Cardiovascular System Notes

Study Notes for Cardiovascular System

1. Introduction to the Cardiovascular System

  • Cardiovascular system consists of:

    • Heart

    • Blood vessels

  • Functionality:

    • The heart pumps blood into blood vessels, circulating blood throughout the body.

    • Blood is responsible for transporting nutrients and oxygen to tissues and removing carbon dioxide and waste products.

1.1. The Heart

  • Structure:

    • Muscular organ situated between the lungs in the mediastinum, composed of four chambers (2 atria, 2 ventricles).

    • Musculature:

    • Ventricles have thicker walls compared to atria, contributing to their contraction force.

    • Contraction force relies on muscular integrity.

1.2. Right Side of the Heart

  • Chambers & Functionality:

    • Right Atrium:

    • Thin-walled, low-pressure chamber.

    • Contains pacemaker (sinoatrial node) producing cardiac impulses and atrioventricular node conducting impulses to ventricles.

    • Receives deoxygenated blood via:

      1. Superior vena cava (from head, neck, upper limbs)

      2. Inferior vena cava (from lower body)

    • Right Ventricle:

    • Thick-walled chamber.

    • Blood enters from the right atrium via the tricuspid valve.

    • Pumps deoxygenated blood to lungs via the pulmonary artery where it gets oxygenated.

1.3. Left Side of the Heart

  • Chambers & Functionality:

    • Left Atrium:

    • Thin-walled, receives oxygenated blood from the lungs via pulmonary veins.

    • Exception: arteries carry deoxygenated blood, veins carry oxygenated blood.

    • Blood flows to the left ventricle through the mitral (bicuspid) valve.

    • Left Ventricle:

    • Very thick-walled to pump oxygenated blood to entire body via the aorta.

1.4. Septa of the Heart

  • Division:

    • Interatrial Septum: Separates right and left atria.

    • Interventricular Septum: Separates left and right ventricles, comprising a membranous upper part and muscular lower part.

1.5. Layers of the Heart Wall

  • Heart consists of three layers:

    1. Pericardium (outer layer)

    2. Myocardium (middle layer)

    3. Endocardium (inner layer)

1.6. Pericardium

  • Structure:

    • Made of two layers (parietal and visceral pericardium).

    • Pericardial cavity contains 25 to 35 mL of fluid preventing friction.

1.7. Myocardium

  • Properties:

    • Composed of cardiac muscle fibers (myocytes); responsible for heart's pumping action.

    • Types of Muscle Fibers in myocardium:

    1. Contractile fibers

    2. Pacemaker fibers

    3. Conductive system fibers

1.8. Endocardium

  • Thin, smooth membrane lining the inner surface of the heart, continuous with the endothelium of blood vessels.

1.9. Heart Valves

  • Atrioventricular Valves:

    • Mitral (Bicuspid) valve (left heart)

    • Tricuspid valve (right heart)

  • Semilunar Valves:

    • Aortic valve (between left ventricle and aorta)

    • Pulmonary valve (between right ventricle and pulmonary artery)

1.10. Actions of the Heart

  • Types:

    1. Chronotropic action: Heart rate variation

    2. Inotropic action: Force of contraction variation

    3. Dromotropic action: Impulse conduction variation

    4. Bathmotropic action: Cardiac muscle excitability variation

2. Properties of Cardiac Muscle

2.1. Excitability

  • Definition: Ability of cardiac tissue to respond to a stimulus.

  • Initial stimulus produces electrical activity as action potential followed by mechanical activity (contraction).

2.2. Electrical Potentials in Cardiac Muscle

  • Resting membrane potential:

    • Cardiac muscle fiber: -85 to -95 mV

    • SA node: -55 to -60 mV

    • Purkinje fibers: -90 to -100 mV

  • Action Potential Duration: 250-350 msec.

2.3. Spread of Action Potential

  • Rapid spread facilitated by gap junctions allowing ion movement between cardiac muscle fibers.

2.4. Rhythmicity

  • Definition: Heart's ability to regularly produce its own impulses, primarily attributed to the SA node.

2.5. Conductive System

  • Components include SA node, AV node, Bundle of His, bundle branches, and Purkinje fibers.

  • Impulse transmission from the SA node to ventricles is facilitated through the conductive system.

2.6. Contractility

  • The strength of contraction increases with preload due to the Frank-Starling mechanism.

  • Describes the heart's ability to adjust the force of contraction based on the end-diastolic volume.

3. Cardiac Cycle

3.1. Definition

  • A series of events during each heartbeat, composed of systole (contraction) and diastole (relaxation).

3.2. Phases of Cardiac Cycle

  • Atrial systole, ventricular systole (including isometric contraction and ejection period), and diastole.

  • Right atrial pressure influences blood flow into the ventricles.

4. Heart Sounds

4.1. Types of Heart Sounds

  1. First sound (S1): Closure of AV valves during isometric contraction.

  2. Second sound (S2): Closure of semilunar valves; marks end of systole.

  3. Third sound (S3): Caused by rapid filling of ventricles, often inaudible under normal conditions.

  4. Fourth sound (S4): Caused by atrial contraction against a stiff ventricle, typically inaudible except under pathological conditions.

4.2. Methods of Study

  • Heart sounds can be characterized using a stethoscope, microphone, and graphical recording (phonocardiogram).

5. Electrocardiogram (ECG)

5.1. Definition

  • A graphical representation of the electrical activity of the heart.

5.2. Importance

  • Used to diagnose heart rhythm, size/position of heart chambers, damage to heart areas, heart attacks, and cardiac health overall.

5.3. Components

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

  • Intervals: PR interval, QT interval, etc.

6. Hemodynamics

6.1. Introduction

  • Study of blood flow dynamics in the cardiovascular system.

6.2. Key Concepts

  • Mean volume of blood flow, types of blood flow (laminar vs turbulent), pressure gradient and its influence, factors affecting blood flow include radius, viscosity, and pressure.

7. Cardiac Output

7.1. Definitions and Measurement

  • Cardiac output: Volume of blood pumped by the heart per minute.

  • Measured via direct methods (invasive) or indirect methods (non-invasive).

7.2. Definition of Key Terms

  • Stroke Volume: Blood ejected per heartbeat, typically 70 mL.

  • Minute Volume: Total blood pumped per minute, typically 5 L.

  • Ejection Fraction: Percentage of blood ejected from ventricles, typically 60-65%.

8. Effect of Changes in Electrolyte Concentration on Heart

8.1. Influence of Sodium, Potassium, Calcium

  • Changes in these electrolytes affect cardiac excitability, contractility, and overall function.

8.2. Physiological Response

  • Hyperkalemia: High potassium reduces excitability; hypokalemia: low potassium increases sensitivity and alters ECG characteristics.

9. Arrhythmia

9.1. Definitions and Types

  • Irregular heartbeats range from fast (tachycardia) to slow (bradycardia) patterns.

9.2. Mechanisms

  • Can arise from underlying cardiac pathology or as a physiological response to stimuli.

9.3. Clinical Implications

  • Requires monitoring and possible intervention based on type and severity.

10. Conclusion

  • Understanding the cardiovascular system's components and functions is essential for diagnosing and treating related conditions efficiently.