Thoracic Cavity: Pericardium and Heart

• The thoracic cavity includes the pericardium and heart.

Lecture Objectives

• Locate the pericardium and heart in the human body.
• Distinguish the surfaces of the heart.
• Relate the structures of the heart's chambers to their functions.
• Track the route of blood flow.
• Integrate the blood supply, venous drainage, and nerve supply relative to location and function.
• Explain the conducting system of the heart.
• Summarize the large arteries and veins of the thorax.

Pericardium

• Located within the middle mediastinum.
• It is a fibroserous sac that encloses the heart and the roots of the great vessels.
• Functions to restrict excessive movements of the heart and serve as a lubricant during contraction.

Pericardium Boundaries

• Anterior Boundary: Body of the sternum and the 2nd to 6th costal cartilages.
• Posterior Boundary: T5 to T8 vertebrae.

Fibrous Pericardium

• Sternopericardial ligaments attach it to the sternum.
• It is firmly attached to the insertion of the diaphragm.
• Fuses with outer coats of the aorta, pulmonary trunk, superior & inferior vena cava, and pulmonary veins.

Serous Pericardium

• Parietal Layer: Lines the fibrous pericardium and reflects around the roots of the great vessels.
• Visceral Layer: Closely applied to the heart and commonly called the "Epicardium".
• Pericardial Cavity: This is a slitlike space between the layers that contains pericardial fluid.

Pericardial Sinuses

• Reflections of serous pericardium around the great blood vessels.

Transverse Sinus Location

• Anterior to the superior vena cava.
• Posterior to the ascending aorta and pulmonary trunk.

Oblique Sinus Boundaries

• Posterior to the heart in the pericardial sac.
• Right boundary: Inferior vena cava and the right pulmonary veins.
• Left boundary: Left pulmonary veins.

Nerve Supply of the Pericardium

• Phrenic Nerves: Innervate the fibrous pericardium and parietal layer of the serous pericardium.
• Vagus Nerves and Sympathetic Trunks: Innervate the visceral layer of the serous pericardium.

Surfaces of the Heart

• Sternocostal (anterior)
• Diaphragmatic (inferior)
• Base (posterior)
• Apex: Points downward and forward to the left.

Sternocostal (Anterior) Surface

• Formed mainly by the right atrium and right ventricle.
• Includes a Vertical Atrioventricular groove and Anterior Interventricular groove.
• It also touches the left ventricle and left auricle.

Diaphragmatic (Inferior) Surface

• Formed mainly by the right and left ventricles and includes the Posterior Interventricular groove.
• It also touches the inferior surface of the right atrium (IVC).

Base (Posterior) of the Heart

• Formed mainly by the left atrium, opposite the apex.

Apex of the Heart

• This consists of the left ventricle at the level of the 5th intercostal space.
• Located 3.5 inches or 9 cm from the midline.

Atrial Septum

• Divides the thin-walled atria.
• Runs from the anterior wall of the heart backward and to the right.

Ventricular Septum

• Placed obliquely with one surface facing forward to the right and the other facing backward to the left.

Right Atrium

• Crista Terminalis: Vertical ridge running from the SVC to the IVC.
• Sulcus Terminalis: This is a groove on the exterior of the heart that corresponds to crista terminalis.

Right Atrium Smooth and Rough Walls

• Posterior to the Ridge: Smooth walled, derived from the sinus venosus.
• Anterior to the Ridge: Roughened by musculi pectinati, derived from the primitive atrium.

Openings in the Right Atrium

• Superior Vena Cava: lacks a valve, returns blood from the upper body.
• Inferior Vena Cava: Guarded by a rudimentary, nonfunctioning valve and it returns blood from the lower half of the body and is larger than the SVC.
• Coronary Sinus: Drains most of the blood from the heart wall and is between the IVC and atrioventricular orifice, guarded by a rudimentary, nonfunctioning valve.
• Right Atrioventricular Orifice: Anterior to the inferior vena caval opening and is guarded by the tricuspid valve.

Fetal Remnants

• Located on the atrial septum.
• Fossa Ovalis: Site of the foramen ovale in the fetus.
• Anulus Ovalis: Upper margin of the fossa.

Right Ventricle

• Trabeculae Carneae: Internal projecting ridges formed by muscle bundles.
• Three types of Trabeculae Carneae include Papillary Muscles (Chordae Tendinae), Moderator band, and Prominent ridges.

Papillary Muscles

• Bases are attached to the ventricular wall.
• Apexes are connected to cusps of the tricuspid valve by chordae tendinae.

Moderator Band

• Crosses the ventricular cavity from the septal to the anterior wall.
• This conveys the right branch of the AV bundle.

Tricuspid Valve

• 3 cusps: Anterior, Septal, and Posterior.
• Bases are attached to the fibrous ring of the skeleton of the heart.
• Free edges attached to chordae tendinae.

Pulmonary Valve

• Guards the pulmonary orifice.
• Curved lower margins attached to the arterial wall.
• Open mouths of cusps directed upward into the trunk.
• Consists of 3 semilunar cusps.

Left Atrium

• Has four pulmonary veins with no valves and a left atrioventricular orifice (mitral valve).

Left Ventricle

• Openings: Aortic orifice and left atrioventricular orifice.
• Walls are 3x thicker than the right ventricle.
• Cross section: Circular; the right ventricle is crescentic.

Mitral Valve

• Guards the left atrioventricular orifice.
• Has 2 cusps: anterior and posterior.

Aortic Valve

• Guards the aortic orifice.
• Has 3 cusps: Right/Anterior, Left and Posterior cusps.
• Right aortic sinus: Origin to right coronary artery.
• Left aortic sinus: Origin of the left coronary artery.

Arterial Supply of the Heart

• Right Coronary Artery: Supplies the right atrium, right ventricle, parts of the left atrium and left ventricle, and atrioventricular septum.
• Left Coronary Artery: Supplies the major part of the heart (greater part of the left atrium and left ventricle) and the ventricular septum.
• Divides into an anterior descending branch and circumflex branch.

Branches of the Right Coronary Artery

• Right Conus artery.
• Anterior ventricular branches.
• Marginal branch.
• Posterior ventricular branches.
• Posterior interventricular (descending) artery.
• Septal branch for AV node.
• Atrial branches.
• Artery of the SA node.

Branches of the Left Coronary Artery

• Anterior interventricular (descending) branch.
• Left diagonal artery.
• Left conus artery.
• Circumflex artery.
• Left marginal artery.
• Anterior ventricular branch.
• Posterior ventricular branch.
• Atrial branches.

Conducting System of the Heart

• Normal Heart Rate: 70-90 beats per minute.
• Atria contract first, then ventricles after a slight delay.
• SA Node to AV Node to AV Bundle to Purkinje Fibers.

Sinoatrial Node (SA)

• Pacemaker of the heart.
• Located in the wall of the right atrium on the upper part of the sulcus terminalis and to the right of the opening of the SVC.

Atrioventricular Node (AV)

• In the lower part of the atrial septum just above the attachment of the septal cusp of the tricuspid valve.

AV Bundle/Bundle of His

• Connects the myocardium of the atria and the myocardium of the ventricles.
• Divides into 2 branches: right and left bundle branches.

Right Bundle Branch (RBB)

• Reaches the moderator band.

Left Bundle Branch (LBB)

• Pierces the septum and divides into anterior and posterior branches.

Purkinje Fibers

• RBB and LBB become continuous.
• Influenced by autonomic nerve supply.
• Parasympathetic (PNS): Slow rhythm.
• Sympathetic (SNS): Fast rhythm.

Nerve Supply of the Heart

• Sympathetic = Cervical and upper portions of the sympathetic trunks, terminating on the SA and AV nodes, cardiac muscle fibers, and coronary arteries. Cardiac acceleration, increased forced contraction, and vasodilation.
• Parasympathetic = This arises from Vagus Nerves to SA and AV nodes, coronary arteries. Reduction in rate and force of contraction, and vasoconstriction.

Large Arteries of the Thorax

• Ascending Aorta: Right and left coronary arteries.
• Arch of the Aorta: Brachiocephalic, Left Common Carotid, and Left Subclavian arteries.
• Descending Aorta: Posterior Intercostal, Pericardial, Esophageal, and Bronchial arteries.

Pulmonary Trunk

• Right pulmonary artery.
• Left pulmonary artery.

Ligamentum Arteriosum

• Fibrous band that connects the bifurcation of the pulmonary trunk to the aortic arch; this remains of the ductus arteriosus.

Large Veins of the Thorax

• Union of subclavian vein and internal jugular vein.