Cardiovascular

Chapter 25: Structure and Function of the Cardiovascular and Lymphatic Systems

Overview of the Cardiovascular System

  • Circulatory System

    • Right heart

    • Pulmonary circulation

      • Function: Pumps deoxygenated blood through the lungs via the pulmonary artery.

    • Left heart

    • Systemic circulation

      • Function: Pumps oxygenated blood through the body via the pulmonary veins.

Anatomy of the Heart

  • Heart Structure

    • Valves

    • Tricuspid valve: Located between the right atrium and right ventricle

    • Mitral valve (Bicuspid): Located between the left atrium and left ventricle

    • Pulmonary valve: Located between the right ventricle and pulmonary artery

    • Aortic valve: Located between the left ventricle and aorta

    • Heart chambers

    • Atria: Right atrium, left atrium

      • Characteristics: Smaller with thinner walls

    • Ventricles: Right ventricle, left ventricle

      • Characteristics: Thicker myocardial layer

Blood Flow Through the Heart

  • Oxygen-poor blood follows this pathway:

    1. Superior vena cava

    2. Inferior vena cava

    3. Right atrium

    4. Tricuspid valve

    5. Right ventricle

    6. Pulmonary valve

    7. Pulmonary arteries

    8. Lungs (oxygenation)

  • Oxygen-rich blood follows this pathway:

    1. Pulmonary veins

    2. Left atrium

    3. Mitral valve

    4. Left ventricle

    5. Aortic valve

    6. Aorta

Heart Valves

  • Types of Valves

    • Atrioventricular valves

    • Tricuspid valve (right heart)

    • Mitral valve (left heart)

    • Composition: Openings composed of tissue flaps

    • Semilunar valves

    • Pulmonary semilunar valve

    • Aortic semilunar valve

    • Composition: Openings composed of cup-shaped cusps

Blood Flow and Cardiac Cycle

  • Pressure Gradients

    • Blood flows in one direction due to pressure differences.

  • Cardiac Cycle Phases

    • Diastole (ventricles relaxed)

    • Higher pressure in atria than in ventricles

    • Systole (ventricles contracted)

    • Ventricle pressure increases, closing valves to prevent backflow.

    • Semilunar valves open when pressure in the ventricles exceeds that in the aorta/pulmonary artery.

Electrical Conduction System of the Heart

  • Electrocardiogram (ECG) Deflections

    • P: Atrial depolarization.

    • QRS complex: Ventricular depolarization and atrial repolarization.

    • T: Ventricular repolarization.

  • ECG Intervals

    • P-R Interval: 0.12-0.20 seconds

    • Q-T Interval: Under 0.38 seconds

    • S-T Interval: Determines myocardial ischemia

Cardiac Output

  • Definition: The amount of blood the heart pumps in one minute.

  • Formula: Cardiac Output = Heart Rate x Stroke Volume

  • Normal adult cardiac output:

    • Approximately 5 L/minute

  • Ejection Fraction:

    • Formula: Ejection Fraction = Stroke Volume / End-Diastolic Volume

Factors Affecting Cardiac Output

  • Preload (The stretch): Volume/pressure inside the ventricle at end of diastole

    • Frank-Starling Law: The more the heart is filled during diastole, the greater the force of contraction during systole.

  • Afterload (The push): Resistance to ejection of blood, determined by systemic vascular resistance (SVR) in the aorta.

  • Contractility: Strength of heart muscle contractions, affected by inotropic agents.

  • Heart Rate:

    • Controlled by reflexes, hormones and neural inputs (e.g., baroreceptor reflexes, Bainbridge reflex).

Structure of Blood Vessels

  • Arterial Vessels:

    • Function: Carry oxygenated blood away from the heart (red in diagrams).

    • Types: Arteries, arterioles, metarterioles, capillaries.

  • Venous Vessels:

    • Function: Carry deoxygenated blood toward the heart (blue in diagrams).

    • Types: Veins, venules.

Factors Affecting Blood Flow

  • Pressure: Force exerted on liquid per unit area.

  • Resistance: Opposition to flow, influenced by blood vessel diameter and length.

  • Velocity: Speed of blood flow through the vessels.

  • Vascular Compliance: Ability of a vessel to accommodate an increase in volume.

  • Types of Flow:

    • Laminar: Smooth and orderly flow (parabolic profile).

    • Turbulent: Irregular flow resulting in murmurs.

Lymphatic System

  • Components:

    • Thymus, Lymph Nodes (Cervical, Axillary, Inginal), Bone Marrow, Spleen

    • Ducts: Right lymphatic duct, Thoracic duct, Right subclavian vein, Left subclavian vein.

Diseases of the Veins

  • Varicose Veins:

    • Characteristics: Pooling, distended, tortuous, palpable veins.

    • Risk Factors: Age, female gender, family history, obesity, pregnancy, prior leg injury.

  • Chronic Venous Insufficiency:

    • Definition: Inadequate venous return over a long period.

  • Thrombus Formation in Veins:

    • Thrombus: attached clot, Thromboembolus: detached clot.

    • Virchow's Triad: Components that promote thrombosis - venous stasis, endothelial damage, hypercoagulable states.

  • Superior Vena Cava Syndrome:

    • Symptoms: Venous distention in upper extremities and head caused by progressive occlusion.

Hypertension

  • Definition: Consistent elevation of systemic arterial blood pressure.

    • Systolic pressure ≥ 130 mm Hg or Diastolic pressure ≥ 80 mm Hg.

  • Primary Hypertension (Essential):

    • Multifactorial with genetic and environmental factors impacting 92-95% of patients. Risk Factors include:

    • Family history

    • Diet (high sodium, low potassium, calcium, magnesium)

    • Tobacco and alcohol

    • Obesity, glucose intolerance.

  • Secondary Hypertension:

    • Causes include renal vascular disease, endocrine tumors, and drug effects.

  • Complicated Hypertension:

    • Chronic hypertensive damage resulting in target organ damage (heart, kidney, brain).

  • Hypertensive Crisis:

    • Systolic > 180 mm Hg or Diastolic > 120 mm Hg, considered life-threatening.

Aneurysm

  • Definition: Local dilation or outpouching of a vessel wall or cardiac chamber.

  • True Aneurysms:

    • Involves weakening of all three layers of the vessel wall.

  • False Aneurysms:

    • Extravascular hematoma that communicates with the intravascular space.

  • Most Susceptible Site: Aorta, particularly abdominal aorta.

    • Causes: atherosclerosis, hypertension leading to dissections or ruptures.

Hypotension

  • Orthostatic Hypotension:

    • Definition: Decrease in blood pressure upon standing.

    • Can be acute or chronic; related to conditions like Addison's Disease.

Thrombus Formation

  • Definition: Blood clot remaining attached to the vessel wall.

  • Risk Factors: Intimal injury, flow obstruction, stasis.

Embolism

  • Definition: Bolus of matter circulating in the bloodstream, can include:

    • Dislodged thrombus, air, fat aggregates, bacteria, cancer cells.

Peripheral Vascular Disease

  • Thromboangiitis Obliterans (Buerger Disease):

    • Autoimmune disease affecting peripheral arteries, associated with smoking.

  • Raynaud Phenomenon:

    • Episodic vasospasm in finger and toe arteries.

    • Can be primary (unknown origin) or secondary to other conditions.

Arteriosclerosis

  • Definition: Chronic disease characterized by abnormal thickening and hardening of vessel walls due to smooth muscle cell migration to the tunica intima.

Atherosclerosis

  • Definition: A form of arteriosclerosis, defined by lipid accumulation within arterial walls leading to plaque formation.

  • Risk Factors: Diabetes, smoking, hypertension, autoimmunity.

  • Progression: Involves inflammation of endothelium, cellular proliferation, macrophage migration, LDL oxidation.

Peripheral Arterial Disease

  • Definition: Atherosclerosis in the arteries perfusing limbs.

  • Symptoms: Intermittent claudication (pain in limbs due to ischemia).

Coronary Artery Disease

  • Definition: Vascular disorder leading to myocardial ischemia due to narrowing or occlusion of coronary arteries.

  • Major Risk Factors: Increased age, family history, gender, dyslipidemia, hypertension.

  • Manifestations of Ischemia:

    • Silent ischemia, stable angina, Prinzmetal angina.

  • Acute Coronary Syndromes: Include unstable angina and myocardial infarction.

Myocardial Infarction

  • Definition: Extended obstruction of myocardial blood supply leading to myocardial necrosis.

  • Types: STEMI (ST elevation) and Non-STEMI.

  • Manifestations:

    • Sudden severe chest pain, nausea, diaphoresis, dyspnea.

Disorders of the Pericardium

  • Acute Pericarditis: Inflammation of the pericardial membrane causing sharp pain.

  • Pericardial Effusion: Fluid buildup in the pericardial sac, can lead to tamponade.

  • Constrictive Pericarditis: Results from scarring and loss of elasticity.

Disorders of the Myocardium

  • Cardiomyopathies:

    • Dilated, hypertrophic (obstructive/hypertensive), and restrictive cardiomyopathy.

Disorders of the Endocardium

  • Valvular Dysfunctions:

    • Stenosis or regurgitation (backward flow) of valves, including mitral and aortic valves.

    • Mitral Valve Prolapse: Upward bulging of mitral valve cusps into the left atrium during systole.

    • Rheumatic Fever: Inflammatory disease linked with previous streptococcal infection.

    • Infective Endocarditis: Inflammation due to infection by various agents, leading to cardiac damage.

Heart Failure

  • Definition: Inability of the heart to generate adequate cardiac output.

    • Increased diastolic pressure and pulmonary capillary pressures.

  • Left Heart Failure:

    • Systolic: Ejection fraction <40%; causes dyspnea, fatigue, regurgitation.

    • Diastolic: Pulmonary congestion despite normal stroke volume; associated with hypertrophy and ischemia.

  • Right Heart Failure:

    • Inability to effectively pump blood, often due to left heart pressure increase.

Shock

  • Definition: Cardiovascular system fails to adequately perfuse tissues, leading to metabolic impairment.

  • Types of Shock:

    • Cardiogenic: Heart failure.

    • Hypovolemic: Insufficient fluid volume.

    • Neurogenic: Loss of vascular tone.

    • Anaphylactic: Severe allergic reactions.

    • Septic: Triggered by infection; leads to systemic inflammatory response.

Multiple Organ Dysfunction Syndrome (MODS)

  • Definition: Progressive dysfunction of two or more organ systems from uncontrolled inflammatory responses.

    • Common causes: sepsis, severe trauma, and major surgery.