Anatomy & Physiology: The Cardiovascular System – The Heart (Chapter 17 Part A Study Notes)

Heart Anatomy

The Pulmonary and Systemic Circuits

The heart functions as a dual pump, maintaining two distinct circulatory pathways: the pulmonary and systemic circuits. These circuits ensure the efficient transport of blood, oxygen, and nutrients throughout the body.

• Right Side of the Heart: Receives oxygen-poor blood from body tissues and pumps it to the lungs via the pulmonary circuit to eliminate CO2 and absorb O2.

• Left Side of the Heart: Receives oxygen-rich blood from the lungs and pumps it to body tissues via the systemic circuit.

Receiving and Pumping Chambers

• Right Atrium: Receives blood returning from the systemic circuit.

• Left Atrium: Receives blood returning from the pulmonary circuit.

• Right Ventricle: Pumps blood through the pulmonary circuit.

• Left Ventricle: Pumps blood through the systemic circuit.

Size, Location, and Orientation of the Heart

The heart is a muscular organ approximately the size of a fist and weighs less than 1 pound. Its anatomical position is crucial for its function and protection.

• Location: Situated in the mediastinum between the second rib and fifth intercostal space, on the superior surface of the diaphragm. Two-thirds of the heart lies to the left of the midsternal line, anterior to the vertebral column and posterior to the sternum.

• Base: The posterior surface leans toward the right shoulder.

• Apex: Points toward the left hip; the apical impulse can be palpated between the fifth and sixth ribs, just below the left nipple.

Coverings of the Heart

The heart is enclosed by the pericardium, a double-walled sac that provides protection and reduces friction during heartbeats.

• Fibrous Pericardium: The superficial layer that anchors the heart and prevents overfilling.

• Serous Pericardium: Composed of two layers:

  • Parietal Layer: Lines the internal surface of the fibrous pericardium.

  • Visceral Layer (Epicardium): Covers the external surface of the heart.

• The two layers are separated by the pericardial cavity, filled with fluid to decrease friction.

Clinical Note: Pericarditis and Cardiac Tamponade

• Pericarditis: Inflammation of the pericardium, causing a pericardial friction rub (creaking sound).

• Cardiac Tamponade: Excess fluid in the pericardial space compresses the heart, impairing its pumping ability. Treatment involves fluid removal.

Layers of the Heart Wall

The heart wall consists of three distinct layers, each with specialized functions.

• Epicardium: The visceral layer of the serous pericardium.

• Myocardium: Composed of circular or spiral bundles of contractile cardiac muscle cells.

  • Cardiac Skeleton: A crisscrossing, interlacing layer of connective tissue that anchors muscle fibers, supports vessels and valves, and limits the spread of action potentials.

• Endocardium: The innermost layer, continuous with the endothelial lining of blood vessels, lining heart chambers and covering the cardiac skeleton of valves.

Chambers and Associated Great Vessels

Internal Features

• Four Chambers:

  • Two superior atria (receiving chambers)

  • Two inferior ventricles (discharging chambers)

• Interatrial Septum: Separates the atria; contains the fossa ovalis, a remnant of the fetal foramen ovale.

• Interventricular Septum: Separates the ventricles.

Surface Features

• Coronary Sulcus (Atrioventricular Groove): Encircles the junction of atria and ventricles.

• Anterior Interventricular Sulcus: Marks the anterior position of the interventricular septum.

• Posterior Interventricular Sulcus: Landmark on the posteroinferior surface.

Atria: The Receiving Chambers

• Small, thin-walled chambers with auricles to increase volume.

• Right Atrium: Receives deoxygenated blood from the body via:

  • Superior vena cava (above diaphragm)

  • Inferior vena cava (below diaphragm)

  • Coronary sinus (from coronary veins)

• Left Atrium: Receives oxygenated blood from the lungs via four pulmonary veins.

Ventricles: The Discharging Chambers

• Thicker walls than atria; actual pumps of the heart.

• Right Ventricle: Pumps blood into the pulmonary trunk.

• Left Ventricle: Pumps blood into the aorta (largest artery).

• Trabeculae Carneae: Irregular ridges of muscle on ventricular walls.

• Papillary Muscles: Anchor chordae tendineae attached to heart valves.

Heart Valves

Types and Functions

Heart valves ensure unidirectional blood flow and open/close in response to pressure changes.

• Atrioventricular (AV) Valves: Located between atria and ventricles.

  • Tricuspid Valve: Right AV valve, three cusps.

  • Mitral Valve (Bicuspid): Left AV valve, two cusps.

  • Chordae Tendineae: Anchor valve cusps to papillary muscles, preventing backflow into atria.

• Semilunar (SL) Valves: Located between ventricles and major arteries.

  • Pulmonary Semilunar Valve: Between right ventricle and pulmonary trunk.

  • Aortic Semilunar Valve: Between left ventricle and aorta.

  • Each SL valve has three half-moon-shaped cusps.

• No valves between major veins and atria; backflow is prevented by inertia and compression during heart contraction.

Table: Heart Chambers and Associated Vessels

Chamber	Receives Blood From	Pumps Blood To
Right Atrium	Systemic veins (SVC, IVC, coronary sinus)	Right ventricle
Right Ventricle	Right atrium	Pulmonary trunk (lungs)
Left Atrium	Pulmonary veins (lungs)	Left ventricle
Left Ventricle	Left atrium	Aorta (systemic circulation)

Additional info:

• These notes are based on textbook slides and images, with academic context added for clarity and completeness.