Coronary arteries supply the myocardium with oxygenated blood.

Right coronary artery:

• Arises directly from the right side of the aorta (specifically, from the right aortic sinus) and travels posteriorly within the coronary sulcus.
• Branches:
  • Sinoatrial nodal branch (aka, sinoatrial nodal branch).
  • Right marginal branch.
  • Posterior interventricular branch (aka, the PDA, posterior descending artery), which travels within the posterior interventricular groove (aka, sulcus).

Left coronary artery:

• Arises directly from the left side of the aorta and travels posteriorly within the coronary sulcus (the left coronary artery is sometimes referred to as the left main stem vessel).
• Branches:
  • Circumflex artery, which gives off the left marginal artery.
  • Anterior interventricular branch (aka, the LAD, left anterior descending artery), which travels within the anterior interventricular groove (aka, sulcus).

Areas served by the right coronary artery:

• The right atrium
• Most of the right ventricle
• The sinoatrial node (in 60% of individuals)
• The atrioventricular node (in 80% of individuals)

Areas served by the left coronary artery:

• Left atrium
• Most of the left ventricle
• Most of the interventricular septum
• The sinoatrial node (in 40% of individuals)

Three common patterns of arterial supply:

• Right-dominant pattern, in which the posterior interventricular artery branches from the right coronary artery; this is the most common pattern.
• Left-dominant pattern, in which the posterior interventricular artery branches from the left coronary artery; this is less common.
• Codominance, in which both the right and left coronary arteries contribute to the posterior interventricular artery.
• Occasionally, individuals will have only one coronary artery, or will have accessory coronary arteries.

Additional Information:

• In general, the coronary arteries are functional end vessels, which means that there is little to no redundancy in the blood supply of the myocardium.

• Two common exceptions to this rule:
  • Anastomoses between the anterior and posterior interventricular arteries
  • Anastomoses between the right and left coronary arteries

• Anastomoses provide alternative pathways, called collateral channels, through which oxygenated blood can reach the myocardium.

Clinical correlations:

• Occlusion (aka, blockage) of a coronary artery can cause ischemia and myocardial infarction (heart attack).
  • Treatments for coronary artery occlusion include:
    Coronary angioplasty, in which the clogged artery is widened at the site of the obstruction.
    Coronary artery bypass graft surgery, in which vascular segments from elsewhere in the body (eg, the great saphenous vein, internal thoracic arteries, or radial arteries) are grafted to the heart to circumvent the obstructed coronary arteries.

Endocardium

• Innermost layer of heart wall
• Endocarditis (inflammation of the endocardium) can destroy the valves and disrupt blood flow through the heart.

Myocardium

• Cardiac muscle fibers (cells) are anchored to the dense regular connective tissue of the fibrous skeleton. In addition to anchoring the cardiac muscle fibers, the fibrous skeleton maintains the structural and physiological integrity of the heart.
• The myocardial layer is injured in myocardial infarction (aka, heart attack), which occurs when obstructed coronary artery blood flow causes cardiac muscle cell death.

Epicardium

• Most superficial layer of heart wall
• Often filled with fat
• Two sublayers; outermost layer is visceral layer of pericardium.

Pericardium:

Fibrous layer

• Most superficial layer
• Tough layer of dense connective tissue
• Because it is inelastic, it prevents overfilling of the heart.
• Arises from the diaphragm
• Covers the heart and the roots of the great vessels, with which it is continuous

Serous layer

• Parietal layer:
  Lines the fibrous pericardium
• Pericardial cavity
  Between parietal and visceral layers; contains thin layer of fluid to reduce friction and allow movement of heart
• Visceral layer
  Forms most superficial layer of the epicardium

Pericarditis (inflammation of the pericardium) causes the pericardium to rub against the heart, which causes friction. As a result, patients experience pain and can even suffer from impaired heart function, which, sometimes necessitates medical or surgical intervention.

Base of heart

Located posteriorly, widest part of heart

Apex of heart

Located inferiorly, narrowest part of heart, points towards left side of body

4 Chambers of the heart:

Left and Right Atria, superiorly

• Auricles are ear-like extensions of the atria; expand to accommodate blood flow
• Superior and inferior vena cavae return blood to right atrium
• Pulmonary veins return blood to left atrium

Left and Right Ventricles, inferiorly

• Anterior and posterior interventricular sulci separate right from left
• Aorta carries blood away from left ventricle
• Pulmonary trunk carries blood away from right ventricle

Coronary sulcus (aka, atrioventricular groove)

Groove between the atria and ventricles where coronary vessels travel.

Key Features of the Internal Heart:

• The right side of the heart receives deoxygenated blood from the body and sends it to the lungs.
• The left side of the heart receives oxygenated blood from the lungs and sends it to the body.

Septi (singular = septum)

• Structurally and functionally divide the heart into right and left sides; each side operates as a muscular pump.
  • Interventricular septum divides right and left ventricles, inferiorly.
  • Interatrial septum divides right and left atria, superiorly.

Chambers

• Atria
  • Superior chambers
• Ventricles
  • Inferior chambers

Valves

• Ensure unidirectional blood flow through the heart.

Right atrioventricular valve

• Three cusps (aka, leaflets):
  • Anterior
  • Posterior
  • Septal
• Because it has three cusps, this valve is called the “tricuspid valve.”

Left atrioventricular valve

• Two cusps:
  • Anterior
  • Posterior
• Because it has two cusps, it is called the bicuspid valve (aka, the mitral valve, because it is mitre-shaped).

Semilunar valves:

• Aortic and pulmonary semilunar valves ensure that blood travels from through the aorta and pulmonary trunk unidirectionally.

Papillary muscles

• Anchor AV valves.
• Special extensions of the trabeculae carneae in the ventricles (papillary refers to their nipple-like shape).
• The moderator band (aka, septomarginal trabecula) spans from the interventricular septum to the base of the anterior papillary muscle; it prevents the ventricle from overfilling, and contains a portion of the cardiac conduction system (which is addressed in a separate tutorial).

Right ventricle has three papillary muscles, each named for its location:

• Anterior
• Posterior
• Septal (which is sometimes absent)

Left ventricle typically has two papillary muscles

• Anterior
• Posterior

Chordae tendineae

• Short cords that attach flaps of valves to papillary muscles to prevent prolapse (aka, eversion) of the valves, and ensure unidirectional blood flow through the chambers.

Features of the Ventricles:

• Walls of the left ventricle are more muscular and thicker than the walls of the right.
  • The left ventricle must produce more muscular force to pump blood to the body; in contrast, the right ventricle produces less force, as it sends blood to the nearby lungs.
• Trabeculae carnae
  Irregular ridges of muscle on internal ventricular surface

Features of the Atria:

• Pectinate muscles line the anterior wall of the right atrium. These muscles also exist in the left atrium but are less abundant.
• Fossa ovalis is a shallow depression in the wall of the interatrial septum.
  • The fossa ovalis is clinically significant from the moment of birth, when it seals off an opening in the interatrial septum called the foramen ovale.
  • In utero, the foramen ovale shunts blood directly from the right to left atrium, which allows the blood to bypass the nonfunctional lungs (the fetus receives oxygen directly from the maternal blood via the placenta).
    Immediately after birth, the interatrial septum fuses, which closes the foramen ovale; the fossa ovalis represents this fusion.
  • In some cases, septal fusion is incomplete (aka, patent foramen ovale), which can impede blood flow and, consequently, blood oxygenation.

Great vessels

• Arteries send blood away from the heart
• Veins return blood to the heart

Aorta

• Arises from the left ventricle and arches posteriorly; carries oxygenated blood away from the left ventricle.

Pulmonary trunk

• Arises from the right ventricle and splits to form the right and left pulmonary arteries; pulmonary arteries carry deoxygenated blood away from the right ventricle, to the lungs.

Pulmonary veins

• Drain into the left atrium; return blood to the heart from the lungs. (“pulmonary” refers to the lungs”).

Inferior and Superior vena cavae

• Return deoxygenated blood from the body to the right atrium

Opening of coronary sinus

• Returns deoxygenated blood from the myocardium to the heart to right atrium.