The

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...

is a muscular organ situated in the

mediastinum The mediastinum (from ) is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is an undelineated region that contains a group of structures within the thorax, namely the heart and its vessels, the esophagu ...

. It consists of four chambers, four valves, two main arteries (the coronary arteries), and the conduction system. The left and right sides of the heart have different functions: the right side receives de-oxygenated blood through the

superior Superior may refer to: *Superior (hierarchy), something which is higher in a hierarchical structure of any kind Places *Superior (proposed U.S. state), an unsuccessful proposal for the Upper Peninsula of Michigan to form a separate state *Lake ...

and inferior

venae cavae In anatomy, the venae cavae (; singular: vena cava ; ) are two large veins (great vessels) that return deoxygenated blood from the body into the heart. In humans they are the superior vena cava and the inferior vena cava, and both empty into the ...

and pumps blood to the lungs through the

pulmonary artery A pulmonary artery is an artery in the pulmonary circulation that carries deoxygenated blood from the right side of the heart to the lungs. The largest pulmonary artery is the ''main pulmonary artery'' or ''pulmonary trunk'' from the heart, and t ...

, and the left side receives saturated blood from the lungs.

Heart location, orientation, and projection to the chest

The heart has the shape of a pyramid, with its apex pointing towards the left nipple while its base forms the posterior surface of the heart. Other surfaces are the anterior, inferior (or diaphragmatic), and two pulmonary surfaces facing the lungs. Its longest dimension (apical to base) is broadly 12–13 cm, while the average weight is 250 grams in females and 300 grams in males. Its primary role is to receive the blood from the body, pump it to the lungs to be oxygenated, and receive it once more to pump it again to the rest of the human body tissues. The right side of the heart (which consists of the

right atrium The atrium ( la, ātrium, , entry hall) is one of two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular valves. There are two atr ...

and the

right ventricle A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the upper ...

) receives the desaturated blood, while the left side (consisting of the

left atrium The atrium ( la, ātrium, , entry hall) is one of two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular valves. There are two atr ...

and

left ventricle A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the upper ...

) receives the oxygenated blood. The

pericardium The pericardium, also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong connective tissue (fibrous pericardium), and an inner layer made of ...

is a thick membrane that covers the heart. It consists of two layers: the fibrous pericardium and the serous pericardium. It forms two recesses: the transverse recess and oblique recess. The transverse recess lies behind the

aorta The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes ...

and

pulmonary trunk A pulmonary artery is an artery in the pulmonary circulation that carries deoxygenated blood from the right side of the heart to the lungs. The largest pulmonary artery is the ''main pulmonary artery'' or ''pulmonary trunk'' from the heart, and t ...

, while the oblique recess lies behind the left atrium. The serous pericardium is thin and covers the heart. It is also called the epicardium. The fibrous pericardium is much thicker. Together they form the pericardial cavity, a thin sac hosting a small amount of fluid.

Fibrous skeleton

The four cardiac valves are kept in their place partly because of the fibrous skeleton of the heart, which is a collection of

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

. It consists of the right fibrous trigone (which along with the membranous

septum In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatri ...

forms the ''central fibrous body''), the left right fibrous trigone, and the conus tendon. The right fibrous trigone is the strongest part of the skeleton. It lies to the right of the

aortic valve The aortic valve is a valve in the heart of humans and most other animals, located between the left ventricle and the aorta. It is one of the four valves of the heart and one of the two semilunar valves, the other being the pulmonary valve. The ...

and connects it with the

mitral The mitral valve (), also known as the bicuspid valve or left atrioventricular valve, is one of the four heart valves. It has two cusps or flaps and lies between the left atrium and the left ventricle of the heart. The heart valves are all one-w ...

and

tricuspid The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, at the superior portion of the right ventricle. The function of the valve is to allow blood to flow from the right atrium to the right vent ...

valves. It is pierced by the

Bundle of His The bundle of His (BH) or His bundle (HB) ( "hiss"Medical Terminology for Health Professions, Spiral bound Version'. Cengage Learning; 2016. . pp. 129–.) is a collection of heart muscle cells specialized for electrical conduction. As part of t ...

. Lastly, the aortomitral curtain is also a part of the fibrous skeleton; it is formed by fibrous tissue connecting two of three of the aortic valve leaflets (the right and non-coronary leaflet) with anterior leaflet of the mitral valve.

The 4 cardiac chambers

The heart has four chambers: the left and right atriums and the left and right ventricles. They form a shallow groove at the line of their junction, which form the atrioventricular groove. The

atrioventricular groove The coronary sulcus (also called coronary groove, auriculoventricular groove, atrioventricular groove, AV groove) is a groove on the surface of the heart at the base of right auricle that separates the atria from the ventricles. The structure co ...

hosts major

coronary arteries The coronary arteries are the arterial blood vessels of coronary circulation, which transport oxygenated blood to the heart muscle. The heart requires a continuous supply of oxygen to function and survive, much like any other tissue or organ of ...

while they travel along to the line of attachment of

atrioventricular valves A heart valve is a one-way valve that allows blood to flow in one direction through the chambers of the heart. Four valves are usually present in a mammalian heart and together they determine the pathway of blood flow through the heart. A heart v ...

. The right and left ventricles are separated by a

, which corresponds to the

interventricular groove Interventricular groove may refer to: * Anterior interventricular sulcus, one of two grooves that separates the ventricles of the heart, near the left margin * Posterior interventricular sulcus, one of the two grooves that separates the ventri ...

s that travel from the posterior to the anterior surface of the heart.

Right atrium

The right atrium lies among the two

, behind and somewhat right of the

sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sh ...

. It is right and anterior to the left atrium. It consists of the venous component (or sina venarum), which is the main, smooth part of the right atrium (auricula or atrium proper). This venous component includes the right appendage, the front and lateral wall of right atrium, and the vestibule of the

tricuspid valve The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, at the superior portion of the right ventricle. The function of the valve is to allow blood to flow from the right atrium to the right vent ...

. The venous component receives the blood from superior and inferior venae cavae. What separates the two components is the inside appearance of the wall. While the sina venarum has smooth walls, the characteristic of the auricula are the thick muscle bundles that make it appear somewhat rough. Sina venarum corresponds to the right horn of sinus venosus of the

embryonic heart Heart development, also known as cardiogenesis, refers to the prenatal development of the heart. This begins with the formation of two endocardial tubes which merge to form the tubular heart, also called the primitive heart tube. The heart is t ...

. Externally, the most prominent features of the heart are the right appendage (or right auricle), the sulcus terminalis, and the

coronary sulcus The coronary sulcus (also called coronary groove, auriculoventricular groove, atrioventricular groove, AV groove) is a groove on the surface of the heart at the base of right auricle that separates the atria from the ventricles. The structure co ...

. The right appendage is pyramidal in shape, with its base opening at the sina venarum. The sulcus terminalis, or terminal groove, is a shallow groove that travels from the IVC to the SVC and separates the right appendage from the venous compartment of the right ventricle. At the upper end of sulcus terminalis lies the

sinoatrial node The sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is an oval shaped region of special cardiac muscle in the upper back wall of the right atrium made up of cells known as pacemaker cells. The sinus node is approximat ...

. The sinoatrial node receives blood supply from a branch of the right coronary artery or circumflex artery in 55% and 45% of people respectively. This artery is called the sinus nodal artery, and it is sometimes visible through the open sternum. Another groove, which runs somewhat parallel and posterior to sulcus terminalis, is Waterstone's groove (also known as Sondergaard's groove). Internally, the

crista terminalis The crista terminalis or terminal crest represents the junction between the sinus venosus and the heart in the developing embryo. In the development of the human heart, the right horn and transverse portion of the sinus venosus ultimately become in ...

is a prominent muscle bundle from which the

pectinate muscles The pectinate muscles (musculi pectinati) are parallel muscular ridges in the walls of the atria of the heart. Structure Behind the crest (crista terminalis) of the right atrium the internal surface is smooth. Pectinate muscles make up the par ...

of the right atrium originate. The terminal crest corresponds to the external sulcus terminalis. The fossa ovalis lies on the interatrial wall and is the remnant of the prenatal atrial communication. The opening of the inferior vena cava is guarded by the

Eustachian valve The valve of the inferior vena cava (eustachian valve) is a venous valve that lies at the junction of the inferior vena cava and right atrium. Development In prenatal development, the eustachian valve helps direct the flow of oxygen-rich blood ...

, while next to it lies the

thebesian valve In the anatomy of the heart, the valve of the coronary sinus (also called the Thebesian valve, after Adam Christian Thebesius) is a semicircular fold of the lining membrane of the right atrium, at the orifice of the coronary sinus. It is situate ...

that guards the

orifice An orifice is any opening, mouth, hole or vent, as in a pipe, a plate, or a body * Body orifice, any opening in the body of a human or animal *Orifice plate, a restriction used to measure flow or to control pressure or flow, sometimes given specia ...

of the

coronary sinus In anatomy, the coronary sinus () is a collection of veins joined together to form a large vessel that collects blood from the heart muscle ( myocardium). It delivers deoxygenated blood to the right atrium, as do the superior and inferior ven ...

. The thebesian veins also drain into the right atrium. Most of the right atrium is

trabecula A trabecula (plural trabeculae, from Latin for "small beam") is a small, often microscopic, tissue element in the form of a small beam, strut or rod that supports or anchors a framework of parts within a body or organ. A trabecula generally has ...

ted, as it is covered with pectinate muscles that run parallel to one another.

Right ventricle

The right ventricle receives blood from the right atrium through the tricuspid valve and pumps it to the lungs. The right ventricle lies behind the sternum and forms a large part of the sternodiaphragmatical surface of the heart. Its inferior surface lies over the central tendon of the diaphragm. The right ventricle consists of an inlet portion that receives blood from the right atrium through the tricuspid valve. There is an apical portion that approaches- but does not reach- the apex of the heart; this apical portion is packed with rough trabeculations. The last portion is a muscular outlet portion (infudibulum) that pumps the blood to the pulmonary artery.The atrioventricular groove, a groove that harbors the right coronary artery of the heart, marks the separation of the atrium and the ventricle. Internally, the crista supraventricularis, a muscular thickener, separates the right ventricle into two spaces.

Left atrium

The left atrium lies to the left and slightly posterior of the right atrium. The pulmonary artery and aorta are located in front of the left atrium. The left atrium is slightly smaller than the right atrium and consists of the venous component, which receives saturated blood from the lungs via four pulmonary veins, the vestibule, and a narrow appendage. The venous component forms a large part of the posterior wall of the heart and the anterior wall of the oblique pericardial sinus.The appendage of the left atrium is a narrow, finger-like entity that contains small pectinate muscles. Its small orifice lies anterior of the left superior pulmonary vein and lateral to the mitral valve. The tip of the appendage can be found in various positions.

Left ventricle

The left ventricle is made of thick muscle walls because a lot of power is needed to push blood to the arterial system of the body. It is conical in shape and occupies part of the anterior (sternocostal), inferior (diaphragmatical), and left wall of heart. It receives blood from the right atrium through the mitral valve and pumps it to the body through the aortic valve. It consists of an inlet portion (ostium venosum), an outlet portion (ostium arteriosum), and an apical portion. The anterolateral and posteromedial papillary muscles are two strong papillary muscles within the left ventricle that anchor the two leaflets of the mitral valve (the valve between left atrium and ventricle consists of two leaflets). While these two muscles have a thick muscular base, they separate into various tendinous cords before entering the leaflets of the mitral valve. The apical portion is conical and consists of fine trabeculations.

Coronary circulation

The heart is supplied blood from two arterial systems: left and right. The major arteries of the two systems travel within the atrioventricular groove and form a crown shape, thus they are named "coronary arteries". There is significant variation of which system provides blood to the inferior surface of the heart. If the PDA starts from the right coronary artery, then the coronary circulation is named as "right dominance", which is the case with 60% of the general population. The arteries are located in the subepicardium, so they are easily visible in the human eye, but in some cases, especially at their initial course, may be sited within the myocardium.

Right coronary system

The right coronary artery usually lies just above the aortic valve, within the aortic root, in the right coronary sinus that is the anterior surface of the aortic root. It travels anteriorly and slightly to the right to reach the atrioventricular groove; it enters the groove and follows it path to reach the cardiac crux, the place where atrioventricular groove meets the interatrial and interventricular grooves at the posterior surface of the heart. The right coronary artery provides blood to the wall of the right heart and some areas of the left heart though its branches. The right coronary system mostly supplies the right ventricle and atrium, apart from the anterior interventricular septum and a small area neighboring the course of the left anterior descending artery.

Left coronary system

The left main coronary artery begins at the posterior sinus of the aortic root. It is the largest coronary artery, as the myocardium supplied by this artery is larger than the coronary artery, although it becomes short as soon as it separates in the anterior interventricular (also known as

left anterior descending The left anterior descending artery (also LAD, anterior interventricular branch of left coronary artery, or anterior descending branch) is a branch of the left coronary artery. Blockage of this artery is often called the ''widow-maker infarction' ...

or LAD) and circumflex artery. The LAD travels within the interventricular groove and gives of diagonal and septal branches. Diagonal branches supply the anterior surface of the heart while septal branches supply the muscle mass of the

interventricular septum The interventricular septum (IVS, or ventricular septum, or during development septum inferius) is the stout wall separating the ventricles, the lower chambers of the heart, from one another. The ventricular septum is directed obliquely backwar ...

; the first one supplies the atrioventricular bundle at the point of its bifurcation. The circumflex artery is embedded within the atrioventricular groove, travels laterally to the left and curves to the posterior surface of the heart, where it usually diminishes at the crux area (where it sometimes supplies the posterior descending artery (in case of left dominance)). The left coronary system mainly supplies the left heart and a large part of the interventricular septum.

Veins and lymphatics

Two separate systems of returning blood from the myocardial mass to the cardiac cavities. The major system consists of the coronary sinus, a wide vessel that collects blood from smaller veins and drains it to the right atrium. The smaller system consists of smaller veins that are draining the inner part of cardiac mass directly to cardiac cavities, most commonly to right atrium. There are three distinct lymphatic drainage plexuses in the heart; after

anastomosing An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be normal ...

each other, they end up in a brachiocephalic node.

Anomalous origin of Coronary arteries

In approximately 1% of humans, coronary arteries originate in a not typical position. Among that 1%, the most common abnormality is Circumflex arising from Right Coronary artery, instead of Left Main Artery and usually does not pose any problem. Other abnormalities are coronary arteries originating from a not typical sinus and then traveling either between the Aorta and pulmonary artery, or intramural. In both cases, outside pressure causes ischaemia and thus angina.

Valves of the heart

There are four major valves in the heart, two

(connecting one atrium to a ventricle) and two arterial (or

semilunar Semilunar can refer to: * Semilunar valves * Semilunar ganglion, or the trigeminal ganglion * An older name for the Lunate bone The lunate bone (semilunar bone) is a carpal bone in the human hand. It is distinguished by its deep concavity and cr ...

) valves guarding the outflow of blood from the human heart. Each atrioventricular valve (tricuspid and mitral valves) consists of the leaflets, the annulus, the tendinous cords, the papillary muscles, and the supporting muscle mass. Semilunar valves (pulmonary and aortic valves) consists of leaflets, the sinuses and the interleaflet triangles.

Aortic valve

Aortic valve is in between the muscular left ventricle and the fibroelastic aorta, the biggest artery of the human body. Its three leaflet close when hydrostatic pressure applies over the valve, while kept open during the ejection phase of the cardiac cycle, when blood is pushed out of the heart by the contracting musculare of the left ventricle. Histologically, the leaflets are fibrous in their core, covered with endothelium; a thickening at their free edge, is named ''node of Arantius''. The aortic leaflets are hinged at the beginning of the aorta, at very first part of aortic sinus. Their line of attachement is not circular, it rather creates a corona, nonetheless it is commonly named as "''aortic ring''". Each of the three aortic valve leaflets is named after the orifice of the coronary artery located above the leaflet- one is named non-coronary leaflet as it lacks a coronary ostium. Left and right leaflet originate from the muscle fibers of left ventricle, while non coronary leaflet is in continuation with mitral valve's anterior leaflet forming the ''aortic-mitral curtain''.

Mitral valve

Mitral valve separates left atrium with left ventricle. It consists of the two mitral leaflets, (anterior and posterior) sited within the mitral annulus.

Chordae tendineae The chordae tendineae (tendinous cords), colloquially known as the heart strings, are inelastic cords of fibrous connective tissue that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart. Structure The chordae ...

are attached to the ventricular surfaces and the free edges of the two leaflets. Chordae are also attached to the two papillary muscles of left ventricle.

Tricuspid valve

Tricuspid valve separates right champers- atrium from ventricle. As its name suggest, it has 3 leaflets (anterior, posterior and septal), all attached at the annulus of the leaflet that notably lacks any fibrotic tissue. Apart from the leaflets and annulus, it also consists of three papillary muscles and three sets of chordae tendineae.

References

Sources

* * * * * * * * * *{{cite book, last=Zhu, first=Xiaodong , title=Surgical Atlas of Cardiac Anatomy, url=https://books.google.com/books?id=wYShBQAAQBAJ, year = 2015, publisher=Springer, isbn=978-94-017-9409-1 Heart Cardiac anatomy Organs (anatomy)