Heart Chambers, Vessels, and Valves

COM 200: Heart Chambers, Vessels, and Valves

Conducting System of the Heart

General Function and Components of the Cardiovascular System (CVS)

  • Cardiovascular System Definition:

    • The cardiovascular system consists of the heart and blood vessels.

  • Main Functions:

    • Transports blood throughout the body.

    • Responsible for:

    • Delivery of oxygen (O2) and nutrients.

    • Removal of carbon dioxide (CO2) and wastes.

  • Blood Vessels Overview:

    • Arteries:

    • Carry blood away from the heart.

    • Most arteries carry oxygenated blood (exception: pulmonary arteries).

    • Veins:

    • Carry blood back to the heart.

    • Most veins carry deoxygenated blood (exception: pulmonary veins).

    • Capillaries:

    • Sites of exchange of gases and nutrients between blood and body cells, as well as between blood and air in lungs.

Two Sides of the Heart

  • Right Side of the Heart:

    • Receives deoxygenated blood and pumps it to the lungs.

  • Left Side of the Heart:

    • Receives oxygenated blood and pumps it to the body.

  • Chambers:

    • Atria: Superior chambers that receive blood and send it to ventricles.

    • Ventricles: Inferior chambers that pump blood away from the heart.

The Great Vessels

  • Functions:

    • Transport blood to and from the heart's chambers.

  • Key Vessels:

    • Superior Vena Cava and Inferior Vena Cava: Drain deoxygenated blood into the right atrium.

    • Pulmonary Trunk: Transports blood from the right ventricle and splits into pulmonary arteries.

    • Pulmonary Veins: Drain oxygenated blood into the left atrium.

    • Aorta: Transports blood from the left ventricle.

Heart Valves

  • Purpose:

    • Ensure one-way flow of blood through the heart.

  • Types of Valves:

    • Atrioventricular (AV) Valves: Located between the atrium and ventricle of each side.

    • Right AV Valve (Tricuspid):

    • Left AV Valve (Bicuspid or Mitral):

    • Semilunar Valves: Located at the boundary of the ventricle and arterial trunk.

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

    • Aortic Semilunar Valve: Between left ventricle and aorta.

Pulmonary and Systemic Circulation

  • Pulmonary Circulation:

    • Carries deoxygenated blood from the right side of the heart to the lungs.

    • Blood picks up oxygen and releases carbon dioxide at the lungs.

    • Returns oxygenated blood to the left side of the heart.

  • Systemic Circulation:

    • Carries oxygenated blood from the left side of the heart to systemic cells (skin, muscles).

    • Exchanges gases, nutrients, and wastes at systemic cells.

    • Returns deoxygenated blood to the right side of the heart.

  • Basic Pattern: Right heart → lungs → left heart → systemic tissues → right heart.

Heart Position Within the Thoracic Cavity

  • The heart is located within the thoracic cavity, which is supported by the thoracic cage.

  • Conventional Placement:

    • Sits posterior to the sternum and left of the body midline.

    • Found between the lungs in the mediastinum.

    • Slightly rotated: right side positioned more anteriorly than left side.

  • Anatomical Landmarks:

    • Base: Postero-superior surface of the heart.

    • Apex: Inferior, conical end that projects slightly anteroinferiorly toward the left side of the body.

External Anatomy of the Heart: Anterior View

  • Key Structures:

    • Right Ventricle

    • Right Atrium

    • Right Auricle

    • Left Ventricle

    • Left Auricle

    • Aorta

    • Pulmonary Trunk

    • Superior Vena Cava

    • Inferior Vena Cava

    • Anterior Interventricular Sulcus:

    • Groove containing coronary vessels supplying blood to the heart wall.

External Anatomy of the Heart: Posterior View

  • Key Structures:

    • Left Atrium

    • Left Ventricle

    • Pulmonary Veins

    • Superior Vena Cava

    • Inferior Vena Cava

    • Pulmonary Arteries

    • (from pulmonary trunk).

    • Aorta

    • Coronary Sulcus

    • Posterior Interventricular Sulcus: Groove located at the back of the heart.

Layers of the Heart Wall

  • Epicardium:

    • The outermost heart layer.

    • Also known as the serous layer of the visceral pericardium.

  • Myocardium:

    • The middle layer of the heart wall and the thickest.

    • Composed of cardiac muscle tissue, contracts to pump blood.

  • Endocardium:

    • Covers the internal surface of the heart and external surface of the valves.

Septa of the Heart

  • Interatrial Septum: Separates the left atrium from the right atrium.

    • Fossa Ovalis: Oval depression on the interatrial septum, occupying the location of fetal foramen ovale, which shunted blood from right to left atrium during fetal life.

  • Interventricular Septum: Separates the left ventricle from the right ventricle.

Heart Valves: Locations

  • Atrioventricular Valves:

    1. Right AV Valve (Tricuspid):

    • Located between the right atrium and ventricle; has three flaps.

    1. Left AV (Mitral) Valve:

    • Located between the left atrium and ventricle; has two flaps.

  • Semilunar Valves:

    1. Pulmonary Semilunar Valve: Between the right ventricle and the pulmonary trunk.

    2. Aortic Semilunar Valve: Between the left ventricle and the aorta.

Clinical View: Heart Sounds and Heart Murmurs

  • Valvular Insufficiency:

    • Cardiac valves leak because their cusps do not close tightly, resulting in blood regurgitating back through the valve.

    • May lead to heart enlargement over time.

  • Valvular Stenosis:

    • Valve cusps become scarred and cannot open completely, presenting resistance to blood flow, which reduces chamber output.

    • Primary cause is often rheumatic heart disease.

Blood Supply Within the Heart Wall: Coronary Arteries

  • Right Coronary Artery and Left Coronary Artery:

    • These sit in the coronary sulcus and branch off from the ascending aorta.

    • Transport oxygenated blood to the heart wall.

  • Arterial Anastomoses:

    • Connections between vessels that allow blood to arrive via more than one route, providing redundancy in blood supply.

Cardiac Veins

  • Types of Cardiac Veins:

    • Middle Cardiac Vein

    • Small Cardiac Vein

    • Coronary Sinus

    • Great Cardiac Vein

  • These veins transport deoxygenated blood away from the heart wall toward the right atrium.

Clinical View: Coronary Heart Disease, Angina Pectoris, and Myocardial Infarction

  • Coronary Heart Disease:

    • Characterized by the buildup of plaque in coronary arteries (atherosclerosis), which reduces blood flow to heart muscle.

  • Coronary Spasm:

    • Sudden narrowing of the vessels which can lead to angina or myocardial infarction.

    • Angina Pectoris:

    • Characterized by heart pain during strenuous activity, usually felt on the left side of the chest, left arm, or jaw.

    • Treatments often aim to induce vascular dilation.

    • Myocardial Infarction (Heart Attack):

    • Results from sudden and complete occlusion of a coronary artery, depriving myocardium of oxygen.

    • Symptoms include excruciating chest pain radiating down the left arm, weakness, shortness of breath, nausea, anxiety, and sweating.

Conduction System of the Heart

  • Definition:

    • The conduction system initiates and propagates an action potential, which leads to cardiac muscle contraction.

    • This contraction process occurs first in the atria and then in the ventricles.

Initiation and Spread of the Action Potential

  • Sinoatrial (SA) Node:

    • The site where contraction of heart muscle is initiated. Known as the pacemaker of the heart, it is situated in the upper part of the right atrium.

  • Atrioventricular (AV) Node:

    • Receives impulses from the SA node and is situated in the lower part of the atrial septum.

  • Atrioventricular (AV) Bundle of His:

    • Descends from the AV node to the membranous portion of the ventricular septum.

    • Divides into the left and right bundle branches that extend to the myocardium of the right and left ventricles.

  • Purkinje Fibers:

    • Subendocardial branches that conduct the action potential through the ventricles, leading to contraction.

Innervation of the Heart

  • Cardiac Center:

    • Located within the medulla oblongata of the brain.

    • Receives signals from baroreceptors and chemoreceptors in the cardiovascular system.

  • Function:

    • Sends signals via sympathetically innervated pathways (from T1–T5 segments of the spinal cord) and parasympathetic pathways (vagus nerves (CN X)).

    • Modifies (does not initiate) cardiac activity, influencing the rate and force of the heart's contractions.

Clinical View: Ectopic Pacemaker

  • Ectopic Pacemaker Definition:

    • A pacemaker other than the SA node.

    • The AV node can function as the default pacemaker if the SA node is impaired, with an inherent rhythm of 40 to 50 beats per minute, sufficient to sustain life.

    • If cardiac muscle is the default pacemaker, it typically operates at 20 to 40 beats per minute, which is usually too slow to sustain life.

  • Mechanical Pacemaker:

    • A device that can be implanted to sustain a sufficient heart rate for patients with dysfunctional pacemakers.

  • Bradycardia:

    • Defined as persistently low resting heart rate in adults (below 60 beats/minute), typically normal in athletes, but is also a potential sign of health issues like hypothyroidism, electrolyte imbalance, and congestive heart failure.

  • Tachycardia:

    • Defined as persistently high resting heart rate (over 100 beats/minute). Common causes include heart disease, fever, and anxiety.