The Heart

THE CARDIOVASCULAR SYSTEM: THE HEART

ANATOMY OF THE HEART

  • Key Structures:

    • Right ventricle

    • Pulmonary trunk

    • Pulmonary valve

    • Left coronary artery

    • Left ventricle

    • Bicuspid (Mitral) valve

    • Aortic valve

    • Right coronary artery

    • Ascending aorta

  • View Orientation:

    • Anterior and posterior aspects

    • Superior view of atrioventricular and semilunar valves

FUNCTION OF THE HEART

  • Main Functions:

    • Generating Blood Pressure (BP)

    • Routing Blood through the body

    • Ensuring One-way Blood Flow

    • Regulating Blood Supply

  • Circulation Types:

    • Pulmonary Circulation (to the lungs)

    • Carbon Dioxide (CO2) removal

    • Systemic Circulation

    • Circulation to tissues of head, neck, and upper limbs

    • Circulation to tissues of thorax, abdomen, and lower limbs

HEART LOCATION

  • Location:

    • In the mediastinum between the sternum and vertebral column, between lungs.

    • Starts from around rib 2, apex of the heart rests on the diaphragm (left side).

HEART ORIENTATION

  • Orientation Details:

    • Apex: Directed anteriorly, inferiorly, and to the left, rests on the diaphragm.

    • Base: Directed posteriorly, superiorly, and to the right.

    • Anterior Surface: Deep to the sternum and ribs.

    • Inferior Surface: Rests on the diaphragm.

    • Right Border: Faces the right lung.

    • Left Border: Faces the left lung (pulmonary border).

LAYERS OF HEART WALL

  • Layers Explained:

    • Epicardium:

    • Serous pericardium composed of a parietal layer and a visceral layer.

    • The pericardial cavity is located between these layers, filled with pericardial fluid that reduces friction.

    • Myocardium:

    • Middle layer, composed of cardiac muscle, facilitates heart contractions.

    • Endocardium:

    • Lines the heart chambers and valves, made of simple squamous tissue for smooth blood flow.

    • Fibrous Pericardium:

    • Made of dense irregular tissue, anchors the heart, prevents overfilling, and protects internal structures.

MUSCLE BUNDLES OF THE MYOCARDIUM

  • Key Components:

    • Superior vena cava

    • Aorta

    • Right pulmonary artery branches

    • Right atrium

    • Right ventricle

    • Coronary sulcus

    • Anterior interventricular artery

    • Left ventricle

    • Inferior vena cava

EXTERNAL COMPONENTS OF THE HEART

  • Important Structures:

    • Auricles: Left and right, aid in increasing the capacity of the atria.

    • Superior Vena Cava: Carries deoxygenated blood from head, neck, and upper limbs to the right atrium.

    • Inferior Vena Cava: Carries deoxygenated blood from the lower body to the right atrium.

    • Pulmonary Trunk: Passageway for blood from the right ventricle.

    • Pulmonary Veins: Carry oxygenated blood from lungs to left atrium.

    • Pulmonary Arteries: Only arteries that carry deoxygenated blood to the lungs.

    • Aorta: Main artery conveying blood away from the heart.

CHAMBERS AND SULCI OF THE HEART

  • Chambers:

    • Four chambers total: 2 upper atria and 2 lower ventricles.

  • Sulci:

    • Grooves on the heart's surface that contain coronary vessels and fat:

    • Coronary sulcus: Encircles the heart, marking the boundary between atria and ventricles.

    • Anterior interventricular sulcus: Marks the anterior boundary between ventricles.

    • Posterior interventricular sulcus: Marks the posterior boundary between ventricles.

RIGHT ATRIUM

  • Function: Receives blood from three sources:

    • Superior vena cava

    • Inferior vena cava

    • Coronary sinus

  • Partitioning: Interventricular septum partitions the atria.

RIGHT VENTRICLE

  • Key Features:

    • Papillary Muscles: Tighten chordae tendineae to prevent improper closure of the tricuspid valve.

    • Chordae Tendineae: Cords connecting valve cusps to papillary muscles.

    • Interventricular Septum: Separates the ventricles.

LEFT ATRIUM

  • Function: Receives oxygen-rich blood from lungs via:

    • Pulmonary veins (left and right).

  • Structures: Contains chordae tendineae and papillary muscles connecting to the left ventricle.

LEFT VENTRICLE

  • Function: Receives blood from left atrium, sends blood to the aorta for systemic distribution.

  • Features:

    • Papillary Muscles: Prevent improper closure of the bicuspid valve.

    • Chordae Tendineae: Cords between valve cusps and papillary muscles.

VALVES OF THE HEART

  • Types of Valves:

    • Bicuspid Valve (Mitral Valve): Blood passes to the left ventricle.

    • Tricuspid Valve: Blood flows into the right ventricle, made of dense connective tissue covered by endocardium.

    • Aortic Semilunar Valve: Blood flows into the ascending aorta, distributing to the body; coronary arteries originate above this valve.

    • Pulmonary Semilunar Valve: Allows blood into the pulmonary trunk, directing it to the lungs (CO2 removal).

ATRIOVENTRICULAR VALVES

  • Functionality:

    • AV valves close to prevent backflow into atria during ventricular contraction.

    • Mechanism: Ventricular contraction pushes valve cusps closed; chordae tendineae and papillary muscles prevent cusps from everting.

CIRCULATION OF BLOOD

  • Blood Flow Pathway:

    • Begins at = Superior/Inferior vena cava → Right atrium → Tricuspid valve → Right ventricle → Pulmonary semilunar valve → Pulmonary trunk → Pulmonary arteries → Lungs (gas exchange) → Oxygenated blood returns via pulmonary veins → Left atrium → Bicuspid valve → Left ventricle → Aortic semilunar valve → Aorta → Rest of body.

CORONARY CIRCULATION

  • Definition: Flow of blood through vessels in the myocardium, delivering oxygen and nutrients and removing CO2 and waste.

  • Clinical Note: Blockage in coronary arteries can deprive heart muscle of oxygen, leading to potential reperfusion damage.

CORONARY ARTERIES

  • Branches from: Aorta above aortic semilunar valve:

    • Left Coronary Artery:

    • Circumflex branch: Supplies left atrium and left ventricle.

    • Anterior interventricular artery: Supplies both ventricles and interventricular septum.

    • Right Coronary Artery:

    • Marginal branch: Supplies right atrium, right ventricle, and myocardium.

    • Posterior interventricular artery: Supplies both ventricles posteriorly.

CORONARY VEINS

  • Function: Collect waste from cardiac muscle.

  • Drain into the coronary sinus on the heart's posterior surface, which empties into the right atrium.

AUTORHYTHMIC CELLS AND CONDUCTION SYSTEM

  • Definition: Cardiac muscle cells that are self-excitable, generating spontaneous action potentials triggering heart contractions.

  • PACEMAKER: Sinoatrial (SA) node sets heart rhythm.

  • Components of the Conduction System:

    • Sinoatrial (SA) Node

    • Atrioventricular (AV) Node

    • Atrioventricular Bundle (Bundle of His)

    • Right and Left Bundle Branches

    • Purkinje Fibers

PHYSIOLOGY: CONDUCTION OF THE HEART

  • Process:

    1. Signal generated in the SA node travels throughout the right atrium to the left atrium, leading to atrial contraction (depolarization).

    2. Signal reaches the AV node for processing.

    3. Travels down to the AV bundle to the bundle branches in the interventricular septum leading to ventricular contraction.

    4. Purkinje fibers distribute the signal to the ventricular muscle, leading to their contraction in sequence from apex to base.

ELECTROCARDIOGRAM

  • Definition: A recording of the electrical changes accompanying each cardiac cycle (heartbeat).

  • Purpose: To assess if conduction pathways are abnormal, and to check for heart enlargement or damage.

  • Waveforms:

    • P wave: Atrial depolarization (contraction)

    • QRS complex: Ventricular depolarization (contraction)

    • T wave: Ventricular repolarization (relaxation)

AUSCULTATION

  • Definition: Act of listening to internal sounds using a stethoscope.

  • Heartbeat Sounds:

    • First heart sound (lubb): Caused by turbulence from the closure of atrioventricular valves after ventricular systole begins.

    • Second heart sound (dupp): Represents closure of semilunar valves toward the end of ventricular systole.

REGULATION OF HEART RATE

  • Control Mechanisms:

    • Nervous regulation from the cardiovascular center in the medulla oblongata.

    • Sympathetic impulses increase heart rate; parasympathetic impulses decrease heart rate.

    • Baroreceptors (pressure receptors) detect changes in BP and signal to the cardiovascular center.

    • Factors influencing heart rate include hormones (e.g., epinephrine, norepinephrine, thyroid hormones), ions (Na+, K+, Ca2+), and individual factors (age, gender, physical fitness, temperature).

CLINICAL PROBLEMS

  • Coronary Artery Disease (CAD):

    • Condition of inadequate blood supply to heart muscle due to vessel obstruction.

    • Leading cause of death in the U.S.

    • Causes include atherosclerosis (arterial hardening), artery spasms, clots in coronary arteries.

    • Risk Factors: High cholesterol, hypertension, smoking, obesity, diabetes, high-stress personality types, sedentary lifestyle.

  • Treatment Options: Drugs, bypass grafts, angioplasty, stents.