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1. Describe the pericardium.

The pericardium is a sac that surrounds and protects the heart, and provides it with sufficient space to expand (during diastole). The pericardium consists of two layers: an outer, fibrous pericardium, and an inner, serous pericardium.

The fibrous pericardium is a tough layer of dense connective tissue, which anchors the pericardium to the diaphragm and surrounding structures. The fibrous pericardium is inflexible, and prevents the heart from overfilling during diastole.

The serous pericardium is a relatively delicate, contiguous mesothelial sac, which nearly completely envelops the heart. The superficial portion of the serous pericardium which fuses to the fibrous pericardium is known as the parietal pericardium. The deep portion of the serous pericardium which fuses directly to the heart is known as the visceral serous pericardium (i.e. the epicardium). Between the parietal and visceral pericardial layers is a potential space, the pericardial space, which contains a small amount of pericardial fluid to reduce friction.

2. Describe the functions and locations of the four chambers of the heart, and understand basic terminology regarding the cardiac cycle, valve function, and heart sounds.

The heart is an ever working pump to distribute blood to the lungs (pulmonary circulation) and metabolically active tissues (systemic circulation) of the body. The heart is found in the middle mediastinum of the thoracic cavity, surrounded by the pericardium. 

There are 4 chambers of the heart: right & left atria and right & left ventricles.

• Atria: receive venous blood that will be pumped into ventricles; weak contraction

  • Right atrium: receives de-oxygenated blood from the superior vena cava (SVC), inferior vena cava (IVC), coronary sinus, and anterior cardiac vv.

    • Pumps de-oxygenated blood into R. ventricle (through R. atrioventricular orifice)

  • Left atrium: receives oxygenated blood from the pulmonary vv. (from lungs)

    • Pumps oxygenated blood into L. ventricle (through L. atrioventricular orifice)

• Ventricles: discharge blood either into pulmonary trunk (from R. ventricle) or ascending aorta (from L. ventricle); more powerful contraction

  • Right ventricle: receives de-oxygenated blood from R. atrium

    • Pumps de-oxygenated blood through the pulmonary trunk/arteries to the lungs (through pulmonary/semilunar valve)

  • Left ventricle: receives oxygenated blood from L. atrium

    • Pumps oxygenated blood through the ascending aorta to the rest of the body (through aortic/semilunar valve)

Often the heart is divided into right and left parts, based on the composition of blood. These parts work at the same time and rate, with similar amounts of blood.

• Right heart (R. atrium and ventricle)

  • Relatively de-oxygenated blood

  • Pulmonary circulation

• Left heart (L. atrium and ventricle)

  • Oxygenated blood

  • Systemic circulation

Terms to be familiar with:

• Diastole: relaxation

  • Ventricles fill with blood

• Systole: contraction; typically associated with ventricles contracting (ventricular systole)

  • Ventricles empty blood into aorta & pulmonary trunk

• Heart sounds: created by the shutting of valves (to prevent backwards flow)

  • Lub (1st sound; S1)

    • Atrioventricular (AV) valves closure

    • loudest at the apex

  • Dub (2nd sound; S2)

    • Aortic & pulmonic valve closure

    • loudest at base

3. Describe the external features of the heart, including which chambers of the heart compose the surfaces and borders.

There are 4 borders of the heart:

• Right border: portion of the heart located between the superior and inferior venae cavae

  • Formed by R. atrium

• Left border (obtuse margin): formed predominantly by the L. ventricle with a small contribution from the L. auricle of the L. atrium

• Superior (upper) border: formed by the R. and L. atria

  • This border is important in terms of the close relationship to large vascular structures, such as the ascending aorta, pulmonary trunk, and superior vena cava

• Inferior border (acute margin): formed predominantly by the R. ventricle with a contribution from the L. ventricle

There are 6 surfaces or aspects of the heart, including the apex and base:

• Sternocostal (anterior) surface: formed predominantly by the R. ventricle with small contributions from the R. atrium & L. ventricle

  • The coronary & anterior interventricular sulci are visible on this surface

• Apex of the heart: formed by the L. ventricle

  • Often considered as anteriorly facing and directed to the left

  • Located near the L. midclavicular line, just deep to the L. 5th intercostal space

• Right surface: formed by R. atrium

• Left surface: formed mainly by the L. border of the heart

• Diaphragmatic (inferior) surface: formed mainly by the L. ventricle and portions of the R. ventricle

  • Very closely associated with the diaphragm

• Base of heart (posterior aspect of heart): formed predominantly by the L. atrium with some contribution from the R. atrium

  • Closely associated with the pulmonary vv. & oblique pericardial sinus

  • Often considered as posteriorly facing and directed more to the right

There are 3 sulci (grooves) of the external heart that are superficial artifacts of the divisions/walls of the heart:

• Coronary (atrioventricular) sulcus: sulcus between the atria and ventricles

  • Contains the coronary sinus, R. & L. coronary aa., main trunks

• Anterior interventricular (IV) sulcus: sulcus between the ventricles; continuous with posterior interventricular sulcus

  • Located on sternocostal (anterior) surface

  • Anterior interventricular br. (left anterior descending - LAD) of L. coronary a. & great cardiac v. are located in this sulcus

• Posterior interventricular (IV) sulcus: sulcus between the ventricles; continuous with the anterior interventricular sulcus

  • Located mostly on the diaphragmatic surface

  • Posterior interventricular br. (posterior descending a.) of R. coronary a. & middle cardiac v. are located in this sulcus

4. Conceptualize the three layers of the heart wall.

There are three layers of the heart wall (from superficial to deep):

• Epicardium (visceral serous pericardium)

  • May be difficult to separate from the deep epicardial fat

    • Epicardial fat is varied in amount and distribution, but tends to collect in the coronary sulcus, anterior & posterior interventricular sulci, and around the origins of the great vessels

• Myocardium

  • Cardiac muscle

    • Majority of the heart wall and varies in thickness

• Endocardium

  • Internal layer of endothelium and connective tissue which lines internal chambers and valves

6. Identify the unique structures of the right ventricle.

Right atrioventricular (tricuspid) valve

• Composed of 3 valve cusps which attach to the fibrous ring surrounding the right AV orifice

  • Cusps are drawn together before R. ventricular contraction, thus preventing the retrograde flow of blood from the R. ventricle to the R. atrium, and to direct the flow of blood through the pulmonary valve

  • Close during systole; open during diastole

• Chordae tendineae: thin cords that attach to neighboring valve cusps from an origin of the papillary muscles; prevent prolapse

• Papillary muscles: three extensions of myocardium, which attach to chordae tendineae for each cusp of the tricuspid valve

  • Anterior, posterior, and septal papillary muscles

  • Anterior papillary muscle is the largest

Septomarginal trabecula (moderator band): a specialized bundle of trabecular muscle that is located between the base of the anterior papillary muscle and the inferior portion of the interventricular septum

• A portion of the R. atrioventricular (AV) bundle is located within this muscle

Trabeculae carneae: muscle elevations (beams, ridges) located on ventricular walls

Interventricular (IV) septum: located between the R. and L. ventricles

• Composed of muscular (predominantly) and membranous parts

Conus arteriosus: a relatively smooth (and cone-shaped) portion of the wall leading into the pulmonary trunk

Pulmonary valve

• This valve is located between the R. ventricle and the pulmonary trunk

• Has three, semilunar cusps (anterior, right, and left)

• When blood is pumped through the R. ventricle into the pulmonary trunk, the cusps project into the trunk

  • When relaxation of the ventricle occurs, the cusps meet (‘snap close’) to prevent blood from returning to the ventricle

• Close during diastole; open during systole

7. Identify the unique structures of the left atrium.

The left atrium receives the pulmonary veins from the lungs.

Auricle (appendage): muscular pouch that is located in the superior, left border (often overlapping the root of the pulmonary trunk)

• Internally, has pectinate muscles

  • Only area of the internal L. atrium with pectinate muscle (the rest is mostly smooth-walled)

L. atrioventricular (mitral) valve orifice

• The L. AV valve is located between the L. atrium and L. ventricle

Interatrial septum

• Wall between the R. and L. atrium

Semilunar depression: a small depression in the interatrial septum that represents the floor of the fossa ovalis

8. Identify the unique structures of the left ventricle.

L. atrioventricular (mitral, bicupsid) valve

• Composed of two valve cusps (anterior & posterior) which attach to the fibrous ring surrounding the left AV orifice

  • Cusps are drawn together before L. ventricular contraction, thus preventing the retrograde flow of blood from the L. ventricle to the L. atrium, and to direct the flow of blood through the aortic valve

  • Close during systole; open during diastole

• Chordae tendineae: thin cords that attach to neighboring valve cusps from the papillary muscles

• Papillary muscles: two muscles that attached to the ventricular wall

  • Anterior & posterior papillary muscles

Trabeculae carneae: numerous in the L. ventricle

• The heart walls of the L. ventricle are significantly thicker than in the R. ventricle due to the higher arterial pressure associated with systemic circulation

Aortic vestibule: smooth-walled portion of the L. ventricle leading into the aortic orifice

Aortic orifice: at the orifice, there is a transition from ventricle to ascending aorta

Aortic (semilunar) valve

• Has three, semilunar cusps (posterior, right, and left)

• Close during diastole; open during systole

• When blood is pumped through the L. ventricle into the ascending aorta, the cusps project into the trunk

  • When relaxation of the ventricle occurs, the cusps meet (‘snap close’) to prevent blood from returning to the ventricle

  • Aortic sinuses (of Valsalva): dilations of the ascending aorta just superior to the cusps of the aortic valve (there are also sinuses of the pulmonary trunk)

    • The right coronary a. (RCA) and the left coronary a. (LCA) originate in the upper portions of the R. and L. aortic sinuses, respectively

9. Describe the arterial supply of the heart by diagraming the pathways and branches of the left and right coronary arteries.

The epicardium and myocardium are supplied by the right and left coronary aa. (RCA & LCA), which are the first (most proximal) branches of the ascending aorta.

Right coronary a. (RCA):

• Originates in the right aortic sinus (of Valsalva)

• Typically travels between the ascending aorta and the R. auricle as it enters the coronary sulcus

• Branches include:

  • Sinu-atrial (SA) nodal br.: branches near the ascending aorta toward the SA node located near the junction of the R. atrium and superior vena cava

    • A branch of the RCA in 60% of individuals

    • In 40% of cases, it is a branch of the circumflex br. of the LCA (Moore et al., 2014)

  • R. marginal br.: located along the inferior border of the heart and is typically the last anterior branch of RCA

  • Atrioventricular (AV) nodal br.: arises near the posterior interventricular br., and dives deep and superior toward the AV node

    • Arises from RCA in 67% of individuals, and circumflex br. of LCA in 33% of cases

  • Posterior interventricular (posterior descending) br.: located in posterior interventricular sulcus

    • Arises from RCA in 67% of individuals, and circumflex br. of LCA in 33% of cases

    • Heart dominance

      • Determined by which coronary artery supplies the crux of the heart (e.g. the origin of the posterior interventricular branch, but also the AV nodal br.)

        • Right dominance = source is RCA

          • Typical

        • Left dominance = source is LCA

        • Codominance = source is both RCA and circumflex branch of LCA

Left coronary artery (LCA): located between the pulmonary trunk and L. auricle as it enters the coronary sulcus

• Branches include:

  • Anterior interventricular (left anterior descending) br.: located in the anterior interventricular sulcus

    • Typically anastomoses with posterior IV br.

    • The most common site of artery occlusion in the heart

  • Circumflex br.

    • Often referred to as a continuation of the LCA, continuing through the coronary sulcus to the base of the heart (posterior aspect)

    • L. marginal a., follows the left border of the heart

    • In left and/or codominant hearts:

      • AV nodal br

      • Posterior interventricular brs.

10. Describe the venous drainage of the heart.

Venous drainage of the heart may be divided into two systems:

• Greater system, consisting of named tributaries, mostly coalescing in the coronary sinus, which delivers blood to the right atrium, and the

• Smaller system, consisting of small cardiac (Thebesian) veins that drain the subendocardial myocardium directly into each chamber. 

Coronary sinus: located in the coronary sulcus and most veins of the heart drain here

• Tributaries include:

  • Great cardiac v.: typically the largest tributary of the coronary sinus

    • Travels next to the anterior IV a. in the anterior IV sulcus

    • Part of the vein travels in the coronary sulcus with the circumflex br. of the LCA to eventually drain into the coronary sinus

  • Middle cardiac v.: travels within the posterior IV sulcus with the posterior IV br. of the RCA to drain into the coronary sinus

  • Small cardiac v.: typically visible near the inferior border of the heart, near the R. marginal br. of the RCA

Anterior cardiac vv.: unique among cardiac vv. in that they typically drain directly into the R. atrium, rather than into the coronary sinus

• Travel superficially over the RCA from the R. ventricle to the R. atrium

The smaller system (Thebesian veins) are most dense in association with the right atrium, and least dense around the left ventricle. 

11. Compare how systemic and pulmonary circulations are structured. 

Systemic circulation delivers blood from the left ventricle of the heart to metabolically active tissues by means of the aorta and its branches, and returns blood to the right atrium of the heart by means of the caval system (superior and inferior vena cavae and their tributaries). Pulmonary circulation delivers blood relatively rich with CO2 and low in O2 from the right ventricle of the heart to the lungs by means of the pulmonary trunk, pulmonary arteries, etc., and returns richly oxygenated blood to the left atrium.

12. Identify the locations of major components of the conductive system of the heart.

There are two main types of structures associated with the electrical conduction system of the heart: nodal tissue and conducting fibers. Nodal tissue is responsible for initiating impulses (autorhythmic) that lead to contraction of the heart. The nodal tissue may be controlled extrinsically by the cardiac plexuses, and can be stimulated or inhibited by the sympathetic and parasympathetic systems, respectively. Conducting fibers will conduct the impulses initiated by the nodal tissues rapidly throughout the different areas of the heart.

Sinu-atrial (SA) node

• Largest collection of nodal tissue

• Located deep to epicardial layer in the superior portion of the crista terminalis

• Supplied by the sinu-atrial nodal br.

• Initiates impulses that spread to both atria

Atrioventricular (AV) node

• Located in interatrial septum near the coronary sinus opening

• Supplied by the AV nodal br.

• Sends signals to the AV bundle (of His), which splits into the right and left bundles around the interventricular septum

  • The bundles will branch into Purkinje fibers which conduct impulses through the ventricular walls (myocardium) and papillary mm.

13. Locate and explain the relevant anatomical relationships and clinical significance of the linked anatomical structures