Anatomy of the Heart

Anatomy of the Heart Notes

Objectives

• Describe the heart's location.

• Name the three layers and covering of the heart.

• Explain its function as two separate pumps.

• Identify the four chambers and great vessels.

• Explain the function of the heart valves.

• Describe the physiological basis of heart sounds.

• Describe blood flow through the heart.

• List vessels supplying blood to the heart.

• Identify the heart's conduction system components.

Key Terms

• Aortic valve - Valve located at the exit of the left ventricle into the aorta.

• Atrial conducting fibers - Pathways that help transmit electrical impulses through the atria.

• Atrioventricular (AV) valves - Valves between atria and ventricles.

• Endocardium - The innermost layer of the heart.

• Myocardium - The muscular middle layer of the heart responsible for contraction.

• Pericardium - The fibrous sac surrounding the heart.

Function, Location, and Size of the Heart

• Description: The heart is a hollow muscular organ functioning primarily as a pump for blood.

• Location: Found in the thoracic cavity (lower mediastinum) between the lungs, behind the sternum.

  • Size: Approximately the size of a closed fist, weighs less than 1 lb. Two-thirds of it lies to the left of the sternum.

  • Orientation: Base at the level of the second rib; apex at the fifth intercostal space.

Layers and Covering of the Heart

• Endocardium: Innermost layer lining the heart’s chambers and valves.

• Myocardium: Thick middle layer composed of cardiac muscle,

• Epicardium: Thin outer layer that also forms part of the pericardium.

• Pericardium: Sling-like structure supporting the heart, consists of:

  • Visceral pericardium - Inner layer.

  • Parietal pericardium - Outer layer.

  • Fibrous pericardium - Anchors the heart to surrounding structures.

  • Pericardial cavity - Contains lubricating serous fluid (10-30 mL) to reduce friction.

  • Conditions:

  • Pericarditis: Inflammation of pericardial membranes causing pain and friction rub.

  • Cardiac Tamponade: Excess fluid accumulation in the cavity compresses the heart.

A Double Pump and Two Circulations

• Right Heart: Pumps unoxygenated blood through the pulmonary circulation to the lungs for oxygenation.

• Left Heart: Pumps oxygenated blood through systemic circulation to the body.

  • This dual pump functions in synchrony to ensure efficient circulation of blood.

Heart's Chambers and Great Vessels

• Chambers:

  • Atria: Upper chambers receiving blood (right atrium receives unoxygenated blood, left atrium receives oxygenated blood).

  • Ventricles: Lower chambers pumping blood (right ventricle sends blood to lungs, left ventricle pumps into systemic circulation).

  • Septum: Divides right and left heart into two sides (interatrial and interventricular).

• Great Vessels:

  • Venae Cavae: Major veins returning blood to the right atrium.

  • Pulmonary Trunk: Carries blood from right ventricle to lungs.

  • Pulmonary Veins: Return oxygenated blood to the left atrium.

  • Aorta: The largest artery that distributes blood from the left ventricle to the body.

Heart Valves

• Function: Prevent backward blood flow, ensuring unidirectional flow.

• Types:

  • Atrioventricular (AV) valves: Tricuspid (right) and Bicuspid/Mitral (left).

  • Chordae tendineae: Connect valves to papillary muscles, preventing valve inversion during ventricular contraction.

  • Semilunar valves: Pulmonic (right) and Aortic (left);

• Closure Mechanism: Valve closure is pressure-dependent during contraction and relaxation phases.

Heart Sounds

• Heart sounds (C4lubb-duppE) caused by valve closure:

  • S1 (“lubb”): Closure of AV valves at onset of ventricular contraction.

  • S2 (“dupp”): Closure of semilunar valves at onset of ventricular relaxation.

• Abnormal Sounds: Murmurs signify valve malfunction or structural issues.

Pathway of Blood Flow Through the Heart

1. Right Atrium: Receives blood from superior/inferior venae cavae.

2. Right Ventricle: Pumps blood into pulmonary trunk through pulmonic valve.

3. Lungs: Oxygenation occurs in the pulmonary capillaries.

4. Left Atrium: Receives oxygenated blood from pulmonary veins.

5. Left Ventricle: Pumps blood into aorta through aortic valve for distribution to the body.

Blood Supply to the Myocardium

• Coronary Arteries:

  • Right Coronary Artery: Supplies right heart and part of conduction system.

  • Left Coronary Artery: Branches into Left Anterior Descending (LAD) and Circumflex arteries supplying the left heart.

• Coronary Veins: Drain unoxygenated blood into coronary sinus, which empties into the right atrium.

Cardiac Conduction System

• Components: SA Node (pacemaker), AV Node, His-Purkinje System.

  • SA Node: Generates electrical impulses setting heart rate (60-100 bpm).

  • AV Node: Delays impulse transmission to allow ventricle filling.

  • His-Purkinje system: Quickly spreads the impulse throughout the ventricles for coordinated contraction.

Electrocardiogram (ECG)

• Records electrical activity of the heart with key components:

  • P Wave: Atrial depolarization.

  • QRS Complex: Ventricular depolarization.

  • T Wave: Ventricular repolarization.

• Clinical Use: Assess heart's rhythm and detect abnormalities.

Objectives

• Describe the heart's location within the thoracic cavity and the structures surrounding it.

• Name the three layers of the heart wall (endocardium, myocardium, epicardium) and their functions, as well as the covering of the heart (pericardium).

• Explain the function of the heart as two separate pumps for pulmonary and systemic circulation.

• Identify the four chambers of the heart (two atria and two ventricles) and the great vessels connecting to the heart.

• Explain the function of the heart valves (atrioventricular and semilunar valves) in maintaining unidirectional blood flow.

• Describe the physiological basis of normal heart sounds (S1 and S2) and how they correlate with cardiac cycles.

• Describe the pathway of blood flow through the heart in detail, emphasizing oxygenation and nutrient transport.

• List vessels supplying blood to the heart, including coronary arteries and veins, and their specific areas of supply.

• Identify the heart's conduction system components (SA node, AV node, His-Purkinje system) and their roles in the electrical activity of the heart.

Key Terms

• Aortic valve - The valve located at the exit of the left ventricle into the aorta, responsible for ensuring that blood flows in the right direction from the heart to the body.

• Atrial conducting fibers - Specialized pathways that help rapidly transmit electrical impulses through the atria, facilitating efficient atrial contraction.

• Atrioventricular (AV) valves - Valves situated between the atria and ventricles (tricuspid on the right side and mitral on the left) that prevent backflow of blood during ventricular contraction.

• Endocardium - The innermost layer of the heart, made of endothelial cells, which provides a smooth lining for the chambers and valves.

• Myocardium - The thick muscular middle layer of the heart responsible for the contraction that pumps blood.

• Pericardium - The fibrous sac surrounding the heart, providing protection and containing lubricating serous fluid to reduce friction during heartbeats.

Function, Location, and Size of the Heart

• Description: The heart is a hollow muscular organ functioning primarily as a pump for blood circulation throughout the body.

• Location: Found in the thoracic cavity (lower mediastinum) between the lungs, behind the sternum, and tilted slightly to the left.

• Size: Approximately the size of a clenched fist, weighing less than 1 lb (about 250-350 grams). Approximately two-thirds of the heart lies to the left of the midline (sternum).

  • Orientation: The base of the heart is at the level of the second rib; the apex is located at the fifth intercostal space, around the midclavicular line.

Layers and Covering of the Heart

• Endocardium: The innermost layer lining the chambers and valves, provides a smooth surface to minimize turbulence as blood flows through the heart.

• Myocardium: A thick, muscular layer composed of specialized cardiac muscle cells; responsible for the force generation necessary for pumping blood.

• Epicardium: A thin outer layer that also constitutes the inner layer of the pericardium, containing blood vessels and nerves supplying the myocardium.

• Pericardium: A double-walled sac that encases the heart and consists of:

  • Visceral pericardium - The inner layer that is in direct contact with the heart.

  • Parietal pericardium - The outer layer that forms a protective enclosure.

  • Fibrous pericardium - The strong outermost layer anchoring the heart to surrounding structures such as the diaphragm and sternum.

  • Pericardial cavity - Contains 10-30 mL of lubricating serous fluid that reduces friction between the layers during the heart's movement.

  • Conditions:

    • Pericarditis: An inflammation of the pericardial membranes causing localized chest pain and a characteristic friction rub sound during auscultation.

    • Cardiac Tamponade: A condition characterized by excessive accumulation of fluid in the pericardial cavity, which can restrict heart function and necessitate medical intervention.

A Double Pump and Two Circulations

• Right Heart: Pumps unoxygenated blood through the pulmonary circulation, delivering it to the lungs where carbon dioxide is exchanged for oxygen.

• Left Heart: Pumps oxygenated blood through the systemic circulation to supply the body's tissues with oxygen and nutrients.

• This dual pumping mechanism works in synchrony to ensure efficient circulation of blood, maintaining homeostasis in the body.

Heart's Chambers and Great Vessels

• Chambers:

  • Atria: The two upper chambers; the right atrium receives unoxygenated blood from the body via the superior and inferior venae cavae, while the left atrium receives oxygenated blood from the lungs via the pulmonary veins.

  • Ventricles: The two lower chambers; the right ventricle pumps blood into the pulmonary trunk leading to the lungs, while the left ventricle pumps blood into the aorta for systemic distribution.

  • Septum: A muscular wall that divides the right and left heart, consisting of the interatrial septum (separates the atria) and interventricular septum (separates the ventricles).

• Great Vessels:

  • Venae Cavae: Composed of the superior vena cava (returning blood from the upper body) and inferior vena cava (returning blood from the lower body), both draining into the right atrium.

  • Pulmonary Trunk: A major vessel carrying deoxygenated blood from the right ventricle to the lungs for oxygenation.

  • Pulmonary Veins: Four vessels (two from each lung) that return oxygenated blood to the left atrium.

  • Aorta: The largest artery in the body that delivers oxygenated blood from the left ventricle to the systemic circulation, branching into various arteries for organ perfusion.

Heart Valves

• Function: Prevent backward blood flow, ensuring unidirectional flow during the cardiac cycle and maintaining efficient circulation.

• Types:

  • Atrioventricular (AV) valves: Include the tricuspid valve (right) and the mitral valve (bicuspid, left).

  • Chordae tendineae: Fibrous cords connecting the valve leaflets to the papillary muscles, preventing valve inversion during ventricular contraction and maintaining valve function.

  • Semilunar valves: Include the pulmonic valve (right) and the aortic valve (left), responsible for preventing backflow during ventricular diastole.

• Closure Mechanism: The closure of the valves is pressure-dependent and occurs during the contraction and relaxation phases of the heartbeat, contributing to the characteristic heart sounds.

Heart Sounds

• Heart sounds are produced by the closure of the valves and can be auscultated as:

  • S1 (“lubb”): This sound is associated with the closure of the AV valves at the onset of ventricular contraction (systole).

  • S2 (“dupp”): This sound occurs with the closure of the semilunar valves at the onset of ventricular relaxation (diastole).

• Abnormal Sounds: Heart murmurs can indicate valve malfunctions, stenosis, or other structural heart issues and warrant further investigation by a healthcare professional.

Pathway of Blood Flow Through the Heart

1. Right Atrium: Blood from the superior/inferior venae cavae enters the right atrium.

2. Right Ventricle: Blood flows from the right atrium through the tricuspid valve into the right ventricle, which pumps it into the pulmonary trunk through the pulmonic valve.

3. Lungs: In the pulmonary capillaries, blood undergoes oxygenation by exchanging carbon dioxide for oxygen.

4. Left Atrium: Oxygenated blood returns through the pulmonary veins into the left atrium.

5. Left Ventricle: Blood flows from the left atrium through the mitral valve into the left ventricle, which pumps it into the aorta through the aortic valve for distribution to the body.

Blood Supply to the Myocardium

• Coronary Arteries:

  • Right Coronary Artery (RCA): Supplies blood to the right atrium, right ventricle, and parts of the conduction system, such as the SA node in most individuals.

  • Left Coronary Artery (LCA): Branches into the Left Anterior Descending (LAD) artery, which supplies the anterior wall of the left ventricle, and the Circumflex artery that supplies the lateral wall.

• Coronary Veins: Drain deoxygenated blood from the myocardium into the coronary sinus, which empties into the right atrium, thereby completing the heart's circulatory loop.

Cardiac Conduction System

• Components: Includes the Sinoatrial (SA) Node, Atrioventricular (AV) Node, and the His-Purkinje System, which coordinate heart rate and rhythm.

  • SA Node: The primary pacemaker that generates electrical impulses at a rate of 60-100 beats per minute, prompting atrial contraction.

  • AV Node: Positioned at the junction of the atria and ventricles, it provides a critical delay in impulse transmission, allowing sufficient time for ventricular filling before they contract.

  • His-Purkinje System: Rapidly conducts electrical impulses to the ventricular myocardium, resulting in coordinated ventricular contraction necessary for efficient pumping.

Electrocardiogram (ECG)

• Function: The ECG records the electrical activity of the heart and is vital for diagnosing various cardiac conditions.

  • P Wave: Represents atrial depolarization, initiating atrial contraction.

  • QRS Complex: Indicates ventricular depolarization, associated with the contraction of ventricles.

  • T Wave: Reflects ventricular repolarization, during which the ventricles recover electrically after contraction.

• Clinical Use: The ECG is used to assess the heart's rhythm, identify arrhythmias, and detect abnormalities in heart structure and function, providing invaluable information in cardiac care.