheart muscle (myocardium).Coronary arteries supplyoxygenated blood to the heart muscle.Cardiac veins then drain away the blood after it has been deoxygenated.Because the rest of the body, and most especially thebrain, 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 thelevel of consciousness of the brain from moment to moment.Interruptions of coronary circulation quickly cause heart attacks (myocardial infarctions), in which the heart muscle is damaged byoxygen starvation. Such interruptions are usually caused bycoronary ischemia linked tocoronary artery disease, and sometimes toembolism from other causes like obstruction in blood flow through vessels.
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 threeaortic sinuses (dilations) in the wall of the aorta just superior to the aortic semilunar valve. Two of these, theleft posterior aortic sinus andanterior aortic sinus, give rise to theleft andright coronary arteries, respectively. The third sinus, theright 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 calledepicardial coronary arteries.[1]
The left coronary artery distributes blood to the left side of the heart, the left atrium and ventricle, and the interventricular septum. Thecircumflex artery arises from the left coronary artery and follows thecoronary sulcus to the left. Eventually, it will fuse with the small branches of the right coronary artery. The largerleft 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 theposterior interventricular artery, forminganastomoses. 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 acoronary artery blockage often results inmyocardial infarction causingdeath of the cells supplied by the particular vessel.[1]
The right coronary artery proceeds along the coronary sulcus and distributes blood to the right atrium, portions of both ventricles, and theheart conduction system. Normally, one or moremarginal 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.[1]
Thevessels that remove the deoxygenatedblood from theheart muscle are the cardiacveins. These include thegreat cardiac vein, themiddle cardiac vein, thesmall cardiac vein, thesmallest cardiac veins, and theanterior cardiac veins. Cardiac veins carry blood with a poor level ofoxygen, from themyocardium to theright atrium. Most of the blood of the coronary veins returns through thecoronary sinus. Theanatomy 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: thegreat cardiac vein, themiddle cardiac vein, thesmall cardiac vein, the posterior vein of theleft ventricle, and theoblique vein of Marshall. Heart veins that go directly to the right atrium: the anterior cardiac veins, thesmallest cardiac veins (Thebesian veins).[2]
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 potentialanastomoses, 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 anatheroma, 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]
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]
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]
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]
The artery that supplies the posterior third of theinterventricular septum – theposterior descending artery (PDA)[3] determines the coronary dominance.[4]
Approximately 70% of the general population are right-dominant, 20% are co-dominant, and 10% are left-dominant.[4]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]
Thepapillary muscles attach themitral valve (the valve between theleft atrium and theleft ventricle) and thetricuspid valve (the valve between theright atrium and theright 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 asmitral 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 astricuspid insufficiency or tricuspid regurgitation.[5]
The anterolateral papillary muscle more frequently receives two blood supplies:left anterior descending (LAD) artery and theleft circumflex artery (LCX).[6]It is therefore more frequently resistant tocoronary ischemia (insufficiency of oxygen-rich blood). On the other hand, the posteromedial papillary muscle is usually supplied only by the PDA.[6] This makes the posteromedial papillary muscle significantly more susceptible toischemia. The clinical significance of this is that amyocardial infarction involving the PDA is more likely to cause mitral regurgitation.[citation needed]
During contraction of theventricular myocardium (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.[7]
The heart regulates the amount ofvasodilation 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 tissueischemia, a condition of oxygen deficiency. Brief ischemia is associated with intense chest pain, known asangina. Severe ischemia can cause the heart muscle to die from hypoxia, such as during amyocardial infarction. Chronic moderate ischemia causes contraction of the heart to weaken, known as myocardial hibernation.[citation needed]
In addition to metabolism, the coronary circulation possesses unique pharmacologic characteristics. Prominent among these is its reactivity to adrenergic stimulation.[citation needed]
The following are the named branches of the coronary circulation in a right-dominant heart:[citation needed]
Thevessels that deliveroxygen-richblood to themyocardium are thecoronary arteries. When thearteries are healthy, they are capable of autoregulating themselves to maintain the coronary blood flow at levels appropriate to the needs of theheart muscle.
The relatively narrow coronary arteries are commonly affected byatherosclerosis and can become blocked, causingangina or aheart 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]
This article incorporates text from theCC BY book:OpenStax College, Anatomy & Physiology. OpenStax CNX. 30 July 2014.
