Chapter 20

Chapter 20: Cardiovascular System - The Heart

1. Introduction

  • Authors: Elizabeth J. Johnican, Cinnamon VanPutte, Jennifer Regan, Andrew Russo.

  • Edition: Thirteenth Edition, McGraw Hill.

2. Anatomy of the Heart

A. General Structure

  • The heart is a four-chambered muscular organ.

  • Function: Pumps blood through the blood vessels.

  • Surrounded by the pericardium, anchoring it in the mediastinum.

  • Composed of three layers:

    • Epicardium (outer layer), Myocardium (middle layer - cardiac muscle), and Endocardium (inner layer).

3. Functions of the Heart

  • Right side: Pumps blood via pulmonary circulation to the lungs.

  • Left side: Pumps blood through systemic circulation to body tissues.

  • Functions include:

    • Generating blood pressure with contractions.

    • Routing blood effectively between pulmonary and systemic circuits.

    • Ensuring unidirectional blood flow aided by valves.

    • Adjusting heart rate and contraction force based on metabolic needs.

4. Circulation Overview

A. Pulmonary vs. Systemic Circulation

  • Pulmonary circulation: Right side to lungs.

  • Systemic circulation: Left side to body tissues.

5. Size, Shape, and Location

  • Size: Approximately the size of a closed fist.

  • Location: Thoracic cavity, mediastinum (central core of thoracic cavity).

  • Orientation: Apex directed left; 2/3 mass left of midline of sternum.

6. Pericardium

  • Structure:

    • Fibrous pericardium: Tough outer layer prevents overdistention.

    • Serous pericardium: Thin inner layer with two parts:

      1. Parietal pericardium: lines fibrous layer.

      2. Visceral pericardium or epicardium: covers the heart surface.

  • Contains pericardial cavity with pericardial fluid.

7. Heart Wall Structure

  • Three layers:

    1. Epicardium: Outer smooth layer.

    2. Myocardium: Middle layer of cardiac muscle responsible for contraction.

    3. Endocardium: Smooth inner surface of heart chambers.

  • Structures: Pectinate muscles (auricles), Trabeculae carneae (ventricles).

8. External Anatomy

  • Comprised of two atria and two ventricles.

  • Blood entry: Through superior/inferior vena cava and pulmonary veins.

  • Blood exit: Through pulmonary trunk and aorta.

  • Surface grooves indicate coronary vessel locations.

9. Coronary Circulation: Arteries

  • Left Coronary Artery:

    • Anterior interventricular artery, left marginal artery, circumflex artery.

  • Right Coronary Artery: Smaller, with branches supplying right ventricle and posterior aspects.

10. Coronary Circulation: Veins

  • Great cardiac vein: Drains left-side blood.

  • Small cardiac vein: Drains right side.

  • Coronary sinus: Main collection point draining into right atrium.

11. Heart Chambers

  • Right Atrium: Recieves blood from the body.

  • Left Atrium: Receives blood from lungs.

  • Interatrial septum: Contains fossa ovalis, a fetal remnant.

  • Ventricles: Right opens to pulmonary trunk; left to aorta.

12. Heart Valves

A. Atrioventricular Valves (AV Valves)

  • Right (tricuspid) has three cusps; left (bicuspid/Mitral) has two.

B. Semilunar Valves

  • Shape like cups, open and close based on pressure changes during contraction and relaxation.

13. Blood Flow Through the Heart

  • Route from body to heart, from heart to lungs/body through respective veins and arteries.

14. Cardiac Muscle

  • Comprised of elongated, branching cells with striations.

  • Many mitochondria and a rich network of capillaries.

  • Intercalated disks: Specialized connections for cell communication.

15. Conducting System

  • SA Node: Pacemaker initiating heartbeats.

  • Action potentials relayed to AV Node, then through the AV bundle and fibers to ventricles, coordinating contractions.

16. Electrical Properties

  • Cardiac muscle cells maintain a resting membrane potential.

  • Autorhythmicity allows spontaneous action potentials.

17. Electrical Events: Electrocardiogram (ECG)

  • Waves: P wave (atrial depolarization), QRS (ventricular depolarization), T wave (ventricular repolarization).

18. Cardiac Cycle

  • Comprised of phases: Systole (contraction) and Diastole (relaxation).

A. Phases of Cardiac Cycle:

  1. Passive Filling: Blood enters heart passively.

  2. Atrial Systole: Atria contract for active filling.

  3. Ventricular Systole: Blood is ejected.

  4. Ventricular Diastole: Relaxation begins; blood fills ventricles.

19. Regulation of Heart Function

A. Intrinsic Regulation

  • Preload and Afterload influence cardiac output.

B. Extrinsic Regulation

  • Neural and hormonal influences affect heart rate and contraction strength.

20. Homeostasis and Heart Function

  • Baroreceptors and Chemoreceptors monitor and adjust heart function based on changes in blood pressure and gas levels.

21. Aging and Heart Function

  • Age-related changes include cardiac hypertrophy, increased arrhythmias.

22. Common Diseases and Disorders of the Heart

A. Conditions include

  • Endocarditis: Inflammation of the heart lining.

  • Coronary artery disease: Reduces blood flow to heart muscle.

  • Heart failure: Progressive weakening of heart muscle.

  • Congenital Heart Diseases: Present at birth affecting heart structures.

Note: Also included are implications of conditions like murmurs and stenosis on heart sounds.