Blood Supply and Conducting System of Heart

Heart – Blood Supply and Conducting System

Learning Objectives

After reading this post you will know:

  • Characteristic features of coronary arteries.
  • Arterial supply of heart.
  •  Origin, course and branches of right and left coronary arteries.
  • Parts of heart supplied by right and left coronary arteries.
  • Venous drainage of heart.
  • Tributaries of coronary sinus.
  • Conducting system of heart.
  • Nerve supply of heart.

Q. What are the characteristic features of coronary arteries?coronary arteries
A. 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.

 

Q. Describe the arterial supply of heart.
A. The heart’s arterial supply is derived from the right and left coronary arteries which are the branches of
ascending aorta.
a. 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

o Right conal artery
o Artery to SA node (65% of cases)
o Right marginal artery
o Posterior interventricular branch –gives a branch to AV node ( 90% of cases).
o Unnamed branches to right atrium and  right ventricle

Areas supplied

o Most of the right atrium.
o Right ventricle except the area adjoining anterior interventricular groove.
o Left ventricle adjacent to the posterior interventricular sulcus.
o Posterior 1/3rd of the interventricular septum
o SA node in 65% of the cases.
o AV node and bundle of His, except left branch of bundle of His.

arterial supply of heart - coronary arteries

b. Left coronary artery
Origin: It arises from left ( left posterior ) aortic sinus.
Course: 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 -> 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

o Left conal artery
o Anterior interventricular artery
o Circumflex artery
o Diagonal artery
o Unnamed branches to left atrium and ventricle

Areas supplied

o Left atrium
o Left ventricle except the area adjoining posterior interventricular groove.
o Right ventricle adjacent to the anterior interventricular sulcus.
o Anterior 2/3rd of the interventricular septum
o SA node in 35% of the cases.
o Part of the left branch of bundle of His.

 

Q. Describe briefly the ‘cardiac dominance’.
A. Coronary artery dominance: The artery from which 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.

cardiac dominance

 

Q. Give anatomical basis of the following:
a. Angina pectoris
b. The cardiac pain due to angina pectoris or myocardial infarction is usually referred to the left precordium
and medial aspect of left arm and forearm.

c. Prognosis of coronary disease is better in old age than in young.

A. a.  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.

referred pain in agina pectoris or myocardial infarction

b. 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.

c. 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.

Q. Describe briefly:
a. Venous drainage of the heart.
b. Conducting system of the heart.
c. Nerve supply of heart

A. a.  Venous drainage of heart

The venous blood from the heart is drained by three system of veins:
i. Coronary sinus
ii. Anterior cardiac veins
iii. Venae cordis minimae

i. Coronary sinus:

• Drains most of the venous blood from the heart.
• Is a short , wide venous cannel about 2.5cm. longnand lies in the posterior par 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.

• Tributariesvenous drainage of heart

Great cardiac vein – lies along anterior interventricular sulcus
Middle cardiac vein –  lies along the posterior interventricular sulcus
Small cardiac vein –lies along  right posterior coronary sulcus
Right marginal vein – along the inferior  boder
Oblique vein of the left atrium
Posterior ventricular vein

ii. Anterior cardiac veins

• Several small veins , that drain blood from the anterior aspect of right ventricle.
• They open into the right atrium.

iii. Venae cordis minimaevenae cordis minimae

• Drain venous blood from the endocardium and deep part of
myocardium.
• Open directly into the every chamber of  the heart.

 

 

b. Conducting system of the heartconducting system of heart

• It is meant for initiating and maintaining cardiac rhythm and establish proper co-ordination between the atrial
and ventricular contactions.
• Is made up of specialized cardiac muscle fibers having a high degree of sensitivity and autorhythmicity.

Components:
o 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 intermodal fibers.

o Atrioventricular node (AV node )triangle of kosch

 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

o Atrioventricular bundle of HIS

 From the AV node it descends in the interventricular septum and divides into:

• Right ventricular branch
• 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.

c. 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 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.
    o The 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.
    o The 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 the vagi and inferior cardiac branch of right vagus.

 

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