Anatomy of Heart
Location of heart:
Heart lies in the middle mediastinum. 1/3rd of the heart lies to the right and 2/3rd to the left of the midline. It lies opposite to T5 – T8 vertebrae in supine position & T6 – T9 vertebrae in erect position.
Dimensions of heart:
Base to apex-12cm; Transversely- 8-9cm; Anteroposteriorly- 6cm.
Weight: In males it weighs: 280-340 gm and in females : 230-280 gm
Describe the external features of Heart.
External features of heart
The heart has:
An apex: It is formed by the left ventricle. It lies in the fifth intercostal space 9 cms. from the median plane.
Three surfaces
Sternocostal surface: Is formed by right atrium, right ventricle, left auricle & left ventricle.
Left surface: Is formed by left auricle and left ventricle.
Diaphragmatic surface: 2/3rd is formed by left ventricle and 1/3rd by right ventricle.
Posterior surface/Base: It is quadrilateral in shape.
2/3rd of base is formed by posterior surface of left atrium and 1/3rd by right atrium.
It lies opposite to T5-T8 vertebra in supine position.
Four borders
Superior border: is formed by the two atria.
Right border: Right atrium
Inferior border : Mainly by right ventricle and near the apex by left ventricle.
Left border : Is formed by left auricle and left ventricle.
Five sulci
Atrioventricular sulcus (coronary sulcus): it is a groove on the heart's surface that separates atria from ventricles.
It contains
Right Coronary Artery (RCA)
Left Circumflex Artery (LCx).
Coronary Sinus: This large vein is located in the posterior part of the coronary sulcus. It collects deoxygenated blood from the heart muscle and drains into the right atrium.
Small Cardiac Vein: This vein travels alongside the right coronary artery in the coronary sulcus and also drains into the coronary sinus.
Great Cardiac Vein: This vein runs alongside the left coronary artery in the anterior part of the coronary sulcus and continues into the coronary sinus.
right coronary artery, circumflex branch of the left coronary artery, & small cardiac vein.separates atria from ventricles .
Anterior interventricular sulcus: separates right and left ventricles on the sternocostal surface.
Posterior interventricular sulcus: separates right and left ventricles on the diaphragmatic surface.
Interatrial sulcus: Separates right atrium from the left atrium .
Sulcus terminalis: extends from the opening of superior vena cava to inferior vena cava and separates the rough part from the smooth part of the right atrium.
What are the posterior relations of base of Heart?
Following are the posterior relations of the Base of heart:
Oblique sinus of pericardial cavity
Right pulmonary veins
Descending thoracic aorta
Middle four thoracic vertebrae
Applied Aspects
Apex beat
Is the lowermost and outermost thrust of the heart, felt on the front of the chest. In adults it is felt in the left 5th intercostal space 9cm. from the median plane (just medial to the midclavicular line). In infants it is felt in the 3rd intercostal space just lateral to the midclavicular line.
Dextrocardia
It is a congenital anomaly in which the heart lies on the right side of the thoracic cavity. This may be associated with the reversal of all the abdominal organs, a clinical condition known as situs inversus.
What are the chambers of Heart?
Heart consists of four chambers
Right atrium : Receives the impure blood from the body and the heart itself.
Right ventricle: Receives the impure blood from the right atrium and outflows the blood into the pulmonary circulation through the pulmonary trunk.
Left atrium : Receives oxygenated blood from the lungs via pulmonary veins.
Left ventricle : Receives oxygenated blood from the left atrium and outflow the blood into the systemic circulation via aorta.
Describe the internal features of right atrium.
The interior of the right atrium is divided into 2 parts:
Smooth posterior part – It is also called sinus venarum. All the veins except anterior cardiac veins open into this part (e.g., SVC, IVC, coronary sinus, and venae cordis minimae)
Rough anterior part – It presents number of muscular ridges, the musculi pectinati which arise from the crista terminalis and run forwards towards the auricle.
The two parts are separated from each other by crista terminallis.
The interior of right atrium also presents septal wall of the right atrium which has a shallow depression. fossa ovalis. Fossa ovalis:
is a shallow oval depression in the lower part of the interatrial septum.
marks the site of the foramen ovale, an opening in the interatrial septum of the fetal heart
represents septum primum
limbus fossa ovalis (free edge of septum secundum) forms the margins of fossa ovalis except inferiorly.
Enumerate the veins opening into the right atrium.
Following veins open into the right atrium:
Superior vena cava
Inferior vena cava
Coronary sinus
Anterior cardiac veins
Venae cordis minimae (Thebesian veins)
Describe the right atrioventricular orifice and tricuspid valve complex.
Right atrioventricular orifice
Is the opening between right atrium and ventricle.
Is elliptical in shape and about 3cm wide.
Is guarded by tricuspid valve.
Tricuspid valve complex
It guards the right atrioventricular orifice.
The complex includes:
Tricuspid annulus ( a collagenous ring to which the base of cusps are attached)
Three cusps :anterior, posterior and septal.
Chordae tendinae: Endothelial covered collagenous threads that connect the apical 1/3rd of the papillary muscles to the free margins and ventricular surface of the tricuspid valve complex.
Papillary muscles: are conical-shaped muscles , their base is attached to the walls of the ventricles and apex provide attachment to chordate tendinae. Right ventricle has three papillary muscles:
Anterior
Posterior
Septal
What is moderator band or septomarginal trabecula?
It is a specialized trabecula in the right ventricle that extends from the right side of the ventricular septum to the base of the anterior papillary muscle.
It carries the right branch of bundle of His.
It ensures the closure of right atrioventricular orifice before the systole so that there is no regurgitation of blood into the right atrium
It prevents over distension of right ventricle.
What are the differences between the right and left ventricle.
Applied Aspect
Fallot’s tetrology
Is a congenital heart anomaly which involves four anatomical abnormalities.
It is the most common cyanotic defect, and the most common cause of blue baby syndrome. The aorta and pulmonary artery develop from the truncus arteriosus which is divided by a spiral septum. The spiral septum separates the aorta and pulmonary artery and it grows down and attaches to the ventricular septum. However, if the spiral septum deviates towards the right side, following will happen:
opening to the pulmonary would be small
opening to the aorta would be large
spiral septum would not come in contact with the ventricular septum
As a result the following four defects will be present:
Pulmonary stenosis
Overriding aorta over the ventricular septal defect
Ventricular septal defect
Right ventricular hypertrophy
Right ventricular hypertrophy is a compensatory result due to pulmonary stenosis. As right ventricle has to work extra hard to pump blood into the pulmonary trunk, therefore it is hypertrophied.
Coronary arteries are:
highly enlarged vasa vasorum that supply the heart.
the only arteries that get filled up during diastole of the
heart.the only branches of ascending aorta.
functional end arteries i.e. the anatomical anastomosis
exist between the branches of coronary arteries,
however they are inadequate to compensate for the sudden
occlusion.
Describe the arterial supply of heart .
The heart’s arterial supply is derived from the right and left coronary arteries which are the branches of ascending aorta.
Right coronary artery
Origin: It arises from right ( anterior ) aortic sinus.
Course:
Passes forward between the pulmonary trunk and the right auricle.
Descends to the right in the atrioventricular sulcus (coronary sulcus).
Turns posteriorly at the junction of right and inferior border.
Continues along the posterior part of coronary sulcus to anastomose with the branch of left coronary artery.
Branches
Right conal artery
Artery to SA node (65% of cases)
Right marginal artery
Posterior interventricular branch –gives a branch to AV node ( 90% of cases).
Unnamed branches to right atrium and right ventricle
Areas supplied
Most of the right atrium.
Right ventricle except the area adjoining anterior interventricular groove.
Left ventricle adjacent to the posterior interventricular sulcus.
Posterior 1/3rd of the interventricular septum.
SA node in 65% of the cases.
AV node and bundle of His, except left branch of bundle of His.
Left coronary artery
Origin: It arises from left ( left posterior ) aortic sinus.
Course:
It passes first behind and then to the left of the pulmonary trunk to reach the left part of the atrio-ventricular sulcus
Divides into anterior inter-ventricular and circumflex branches
The circumflex branch represents the continuation of the left coronary artery and it turns round the left border of heart and continues along the posterior part of coronary sulcus to anastomose with the branches of right coronary artery.
Branches
Left conal artery
Anterior interventricular artery
Circumflex artery
Diagonal artery
Unnamed branches to left atrium and ventricle
Areas supplied
Left atrium
Left ventricle except the area adjoining posterior interventricular groove.
Right ventricle adjacent to the anterior interventricular sulcus.
Anterior 2/3rd of the interventricular septum.
SA node in 35% of the cases.
AV node in 10% of the cases.
Part of the left branch of bundle of His.
Describe briefly the ‘cardiac dominance’.
Coronary artery dominance: The artery which gives rise to the posterior interventricular artery (posterior descending artery (PDA) arises determines the coronary dominance.
If the posterior interventricular artery is a branch of right coronary artery then the coronary circulation is said to be “right-dominant”.
If the posterior interventricular artery arises from circumflex artery, a branch of the left artery, then the coronary circulation is “left-dominant”.
If the posterior interventricular artery arises from both the right coronary artery and the circumflex artery, then the coronary circulation is “co-dominant/balanced”.
Approximately 70% of the general population are right-dominant, 20% are co-dominant and 10% are left-dominant.
Applied Aspect
Angina Pectoris
Narrowing of coronary arteries is responsible for reduced blood flow which in turn results in decreased oxygen supply to cardiac muscle. The limited anaerobic metabolism of cardiac muscle results in built up of lactic acid which stimulates the pain receptors and as a result there is moderate to severe pain in the left precordium. The condition is called ‘angina pectoris’. The pain is often referred to left shoulder, ulnar side of left arm and forearm.
Cardiac pain due to angina pectoris or myocardial infarction is usually referred to the left precordium and medial aspect of left arm and forearm
The heart is innervated by upper four thoracic spinal segments (T1-T4). The skin over the precordium is supplied by T2-T4 spinal segments and the skin over the medial aspect of forearm and arm by T1 and T2 spinal segments respectively. The cardiac pain is therefore referred to the precordium and medial aspects of arm and forearm because of the same spinal segmental innervation.
Prognosis of coronary disease is better in old age than in young
The coronary arteries are functional end arteries but not anatomical end arteries. Anatomically the coronary arteries anastomose with each other by their trunks , branches and mostly at the precapillary level. In case of block in the coronary artery, as a result of thrombosis or atherosclerosis, these anastomoses are not effective in young people and as a result the coronary disease can be fatal in young. The coronary disease is less dangerous in old age because the anastomoses increase and collateral channels develop with the advancement of age.
Name the veins of heart.
WATCH VIDEO ON VENOUS DRAINAGE OF HEART [Click Here]
The venous blood from the heart is drained by three system of veins:
Coronary sinus : its tributaries are
great cardiac vein
middle cardiac vein
small cardiac vein
Oblique vein of left atrium
Anterior cardiac veins
Venae cordis minimae
Describe briefly Coronary sinus and its tributaries.
• Coronary sinus drains most of the venous blood from the heart.
• It is a short, wide venous cannel about 2.5cm. long and lies in the posterior part of the coronary sulcus.
• Its left end is continuous with the great cardiac vein.
• Its right end opens in the right atrium of the heart between the openings of inferior vena-cava and right atrioventricular orifice.
• Tributaries of coronary sinus
Great cardiac vein – it is the largest tributary of coronary sinus and lies along the anterior interventricular sulcus . It winds around the left margin of the heart and drains at the left end of the coronary sinus.
Middle cardiac vein – lies along the posterior interventricular sulcus. It joins the coronary sinus at its right end.
Small cardiac vein – it begin at the inferior border of the heart ( called right marginal vein) and then lies along the right posterior coronary sulcus. It drains in the coronary sinus at its right end.
Oblique vein of the left atrium or oblique vein of Marshall – it descends on the posterior wall of the left atrium and joins coronary sinus at its left end.
Posterior veinofleft ventricle-it lies on the diaphragmatic surface of left ventricle.
Which part of the heart is drained by Anterior cardiac veins and where do they open?
• Anterior cardiac veins are 2-3 small veins, that drain blood from the anterior aspect of right ventricle.
• They open into the right atrium.
What are venae cordis minimae?
Venae cordis minimae are very small veins present is each chamber of the heart.
They drain venous blood from the endocardium and deep part of myocardium.
They open directly into respective chamber of the heart.
What are the components of conducting system of heart?
Conducting system of heart is meant for initiating and maintaining cardiac rhythm and establish proper co-ordination between the atrial and ventricular contactions. It is made up of specialized cardiac muscle fibers having a high degree of sensitivity and autorhythmicity. Following are the components of conducting system:
1. Sinuatrial node (SA node)
Is also known as pacemaker.
Initiates the cardiac impulse.
Is located in the upper part of crista terminalis by the side of the opening of superior vena cava.
Impulse from SA node to AV node is carried by internodal fibers.
2. Atrioventricular node (AV node )
Is situated in the right atrium , in the lower part of interatrial
septum.It lies in the triangle of Koch, which is bounded by:
Base of septal cusp of tricuspid valve
Orifice of coronary sinus
Tendon of Todaro
3. Atrioventricular bundle of HIS
From the AV node the impulse travels in the atrioventricular bundle of HIS in the interventricular septum which divides into:
Right ventricular branch and
Left ventricular branch
The two branches descend in the interventricular septum and spread out in the walls of the respective ventricles to end as Purkinje fibers.
Describe briefly the nerve supply of heart.
The heart rate and the cardiac output are controlled by autonomic nervous system.
Sympathetic fibers are provided by the cardiac branches (preganglionic fibers) of superior, middle and inferior cervical ganglia (preganglionic fibers reach from T2-T5 spinal segments).
Parasympathetic fibers are provided by the cardiac branches (superior, inferior and recurrent) of the left & right vagus nerves.
The sympathetic and parasympathetic fibers reach heart via the superficial and deep cardiac plexuses.
Superficial cardiac plexus is located below the arch of aorta. it is formed by:
Cardiac branch of superior cervical ganglion of left sympathetic chain.
Inferior cervical cardiac branch of left vagus.
Deep cardiac plexus is located behind the arch of aorta and in front of tracheal bifurcation. It is formed by:
Cardiac branches of middle and inferior cervical ganglion of both the sympathetic chain and from the superior cervical ganglion of right sympathetic chain.
Cardiac branches of T2-T5 ganglion of both the sympathetic chain.
Superior and recurrent branches of both right and left vagus nerves and inferior cardiac branch of right vagus.
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