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| | {{Anatomy of the heart}} |
| {{CMG}}; '''Assistant Editor(s)-in-Chief:''' [[User:Rim Halaby|Rim Halaby]], [[User:YazanDaaboul|Yazan Daaboul]] | | {{CMG}}; '''Assistant Editor(s)-in-Chief:''' [[User:Rim Halaby|Rim Halaby]], [[User:YazanDaaboul|Yazan Daaboul]] |
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| ==Overview==
| | {{SK}} Heart anatomy |
| The [[mediastinum]] occupies the center of the thoracic cavity between the pulmonary viscera. It spans superiorly at the level of the thoracic aperture, inferiorly at the diaphragm, and from the sternum to the costal cartilages and bodies of vertebrae T1 to T12 antero-posteriosly. With the exception of the lungs, the mediastinum involves all thoracic viscera. For the purpose of description, the mediastinum is divided into superior, middle and inferior sections. The heart, its roots of the great vessels (ascending aorta, pulmonary trunk, superior vena cava), and the pericardium occupy the middle mediastinum.
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| ==The Pericardium== | | ==[[Anatomy of the heart overview|Overview]]== |
| *The pericardium is a sac that embeds the heart. It is pierced by the great vessels. Morphologically, it is a conical-shaped, double-walled fibro-serous membrane.
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| *The pericardial sac rests posteriorly to the sternum at the level of second to sixth costal cartilages and T5-T8 vertebrae.
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| *The pericardium is made of two layers:
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| **Fibrous pericardium
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| ***Hard protective external layer
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| ***Attached to sternum anteriorly by sterno-pericardial ligaments and fused with the central tendon of the diaphragm and great vessels to allow mobility of the pericardial sac against sudden cardiac overfilling.
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| **Serous Pericardium
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| ***Smooth internal layer made of 2 components:
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| ****Parietal: reflects onto fibrous pericardium
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| ****Visceral: reflects onto heart and great vessels and forms the epicardium, the external layer of the heart wall.
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| *Pericardial cavity: Potential space between parietal and visceral layers. It contains a serous fluid film that occupies the cavity and functions as lubricant against friction by all chest movements.
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| ===Pericardial Sinuses=== | | ==[[Anatomy of the heart the pericardium|The Pericardium]]== |
| *Pericardial sinuses are channels or chambers between the visceral and parietal pericardia.
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| *Transverse sinus:
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| ** Located posterior to the pulmonary trunk and ascending aorta at the level between the superior vena cava and aortic arch.
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| ** Formed after dorsal mesocardium rupture embryonically
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| **Functional role is to allow the unhindered expansion of great arteries posteriorly during cardiac systole.
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| **Utilized surgically to pass surgical clamps or place ligatures around great arteries.
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| *Oblique sinus:
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| **A blind recess (cul-de-sac) posterior to the left atrium between superior vena cava, right and left pulmonary veins inferior to the transverse sinus.
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| ** Formed embryonically by the incorporation of the pulmonary vein tributaries into the left atrium.
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| ** Functional role believed to be the expansion of the left atrium upon normal collapse of the thorax.<ref = “Kishore”>Kishore, K. (2003). The Heart of Structural Development: The Functional Basis of the Location and Morphology of the Human Vascular Pump. J Postgrad Med, 49:282-4.</ref><ref = "Moore">Moore, K. L., Agur, A. M., & Dalley, A. F. (2011). Essential Clinical Anatomy - Fourth Edition. Lippincott Williams & Wilkins.</ref><ref = "Tank">Tank, P. W. (2009). Grant's Dissector - Fourteenth Edition. Lippincott Williams & Wilkins.</ref>
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| ;Below are images showing the pericardium and pericardial sinuses.
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| <gallery heights="125" widths="125">
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| Image:Pericardium.JPG|The pericardium
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| Image:Pericardial sinuses.JPG|The pericardial sinuses
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| </gallery>
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| ==External and Internal Features of the Heart== | | ==[[Anatomy of the heart external and internal features of the heart|External and Internal Features of the Heart]]== |
| ===Layers of the Heart===
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| *The heart wall consists of 3 layers:
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| **'''Epicardium''': thin external layer formed by visceral layer of serous pericardium
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| **'''Myocardium''': thick middle layer made of cardiac muscle
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| **'''Endocardium''': thin internal membrane that lines the heart and its valves. It is composed of endothelium and sub-endothelial connective tissue, similar to intimal component of blood vessels.
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| ===External Features=== | | ==[[Anatomy of the heart right atrium|Right Atrium]]== |
| *The [[heart]] and roots of great vessels are embedded in the pericardial sac, approximately in the center of the thorax. The size of the heart is slightly larger than a clenched fist. The heart is surrounded laterally and posteriorly by the lungs, and anteriorly bound by the sternum and medial sections of the ribs and sterno-costal joints.
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| *It has the shape of a three-sided pyramid with an apex (left anterior), a base (posterior), and 4 surfaces: Sterno-costal/anterior (formed by right ventricle), diaphragmatic/inferior (formed by left ventricle and part of right ventricle), left pulmonary (formed by left ventricle, in contact with left lung), and right pulmonary (formed by right atrium).
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| *The heart appears trapezoid in the posterior and anterior views. As such, it consists of 4 borders: Right (convex), Inferior (horizontal), left (oblique), and superior.
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| ;Below is an image showing a schematic outline of the heart in the mediastinum.
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| [[Image:Outline_Heart.svg.png|350px|A schematic outline of the heart. Note that the valves are named in the figured as follows: A for aortic valve, P for pulmonary valve, B for bicuspid valve and T for tricuspid valve]]
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| *The external surface of the heart is notable for 3 main sulci (grooves):
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| **'''Coronary (atrioventricular) sulcus''': runs around the heart, and separates atria from ventricles
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| **'''Anterior interventricular sulcus''': runs along the interventricular septum anteriorly
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| **'''Posterior interventricular sulcus''': runs along the interventricular septum posteriorly
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| ===Internal Features===
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| *The heart has 4 chambers: Right and left atria and right and left ventricles.
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| *Blood flows normally in the right to left direction: Right atrium to right ventricle to left atrium, and finally to left ventricle.
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| *Oxygen-depleted blood reaches the right atrium via the coronary sinus and superior and inferior vena cava and evacuates the right ventricle via the pulmonary artery towards the lungs.
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| *Oxygen enriched blood then re-enters the left atrium via 4 pulmonary veins and evacuates the left ventricle via the aorta.
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| ;Below is an image showing the atria and ventricles of the heart as well as arrows indicating the normal blood flow throught the heart valves.
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| <gallery heights="225" widths="275">
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| Image:Diagram of the human heart (cropped).svg|Anterior (frontal) view of the opened heart. White arrows indicate normal blood flow.
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| </gallery>
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| </div>
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| ==Right Atrium== | | ==[[Anatomy of the heart left atrium|Left Atrium]]== |
| *The right [[atrium]] forms the right border of the [[heart]].
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| *The [[superior vena cava]] and the [[inferior vena cava]] drain systemic venous blood into the smooth posterior wall of the right [[atrium]].
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| *In contrast, the right [[atrium]]’s anterior wall is ridge-like; it is composed internally of pectinate muscles, a rough muscular wall.
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| ====Right auricle:====
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| *The right [[atrium]] contains a right auricle, an ear-like conical muscular pouch that overlaps the ascending aorta.
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| *The right auricle is an embryonic structural remnant that allows the right atrium to increase its capacity.
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| ====Opening of the superior and inferior vena cava:====
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| *The [[superior vena cava]] opens in the interior right atrium at its superior part, at the level of the right third costal cartilage.
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| *The [[inferior vena cava]] opens in the interior right atrium at its inferior part, almost in line with the superior vena cava at approximately the level of the fifth costal cartilage.
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| ====Coronary Sinus:====
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| *It is a venous collection, whereby systemic blood is received at the posterior part of the coronary groove from the [[cardiac veins]] into the coronary sinus. The latter is a derivative of an embryonic structure called the venous sinus.
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| *The opening or orifice of the [[coronary sinus]] is located between the right atrioventricular orifice and the inferior vena cava orifice.
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| ====Sinus Venarum:====
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| *The adult right [[atrium]] also contains posteriorly a smooth-walled pouch called sinus venarum, on which the coronary sinus, and superior and inferior vena cava bring poorly oxygenated blood to the heart.
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| *Sinus venarum is formed by the incorporation of the venous sinus (L. sinus venosum), an embryonic structure, into the primordial atrium. As a result, sinus venarum provides further capacity for the right atrium.
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| *The sinus venorum is separated from the primordial atrium by means of 2 structures: the sulcus terminalis (terminal groove) externally which extends from the front of the superior vena cava to the front of the inferior vena cava, and represents the line of union of the sinus venosus of the embryo with the primitive atrium. Internally, the separation is indicated by the crista terminalis (terminal crest).
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| ====Fossa Ovalis:====
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| *Fossa ovalis is a depression in the inter-atrial septum.
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| *It is a remnant of the foramen ovale, an embryonic physiological shunt, significant for fetal oxygenation and nutrition from the mother’s [[placenta]] to fetus’s left [[atrium]] without passing through the [[lungs]].
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| *The limbus of the fossa ovalis (annulus ovalis) is the prominent oval margin of the fossa ovalis.
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| *It is located on the medial wall of the right [[atrium]] and circumscribes the septum primum the fossa ovalis anteriorly, posteriorly, and superiorly.
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| ==Left Atrium== | | ==[[Anatomy of the heart right ventricle|Right Ventricle]]== |
| *The left [[atrium]] is the major component of the [[heart]] base.
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| *The interatrial septum is part of the left atrial wall; it runs posteriorly and to the right. Its wall is slightly thicker than that of the right [[atrium]].
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| *The interior of the left [[atrium]] is characterized by two main pouches:
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| **A larger smooth-walled part, believed to be formed by absorption of parts of embryonic pulmonary veins.
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| **A smaller muscular auricle with pectinate muscles, believed to be remnant of left part of primordial atrium.
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| ====Pulmonary Veins:====
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| *Blood enters the left [[atrium]] on the posterior wall via 4 valveless pulmonary veins, arranged in two pairs, left and right.
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| ====Left Auricle:====
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| *Similar to the right [[atrium]], the left atrium also contains a left auricle.
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| *In contrast to the right auricle which overlaps the ascending aorta, the left auricle forms the superior part of the left border of the heart and overlaps the pulmonary trunk.
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| *The left auricle is a small muscular region containing pectinate muscles inside.
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| ====Left Atrio-Ventricular Orifice:====
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| *At the level of the left atrio-ventricular orifice, the outflow of oxygenated blood received from the pulmonary veins evacuates the left atrium.
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| ==Right Ventricle== | | ==[[Anatomy of the heart left ventricle|Left Ventricle]]== |
| *The right [[ventricle]] forms almost the entire inferior border of the [[heart]], the largest part of the anterior surface of the [[heart]], and also contributes to the diaphragmatic surface.
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| *The interior of the right [[ventricle]] has irregular muscle elevations called '''trabeculae carneae'''.
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| *The flow of blood in the right ventricle:
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| **The inflow of blood into the right ventricle enters first posteriorly.
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| **The outflow of blood leaves superiorly and to the left at the level of the pulmonary trunk.
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| **Therefore, blood takes a U-shaped path through the right ventricle in a total tract length of 2 cm.
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| ====Tricuspid Valve==== | |
| *The inflow part receives deoxygenated blood from the right [[atrium]] through the right atrioventricular or tricuspid, orifice via the [[tricuspid valve]].
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| *The orifice is a located retro-sternally between fourth and fifth intercostal spaces.
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| *It is characterized by a unique fibrous ring that resists dilation due to pressure variations.
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| *The tricuspid valve contains 3 cusps: anterior, posterior, and septal.
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| *The valve cusps play an important role in preventing blood regurgitation from the right ventricle to the right atrium during ventricular contraction.
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| *Hence when blood is forced through the right atrio-ventricular orifice, the [[tricuspid valve]] cusps are pushed aside.
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| ;Below is an image Courtesy of Professor Peter Anderson DVM PhD and Published with permission. [http://www.peir.net © PEIR, University of Alabama at Birmingham, Department of Pathology]
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| <div align="left">
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| <gallery heights="117" widths="117">
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| Image:415.jpg|Mitral and tricuspid valves from atria. Normal valvular anatomy
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| </gallery>
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| </div>
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| ====Tendinous Chords====
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| *All [[tricuspid valv]]e cusps are attached on their free edges and ventricular surfaces via delicate tendons called tendinous chords (L. chordae tendineae) on their free edges; with each chord attaching simultaneously 2 adjacent valve cusps.
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| *The tendinous chords function in preventing valvular prolapse when ventricular pressure rises due to ventricular contraction.
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| ====Papillary Muscles====
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| *Papillary muscles are three projections whose apices give rise to tendinous chords.
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| *Their bases are attached to the wall of the right ventricle.
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| *With respect to the right ventricle, they are located anteriorly, posteriorly, and septally and hence named accordingly.
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| **The anterior [[papillary muscle]] is the largest, while the septal is the smallest and mayb be multiple.
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| *Significantly, papillary muscles contract before contraction of the right ventricular in order to tighten the tendinous chords. As such, the tricuspid valve closes by drawing the cusps together before ventricular contraction and blood is prevented from regurgitation to the right atrium.
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| ====Interventricular Septum====
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| *Interventricular septum is a strong oblique wall between the right and left ventricles. It is composed of two parts:
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| **'''Membranous''': thin, superoposterior part and continuous with the fibrous skeleton of the heart.
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| **'''Muscular''': thick bulge into the cavity of the right ventricle. The prominent bulging is due to the overwhelming pressure in the left ventricle with respect to its counterpart in the right side.
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| ====Septomarginal Trabecula (Moderator Band)====
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| *The septomarginal trabecula is a curved muscular bundle running from the inferior part of the inter-ventricular septum to the base of the anterior papillary muscle.
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| *It carries part of the right bundle branches of the AV bundle, necessary for electrical conduction, to the anterior papillary muscle of the right [[ventricle]].
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| *It is believed that via this conduction route that the anterior papillary muscle achieves its coordinated contraction.
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| ====Pulmonary Valve====
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| *The pulmonary valve is located at the apex of the conus arteriosus (infundibulum), a smooth-walled, cone-shaped portion of the right ventricle inferior to the opening of the pulmonary trunk (pulmonary artery).
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| *It is at the level of the left third costal cartilage.
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| *The pulmonary valve contains three semilunar cusps: anterior, right, and left.
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| *Each [[semilunar valve]] is concave when viewed superiorly and has three structures: one fibrous nodule and two lunules.
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| *The nodule and the lunules help sealing the valve cusps a prevent backflow of blood during diastole.
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| ====Pulmonary Sinus and Pulmonary Trunk====
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| *Pulmonary sinuses are the spaces at the origin of the pulmonary trunk between the dilated wall of the vessel and each cusp of the pulmonary valve.
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| *Blood in the pulmonary sinuses prevents sticking of the cusps to the walls of the pulmonary trunk and consequential failure to close.
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| ==Left Ventricle==
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| *The left [[ventricle]] is characterized by its thick muscular wall that covered by more numerous trabeculae carneae than in the right ventricle.
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| *Muscularization of the left ventricle grants it a sufficient work performance to pump blood appropriately to the systemic circulation and to feed all vascular beds.
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| ====Mitral (Bicuspid) Valve====
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| *The left ventricle contains the [[mitral valve]] at the level of the AV orifice. The mitral valve is located substernally at the fourth sternocostal junction.
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| *It is composed of 2 cusps: anterior and posterior.
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| * The mitral valve is attached to the left [[ventricle]] by two papillary muscles: anterior and posterior, each giving rise to tendinous cords to both cusps simultaneously.
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| *Although functionally similar to the papillary muscles in the right ventricle, the anterior and posterior papillary muscles in the left ventricle are anatomically larger.
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| ====Aortic Vestibule====
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| *The aortic vestibule is a supero-anterior component of the left ventricle that delineates the left ventricle’s outflow tract.
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| *In contrast to the muscular component of the left ventricle, the aortic vestibule is fibrous smooth-walled structure that is non-muscular.
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| *At the end of the aortic vestibule in its right postero-superior part lies an oblique [[aortic valve]] and the aortic orifice, the beginning of the ascending aorta.
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| ====Aortic (Semilunar) Valve====
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| *The left [[ventricle]] and the aortic orifice are separated by the aortic valve.
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| *It is located substernally near the left sterno-costal junction.
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| *Similar to other valves in the heart, the [[aortic valve]] is surrounded by a fibrous ring that allows the three valve cusps to attach to.
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| *The three [[aortic valve]] semilunar cusps are named according to their position: right, posterior, and left.
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| ====Aortic Sinuses====
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| *Aortic sinuses are bulges at the base of the ascending aorta between its wall and the aortic valve cusps that give rise to the coronary arteries, the arteries that supply the myocardium with oxygen and nutritional demands.
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| *The right aortic sinus is associated to the right coronary artery; the left aortic sinus is associated to the left coronary artery, while the posterior aortic sinus is not associated with any [[coronary artery]]. Thus it is called the non-coronary sinus.
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| ==Sources== | | ==Sources== |
| *Kishore, K. (2003). The Heart of Structural Development: The Functional Basis of the Location and Morphology of the Human Vascular Pump. J Postgrad Med, 49:282-4. | | *Kishore, K. (2003). The Heart of Structural Development: The Functional Basis of the Location and Morphology of the Human Vascular Pump. J Postgrad Med, 49:282-4. |
| *Moore, K. L., Agur, A. M., & Dalley, A. F. (2011). Essential Clinical Anatomy - Fourth Edition. Lippincott Williams & Wilkins. | | *Moore, K. L., Agur, A. M., & Dalley, A. F. (2011). Essential Clinical Anatomy - Fourth Edition. Lippincott Williams & Wilkins. |
| *Tank, P. W. (2009). Grant's Dissector - Fourteenth Edition. Lippincott Williams & Wilkins. | | *Tank, P. W. (2009). Grant's Dissector - Fourteenth Edition. Lippincott Williams & Wilkins. |
| ==References==
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