- Situated in the middle mediastinum
- Lies freely within the pericardium
- Pyramidal in shape
- Base lies posteriorly
- Apex is anterioinferior and points to left
- Three surfaces
- Strenocostal - formed by right atrium and ventricle and partly by
left ventricle and atrium
- Diaphragmatic - formed by right and left ventricles
- Base - formed by left atrium, to a lesser extent by the right
atrium
- Connected to the great vessels at the base
- Atrioventricular groove - separates the right and left atrium from
the ventricles
- Anterior and posterior interventricular grooves join each other
- Important relations of the heart included
- Laterally
- Phrenic nerves. Run adjacent to the pericardium
- Posteriorly
- Posterior mediastinal structures
- Oesophagus- behind the left atrium
- Descending thoracic aorta on left side
- Azygos vein on the right side
- Thoracic duct
Blood supply
Left coronary artery
- Arises from left posterior aortic sinus
- Passes behind the pulmonary trunk and then lies under the left
auricle
- Divides into anterior interventricular and circumflex branches
Anterior interventricular artery
- Also known as left anterior descending artery
- Continues in the anterior interventricular groove
- Anastomoses with the posterior interventricular branch of the right
coronary artery
- Gives the diagonal branch
Circumflex artery
- Winds (circumflexes) around the left heart border
- Passes in the atrioventricular groove
- Anastomoses with the right coronary artery Right coronary artery
- Arises from anterior aortic sinus
- Passes between the pulmonary trunk and the right atrium
- Traverses the atrioventricular groove
- Ends by anastomosing with the branches of circumflex artery
- Branches include
- To the sino-atrial node
- To left atrium
- Right marginal artery
- Posterior interventricular artery (also known as posterior
descending artery)
“Dominance” of the coronary circulation
- Right dominance
- Posterior interventricular artery arises from the right coronary
artery
- Left dominance
- Posterior interventricular artery arises from left coronary artery
(10%)
- Codominant
- Posterior interventricular artery formed by both right and left
coronary arteries (10%)
Blood supply to the conducting system of the heart
- SA node - branch from right coronary artery in 60% of the population
- AV node - from posterior interventricular artery
Venous drainage
Coronary sinus
- Receives most of the blood
- Lies in the posterior part of the atrioventricular groove
- Opens into the right atrium
- Is a continuation of the great cardiac vein
- Tributaries included middle and small cardiac vein
Anterior cardiac vein
- Open directly into the right atrium Venae cordae minimae
- Drain directly into the chambers of the heart
Nerve supply of the heart
- Sympathetic
- Cervical and upper thoracic portions of the sympathetic chain
through the stellate ganglion
- Afferent fibres running with the sympathetic fibres conduct pain
- Parasympathetic
- The sympathetic and parasympathetic nerves form cardiac plexuses
- Superficial cardiac plexus lies in front of the right pulmonary
artery
- Deep cardiac plexus lies in front of the tracheal bifurcation
Conduction system
Sinoatrial node
- Located in the wall of the right atrium just to the right of the
opening to the superior vena cava
- This node gives a spontaneous impulse that spreads in all directions
through the myocardium of the atria
- This causes the atrial muscle to contract.
Atrioventricular node
- Located on the lower part of the atrial septum, just above the
tricuspid valve.
- Activated by the excitation wave that passes through the atria from
the SAN.
- From this the impulse moves to the atrioventricular bundle, where it
moves on down through the ventricles
Atrioventricular bundle
- It is usually known as the Bundle of His
- It is the only pathway of cardiac muscle that connects the
myocardium of the atria and the myocardium of the ventricles
- It is the only route the impulse can travel down
- It descends through the fibrous skeleton of the heart.
- At the bottom of the membranous part of the ventricular septum it
divides into two branches, one for each ventricle.
- The right bundle branch travels down the right ventricle wall and
joins the Purkinje fibres
- The left bundle branch travels down the left ventricular wall
- Usually splits into anterior and posterior branches then joins the
Purkinje fibres
Purkinje fibres
- Lots of cross linking strands.
- Covers the whole ventricle wall.
- Ensures that the whole of each ventricle contracts at once to
efficiently pump blood.
Pericardium
- Fibro-serous layer enclosing the heart and roots of great vessels
- Outer fibrous
- Inner serous is as double layered
- Has inner visceral layer and outer parietal layer
- Both layers continuous around the great vessels and the pulmonary
veins
- This leads to the formation of the pericardial sinuses
Pericardial sinuses
- Two in number - oblique sinus and transverse sinus
- Lie on the posterior surface of the heart
|