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The Heart - Anatomy
[mere rearrangement of Dr. Amjad Shatarat’s slides]
General Information
The heart is a double, self-adjusting suction and pressure pump, slightly larger than one’s loosely clenched fist. It’s a pair of valved muscular pumps combined in a single organ in the shape of a pyramid that’s fallen over and resting on one of its sides. The Heart is composed of a base, an apex and 4 surfaces: left and right pulmonary, inferior [diaphragmatic] and anterior [sternocostal] surfaces. THE HEART’S STRUCTURE
Part Formed by: Location Notes
The apex The inferolateral part of the left
ventricle Directed downward, forward and to the left, posterior to the left 5th intercostal space, 9cm from the median plane It’s where the sound of the mitral valve closure are maximal, the apex underlies the site where the heartbeat may be auscultated
The base Mainly by the left atrium and a
little contribution from the right atrium Posteriorly facing T6-T vertebrae separated from the vertebrae by the pericardium, oblique pericardial sinus, oesophagus and aorta
The sternocostal [anterior]
surface
Mainly by the right atrium and right ventricle
The diaphragmatic [inferior]
surface
Mainly by the right and left ventricles [separated by the interventricular groove] And the inferior surface of the right atrium [where the IVC opens] Related mainly to the central tendon of the diaphrgm
The left pulmonary surface The left ventricle and a portion of
the left atrium faces the left lung Board and conex Forms the cardiac impression in the left lung
The right pulmonary surface The right atrium^ Broad and convex
ON THE HEART’S SURFACE
Structure Location Contents
The coronary sulcus circles the heart, separating the atria from the
ventricles
- The right coronay artery
- The small cardiac vein
- The coronary sinus
- The circumflex branch of the left coronary artery
The anterior interventricular sinus on the anterior surface of the heart^ 1. The anterior interventricular artery
- The great cardiac vein
The posterior interventricular sinus on the diaphragmatic surface of the heart^ 1. The posterior interventricular artery
- The middle cardiac vein ● The wall of the heart is composed of cardiac muscle:
- Myocardium -> covered externally by serous pericardium
- Epicardium -> lined internally with endothelium
- Endocardium ● The fibrous skeleton of the heart is a complex framework of dense collagen forming:
- Four fibrous rings [L. annuli fibrosi] surround the orifices of the valves
- The right and left fibrous trigone formed by the connection between the rings
- The membranous parts of interatrial and interventricular septa. ● Importance of the fibrous skeleton:
- Keeps the orifices patent and prevents them from being overly distended by the increased volume pressure from pumping blood
- Provides attachment for the leaflets and cusps of the valves
- Provides attachment for the myocardium
- Form an electrical insulator by separating the atria and the ventricles and the conducted impulses ensuring that they contract independently and by surrounding and providing passage for the initial part of the AV bundle of the conducting system of the heart.
CHAMBERS OF THE HEART : Right and left atria [sing. atrium], and right and left ventricles.
Chamber Cavities Structure/Parts Openings Notes
The right atrium A main cavity and a
small outpouching auricle*
- The right auricle is a triangular-shaped superior portion of the rt. atrium that is like an add-on room that increases the- capacity of the rt. atrium as it overlaps with the ascending aorta. It’s not usually well-demarcated from the rest of the atrium. It’s a point of entry for the cardiac surgeon.
- Posterior smooth-walled -> derived from the embryonic sinus venosus in which enter the SVC and IVC
- Thin-walled anterior trabeculated part the constitutes the original embryonic right atrium
- Pectinate muscles on the lateral aspect of crista terminalis, run laterally and generally parallel to each other along the free wall of the atrium
- The superior vena cava -> returns blood from the head, neck and upper limbs and receives blood from the chest wall via the azygos system. Opens into the upper part of the atrium.
- The inferior vena cava -> drains blood from all the structures below, and including, the diaphragm. Opens into the lower part of the atrium, anterior to its orifice is a flap-like valve: Eustachian valve [valve of IVC]
- The coronary sinus -> drains most of the blood from the heart wall and opens into the venous atrial component between the orifice of IVC, the fossa ovale and the vestibule of atrioventricular opening. Guarded by a semicircular valve that covers the lower part of the orifice called Thebesius’ or Thebesian valve.
- Several small venous ostia draining the minimal atrial veins are scattered on the atrial [mainly septal aspect ] wall. The anterior cardiac veins and the right marginal vein may enter the atrium through larger ostia. The two parts of the rt. atrium are separated by the ridges of the Crista Terminalis muscle: most prominent superiorly next to the SVC orifice then fades out to the right of the IVC ostium in position that corresponds with the sulcus terminalis externally. The Eustachian valve is large during fetal life as it serves to direct oxygenated blood from the placenta through the foramen ovale of the atrial septum into the left atrium. The fossa ovalis is fetal remnants in the right atrium that is a shallow depression which was the site of foramen ovale in the fetus. The annulus ovalis forms the upper margin of the fissa. Both located on the atrial septum. *Auricle: is a term used improperly instead of the atrium. It’s called atrial appendage not auricular appendage. The term auricular fibrillation is clinically incorrect, it should be atrial fibrillation
The right ventricle 1. Inflow portion that
contains the tricuspid valve and structure called “Trabeculae Carneae”
- prominent ridges attached to the ventricular wall
- when attached on both ends they form bridges
- papillary muscle: a. anterior papillary muscle -> largest and most constant and arises from the ant. wall b. posterior papillary muscle -> may consist of one, two or three structures with some chordae tendineae arising directly from the ventricular wall c. septal papillary muscle -> most inconsistent [small or absent] with chordae tendineae arising from the septal wall *The septomarginal [moderator] band forms a bridge between the ant. papillary muscle and lower part of the interventricular septum.
- The smooth-walled outflow tract that leads to the pulmonary trunk and is called “Conus arteriosus”
- The right atrioventricular orifice -> communication with the rt. atrium, guarded by the Tricuspid valve that consists of three cusps formed by a fold of endocardium with some C.T. 2.The pulmonary orifice -> communication with the pulmonary trunk *The septomarginal [moderato] band carries a portion of the cardiac conduction system, the right bundle branch to the anterior wall of the right ventricle. Facilitates conduction time allowing coordinated contraction of the ant. papillary muscle. *The atrium contracts when the ventricle relaxes. Blood enters [inflow] to the posterior part and when the ventricle contracts it’s pushed to the outflow portion into the pulmonary tract superiorly and to the left. With the help of the supraventricular crest , which deflects the incoming flow into the main cavity of the ventricle and the outgoing flow into the conus arteriosus towards the pulmonary orifice, the blood flow takes a U-shaped path, changing direction about 140 degrees.
● The interventricular / ventricular septum -> is a strong, obliquely placed partition between the right and left ventricles and forms
part of the walls of each. It’s formed by muscular and membranous parts.
- The muscular part has the thickness of the remainder of the wall of the left ventricles [which is thicker than the right ventricle’s wall because of the much higher pressure in the left one]. The IVS bulges into the cavity of the rt. ventricle.
- The membranous part is formed superiorly and posteriorly by a thin membrane from the fibrous skeleton of the heart. The septal cusp of the tricuspid valve is attached to the middle of this membranous wall. Inferiorly to this we have the interventricular septum and superiorly we have the atrioventricular septum separating the right atrium and left ventricle. THE VALVES OF THE HEART: function to maintain unidirectional flow of blood
- Atrioventricular -> right/tricuspid and left/mitral/bicuspid
- Semilunar -> aortic and pulmonary
The atrioventricular valvular complex consists of:
- The orifice and its associated annulus [riing]
- The cusps, the supporting chordae tendineae and the papillary muscles
Histology of heart valves: The cusps are composed of connective tissue with over-lying endocardium. Avascular structures. [3 layers]
- Spongia -> loose connective tissue located on the atrial or blood vessel [aorta or pulmonary] side of each valve.
- Fibrosa -> forms the core of the valve and contains fibrous extensions from the dense irregular c.t of the skeletal rings or the heart
- Ventricularis -> immediately adjacent to the ventricular surface of each valve and is covered with endothelium. It contains dense c.t with many layers of elastic fibers and, in AV valves, it’s continuous with chordae tendinae. ● Valves are avascular -> small blood vessels and smooth muscle are only found near the base of the cusp. They are exposed to blood on both surfaces and thin enough to allow exchange of nutrients by diffusion. ● Valvulitis -> inflammation of the heart valves caused by rheumatic fever. This inflammation induces angiogenesis and vascularisation of the valves [mainly the mitral valve (65-70%) and then the aortic (20-25%)]. It can lead to progressive replacement of the valve’s elastic tissue [in ventricularis] by irregular masses of collagen fibers causing the valve to thicken. They become rigid and inflexible which affects their ability to open and close.
Structure of atrioventricular valves:
- The extreme edges of the cusps are thin and delicate with a sawtooth appearance from the insertion of chordae tendineae.
- Away from the edge, the atrial surface contains nodules [mainly present in children] called The noduli Albin.
- The noduli albini -> minute fibrous nodules on the margins of the mitral and tricuspid valves.
The papillary muscles and chordae tendineae.
● The bases of the cusps are attached to the fibrous ring of the skeleton of the heart whereas their free edges and ventricular surfaces are attached to the chordae tendineae. ● The papillary muscles -> contract when the ventricles contract and prevent the cusps from being forced into the atrium and turning inside out as the intraventricular pressure rises. ● Chordae tendineae -> are fibrous collagenous structures supporting the cusps of AV valves. The tendinous cords that arise from the apices of the papillary muscles attach to the free edges and ventricular surfaces of the cusps [connects the cusps to the papillary muscles].
- During the contraction -> the chordae tendineae of the papillary muscles are connected to the adjacent parts of two cusps. On the closure of an AV valve, the narrow border between the row of Albini nodules and the free edge of each cusp presses against that of the next resulting in a secure, watertight closure.
- The papillary muscle begins to contract before contraction of the ventricles, tightening the tendinous cords and drawing the cusps together. The chords prevent separation of the cusps because they’re attached to adjacent sides of two cusps and prevent prolapsing as ventricular pressure rises. Thus, blocking regurgitation of blood during ventricular systole. The papillary muscle insures competence of the valve.
Atrioventricular valves
Valve Location Structure Notes
Tricuspid [right AV] valve guards the right atrioventricular orifice between the right atrium and right ventricle Consists of three cusps [anterior, septal and inferior] or leaflets, the bases are attached to a fibrous ring around the orifice [annulus fibrosus] -> to keep the caliber of the orifice constant. Measures on average 11.4 cm. The atrial surface is smooth, the ventricular surface is irregular because of the insertion of chordae tendineae. The orifice best seen from atrial aspect It’s almost vertical [45 degrees on the sagittal plane]
Mitral [Bicuspid or left AV] valve guards the left atrioventricular orifice between the left atrium and left ventricle Consists of two cusps The subaortic curtain [mentioned above] The left AV orifice admits atrial blood during diastole and the flow is towards the apex. After closure of the mitral cusps, and throughout the ejection phase of systole, blood is expelled from the apex through the aortic orifice. And takes a 180 degrees turn around the anterior cusp of the mitral valve [mentioned above somewhere as well]. The orifices and cusps of both AV valves undergo considerable change in position, form and area during a cardiac cycle. Both valves move anteriorly and to the left during systole and reverse their motion during diastole. The mitral valve reduces its orificial [anular] area by as
much as 40% during systole.
Semilunar valves
● No chordae tendineae or papillary muscles. ● No distinct circular ring of fibrous tissue at the base of the arteries from which these valves arise ● The arterial wall expands into three dilated pouches, the sinuses of valsalva. ● Consist of three pocket-like cusps of approximately equal size.
Structure of semilunar valve:
- Largely smooth and thin
- At the centre of the free margin of each cusp is a small fibrous nodule called The nodulus Arantii.
- On each side of the nodule along the entire free edge of the cusp, there’s a thin, halfmoon-shaped area called Lunula that has fine striations parallel to the edge.
- The cusps are named according to their position in the fetus before the heart rotates to the left.
- The official nomenclature refers to an anterior, a posterior and a septal cusps according to their position in the fetus. The position changes with development and in adults we have anterior, right and left semilunar cusps. ● The edge of each cusp is thickened in the region of contact forming Lunule, the apex of each angulated free edge is thickened further.
Valve Location Structure Notes
Aortic valve opening of the aorta^ Consists of three cusps
[posterior, left and right] Superior to the right and left cusps in the Sinus of Valsalva are the openings of the right and left coronary arteries
Pulmonary valve At the apex of the infundibulum,
the outflow tract of the right ventricle, the opening into the pulmonary trunk Consists of three cusps [anterior, left and right] with free edges projecting upwards into the lumen of the pulmonary trunk. During the diastole, the valve is closed and all three cusps are tightly apposed, then it opens passively during systole and then closes rapidly at the end of systole..
HEART BLOOD SUPPLY
The endocardium and subendocardial tissue receive nutrients and oxygen directly by diffusion or microvasculature from the heart chambers. The rest of the heart: from the coronary arteries [right and left].
- Two arteries form an oblique inverted crown, in which an anastomotic circle in the atrioventricular groove is connected by marginal and interventricular loops intersecting at the cardiac apex
- The arteries originate from the ascending aorta in the Sinus of Valsalva, superior to the right and left semilunar cusps. [no arteries arise from the posterior cusp]
Artery Origin Course Branches Supply to Notes
Left coronary artery
[LCA]
Left sinus valsalva, superior to the left cusp from the ascending aorta Between the left auricle and the left side of the pulmonary trunk
- Anterior interventricular [left anterior descending LAD]
- Circumflex artery *Left diagonal artery may arise directly from LCA trunk
- Most of the left ventricle
- A small area of the right ventricle to the right interventricular groove
- The anterior ⅔ of the ventricular septum Has short [0.5-2cm] common stem
Supply to the conduction system :
Part Supply Notes
SA node 1.Mainly by the RCA [ sinoatrial nodal artery
in 60%]
- Sometimes by the LCA [circumflex branch in 40%] There’s a common variation in the origin of the sinoatrial nodal artery
AV node and AV bundle The right coronary artery
Right bundle branch RBB the LCA
Left bundle branch LBB the RCA and LCA
VENOUS DRAINAGE OF THE HEART
- Coronary sinus -> lies in posterior coronary sulcus [post. atrioventricular groove] drains most blood of the heart into the right atrium.
- Tributaries of the coronary sinus: a. Great cardiac vein -> the main tributary, lies in the anterior interventricular sulcus with LAD b. Middle cardiac vein -> lies in the posterior interventricular sulcus with the posterior interventricular artery c. Small cardiac vein
- Venae cordis minimae [thebesian veins] and anterior cardiac veins -> open directly to the chambers of the heart.
