THE HEART ANATOMY 2

Heart Innervation

• Overview: Heart innervation involves the regulation of heart function by both parasympathetic and sympathetic nerve fibers. Parasympathetic fibers, primarily from the vagus nerve, inhibit heart activity, while sympathetic fibers stimulate the heart. Referred pain from the heart is often felt in areas innervated by the same spinal cord levels.

• Parasympathetic Fibers:

  • Origin: Vagus nerve.

  • Function: Inhibit heart rate and contraction strength.

  • Pathway: Cardioinhibitory center in the medulla oblongata.

• Sympathetic Fibers:

  • Origin: Sympathetic trunk ganglion.

  • Function: Stimulate heart rate and contraction strength.

  • Pathway: Cardioacceleratory center in the medulla oblongata, via sympathetic cardiac nerves from the thoracic spinal cord.

• Referred Pain:

  • Definition: Pain originating from the heart is perceived as coming from another location.

  • Mechanism: Brain misinterprets the pain as originating from an area innervated by the same spinal cord level.

  • Location: Visceral pain is referred to the body wall or limb region.

• Dermatome:

  • Heart: Spinal cord levels T1-T4.

  • Pain Referral: Pain from the heart (T1-T4) is often referred to the arm and chest wall.

  • Perception: Diffuse pain is perceived in the T1-T4 dermatome.

Heart Wall Composition

• Overview: The heart wall consists of three layers: the epicardium (outer layer), the myocardium (middle layer), and the endocardium (inner layer). Each layer has a distinct structure and function that contributes to the overall function of the heart.

• Epicardium:

  • Visceral layer of the serous pericardium

  • Composition: Simple squamous epithelium and loose connective tissue with fat.

• Myocardium:

  • Cardiac muscle layer.

  • Thickness varies: ventricles are thicker than atria (V>A), and the left ventricle is thicker than the right ventricle (LV > RV).

• Endocardium:

  • Inner lining of the heart.

  • Features trabeculae carneae.

Heart's Conducting System

• Overview: The heart's conducting system is a specialized network of modified cardiac muscle cells responsible for initiating and coordinating the heart's rhythmic contractions. It ensures efficient and synchronized pumping of blood through the pulmonary and systemic circuits. The main components include the SA node, AV node, Bundle of His, and Purkinje fibers.

• SA Node:

  • Pacemaker of the heart.

  • Located in the wall of the right atrium at the junction of the superior vena cava (SVC).

  • Initiates electrical impulses that trigger atrial contraction.

• AV Node:

  • Located in the interatrial septum.

  • Receives impulses from the SA node.

  • Delays the impulse to allow for complete atrial contraction before ventricular contraction.

• Bundle of His:

  • Located in the interventricular septum.

  • Conducts the impulse from the AV node to the ventricles.

  • Divides into right and left bundle branches.

• Purkinje Fibers:

  • Network of fibers that extend throughout the ventricular myocardium.

  • Rapidly transmit the impulse to the ventricular muscle cells, causing ventricular contraction.

Blood Supply to Heart

• Overview: The heart's blood supply is crucial for its function, involving coronary arteries that deliver oxygenated blood and coronary veins that remove deoxygenated blood. Procedures like coronary catheterization, angioplasty, and stent placement are used to address blockages and improve blood flow to the heart.

• Coronary Arteries:

  • Deliver oxygenated blood to the heart muscle.

  • The right coronary artery has branches such as the sinuatrial (SA) nodal branch and the posterior interventricular branch (posterior descending artery).

  • Dye is injected into the coronary arteries during arteriography for visualization.

• Coronary Veins:

  • Remove deoxygenated blood from the heart muscle.

  • Include the anterior cardiac veins, great cardiac vein, small cardiac vein, and middle cardiac vein.

• Coronary Sinus:

  • A collection of veins joined together to form a large vessel that collects blood from the heart muscle.

  • Drains into the right atrium.

• Coronary Catheterization:

  • Involves threading a catheter up to the aorta to the origin of the coronary arteries.

  • Catheter entrance is typically through the femoral artery.

• Angioplasty:

  • Procedure used to widen partially blocked arteries.

• Stent:

  • A stent with a balloon is inserted into the blocked artery.

  • The balloon is inflated to expand the stent, opening the artery.

  • The balloon is then removed, leaving the expanded stent in place to maintain blood flow.

Heart Valves

• Overview: Heart valves prevent the backflow of blood, ensuring unidirectional flow through the heart. There are two main types: atrioventricular valves, located between the atria and ventricles, and semilunar valves, found at the junction of the ventricles and great arteries. Valve disease can involve stenosis or incompetence.

• Atrioventricular Valves:

  • Located between the atria and ventricles.

  • Right side: Tricuspid valve.

  • Left side: Bicuspid/Mitral valve.

  • Function: During ventricular contraction, papillary muscles contract, holding the chordae tendineae to prevent the valve cusps from being forced back into the atria, thus closing the AV orifice.

• Semilunar Valves:

  • Located at the junction of the ventricles and the great arteries (aorta and pulmonary artery).

  • Function: During ventricular systole (contraction), the cusps are pushed towards the vessel wall by the blood. During ventricular diastole (relaxation), blood is forced back, filling the pocket-shaped cusps and forcing them together, closing the valve orifice.

• Valve Stenosis:

  • The valve does not open properly, resulting in a narrowed opening.

• Valve Incompetence:

  • Also known as regurgitation or insufficiency.

  • The valve does not close properly, leading to backflow of blood.

Heart Coverings

• Overview: The heart is enclosed within a protective sac called the pericardium, which consists of two main layers: the fibrous pericardium and the serous pericardium. The serous pericardium further divides into parietal and visceral layers, with the pericardial cavity in between containing pericardial fluid for friction-free heart movement.

• Fibrous Pericardium:

  • Outer layer made of fibrous connective tissue.

  • Adherent to the central tendon of the diaphragm.

  • Fused with the adventitia of the great vessels.

• Serous Pericardium:

  • Two layers:

    • Parietal pericardium: Lines the inner surface of the fibrous pericardium.

    • Visceral pericardium (Epicardium): Covers the outer surface of the heart.

  • Composed of simple squamous epithelium and loose connective tissue.

• Pericardial Cavity:

  • Space between the parietal and visceral layers of the serous pericardium.

  • Contains pericardial fluid.

• Pericardial Fluid:

  • Located within the pericardial cavity.

  • Provides lubrication for friction-free movement of the heart.

• Pericarditis:

  • Inflammation of the pericardium.

• Pericardial Effusion:

  • Accumulation of excess fluid in the pericardial cavity.

  • Can impair cardiac function.

Heart Chambers

• Overview: The heart has four chambers: the right and left atria, which receive blood, and the right and left ventricles, which pump blood. These chambers are separated by the interatrial and interventricular septa, ensuring no direct communication between the right and left sides of the heart. The heart functions as two pumps in series, driving pulmonary and systemic circulations.

• Right Atrium:

  • Receives deoxygenated blood from the systemic circulation via the superior vena cava (SVC), inferior vena cava (IVC), and coronary sinus.

  • Features the fossa ovalis, a depression in the interatrial septum, which is a remnant of the foramen ovale in the embryo.

• Left Atrium:

  • Receives oxygenated blood from the pulmonary veins.

• Right Ventricle:

  • Pumps deoxygenated blood into the pulmonary arteries for pulmonary circulation.

• Left Ventricle:

  • Pumps oxygenated blood into the aorta for systemic circulation.

  • Heart twisted to the left.

• Interatrial Septum:

  • Separates the right and left atria.

  • Contains the fossa ovalis.

• Interventricular Septum:

  • Separates the right and left ventricles.

  • Has a muscular portion.

• Auricles:

  • Left auricle shown.

Circulation

• Overview: Circulation in the human body involves two main circuits, pulmonary and systemic, driven by the heart's pumping action. The heart is divided into right and left sides, each functioning as a separate pump. Atria receive blood, while ventricles pump blood out.

• Pulmonary Circulation:

  • Carries deoxygenated blood from the right ventricle to the lungs.

  • In the lungs, gas exchange occurs, and blood becomes oxygenated.

  • Oxygenated blood returns to the left atrium via pulmonary veins.

• Systemic Circulation:

  • Carries oxygenated blood from the left ventricle to the body tissues.

  • Blood travels through the aorta and its branches to capillary beds.

  • Gas exchange occurs in the tissues, and deoxygenated blood returns to the right atrium via the superior vena cava (SVC) and inferior vena cava (IVC).

• Atria:

  • Receive blood returning to the heart.

  • Right atrium receives deoxygenated blood from the systemic circulation (SVC & IVC).

  • Left atrium receives oxygenated blood from the pulmonary circulation (pulmonary veins).

• Ventricles:

  • Pumping chambers of the heart.

  • Right ventricle pumps deoxygenated blood to the pulmonary circulation (pulmonary artery).

  • Left ventricle pumps oxygenated blood to the systemic circulation (aorta).