Exercise 21 Review Sheet Gross Anatomy Of The Heart

Exercise 21 Review Sheet Gross Anatomy of the Heart

The human heart is a muscular organ that drives the circulatory system by pumping blood throughout the body. Understanding its gross anatomy is essential for students of anatomy, physiology, and health‑related fields because it forms the foundation for grasping how the heart functions, how diseases affect it, and how clinical interventions are performed. Exercise 21 in many laboratory manuals focuses on identifying the heart’s external and internal structures, tracing the flow of blood, and recognizing the coronary vessels that supply the myocardium. This review sheet consolidates the key points you need to master for the exercise, providing clear explanations, labeled diagrams (described in text), and study strategies to reinforce retention.

Overview of Heart Anatomy

The heart sits in the middle mediastinum, slightly left of the midline, and is enclosed within a double‑walled sac called the pericardium. The outer fibrous pericardium anchors the heart to surrounding structures, while the inner serous pericardium (parietal and visceral layers) secretes a small amount of fluid that reduces friction during cardiac contractions.

Externally, the heart exhibits four visible surfaces: the base (posterior), apex (inferior left), sternocostal (anterior), and diaphragmatic (inferior) surfaces. Key landmarks include the auricles (ear‑shaped extensions of the atria), the coronary sulcus (also called the atrioventricular groove), and the anterior and posterior interventricular sulci, which house major coronary vessels.

Internally, the heart is divided into four chambers—two atria and two ventricles—separated by a fibrous skeleton that provides structural support and electrical insulation. Valves located at the atrioventricular (AV) openings and the ventricular outlets ensure unidirectional blood flow.

Chambers of the Heart

Important points to remember:

• The left ventricle’s wall is roughly three times thicker than the right ventricle’s because it must generate higher pressure to overcome systemic vascular resistance.
• The interventricular septum separates the left and right ventricles; its muscular portion is thick, while the membranous portion is thin and lies near the aortic valve.
• The fossa ovalis in the right atrial septum marks the fetal foramen ovale; a probe can be passed through it in a fetal heart but not in an adult.

Valves of the Heart

Valves prevent backflow and are classified as atrioventricular (AV) or semilunar valves.

Atrioventricular Valves

1. Tricuspid Valve – located between the right atrium and right ventricle; consists of three leaflets (anterior, posterior, septal) attached to chordae tendineae that arise from the anterior and posterior papillary muscles.
2. Mitral (Bicuspid) Valve – located between the left atrium and left ventricle; has two leaflets (anteromedial and posterolateral) also secured by chordae tendineae from two papillary muscles.

Key concept: During ventricular systole, increased ventricular pressure pushes the AV valve leaflets toward the atria; the chordae tendineae prevent prolapse into the atrial cavity.

Semilunar Valves

1. Pulmonary Valve – guards the opening from the right ventricle to the pulmonary trunk; three crescent-shaped leaflets (left, right, anterior).
2. Aortic Valve – guards the opening from the left ventricle to the aorta; three leaflets (left coronary, right coronary, non‑corresponding).

Key concept: Semilunar valves open when ventricular pressure exceeds arterial pressure during systole and close when arterial pressure exceeds ventricular pressure during diastole, producing the second heart sound (S2).

Major Blood Vessels Associated with the Heart

Veins Returning Blood to the Heart

• Superior Vena Cava (SVC) – drains blood from the head, neck, upper limbs, and thoracic wall into the right atrium.
• Inferior Vena Cava (IVC) – drains blood from the abdomen, pelvis, and lower limbs into the right atrium (just above the coronary sinus opening).
• Coronary Sinus – collects venous blood from the myocardium and empties into the right atrium between the IVC opening and the tricuspid valve; its tributaries include the great, middle, and small cardiac veins.

Arteries Delivering Blood from the Heart

• Pulmonary Trunk – arises from the right ventricle, bifurcates into left and right pulmonary arteries that carry deoxygenated blood to the lungs.
• Aorta – the largest artery; originates from the left ventricle, ascends (ascending aorta), arches over the pulmonary trunk (aortic arch), then descends (descending thoracic and abdominal aorta). Branches of the ascending aorta supply the coronary arteries.

Coronary Circulation (the heart’s own blood supply) - Right Coronary Artery (RCA) – originates from the right aortic sinus, runs in the right atrioventricular (coronary) sulcus, gives off the right marginal artery and usually the posterior descending artery (PDA) (in a right‑dominant system). Supplies the right atrium, right ventricle, inferior left ventricle, and posterior septum. - Left Coronary Artery (LCA) – originates from the left aortic sinus, quickly bifurcates into the left anterior descending artery (LAD) (also called the anterior interventricular artery) and the circumflex artery (LCx). The LAD runs in the anterior interventricular sulcus; the LCx follows the left atrioventricular sulcus and may give rise to the left marginal artery and, in a left‑dominant system, the PDA.

Coronary Venous Drainage

Complementing the arterial supply, the heart's venous drainage primarily occurs through the coronary sinus, as previously mentioned. However, a significant volume of deoxygenated blood from the myocardial capillary beds also drains directly into the right atrium via smaller anterior cardiac veins and the smallest cardiac veins (Thebesian veins), which open directly into all four cardiac chambers.

Cardiac Conduction System

The coordinated contraction of the heart is governed by its intrinsic electrical conduction system, a specialized network of myocardial cells.

• Sinoatrial (SA) Node: Located in the superior wall of the right atrium near the opening of the superior vena cava, it is the primary pacemaker, initiating each heartbeat.
• Atrioventricular (AV) Node: Situated in the interatrial septum near the tricuspid valve, it introduces a critical delay, allowing atrial contraction to complete and ventricles to fill before ventricular depolarization begins.
• Bundle of His (AV Bundle): Penetrates the fibrous skeleton from the AV node, traveling within the interventricular septum.
• Right and Left Bundle Branches: Descend from the Bundle of His along either side of the interventricular septum, with the left branch further dividing into anterior and posterior fascicles.
• Purkinje Fibers: The terminal branches that rapidly distribute the depolarization impulse through the ventricular myocardium, ensuring a coordinated, near-simultaneous contraction from the apex upward.

Conclusion

The heart's extraordinary function as a relentless pump is a direct consequence of its elegant and integrated anatomical design. The unidirectional valves—atrioventricular and semilunar—ensure efficient blood flow, while the precise timing of their operation is governed by the coordinated pressure changes within the cardiac chambers. This mechanical efficiency is supported by the dedicated coronary circulation, which supplies the myocardium itself via the right and left coronary arteries and their intricate branches. Finally, the intrinsic conduction system provides the precise electrical command, translating neural and hormonal inputs into the synchronized rhythmic contraction that sustains circulation. Together, these components—valves, vessels, and conduction pathways—form a unified, dynamic organ perfectly adapted to its role as the central engine of the cardiovascular system.