Cardio CH 19

Cardiovascular System Overview

• Cardiology: Study of the heart and its disorders.

• Components:

  • Heart: Functions as a pump to circulate blood through vessels.

  • Blood Vessels: Deliver blood to tissues and return it to the heart.

    • Arteries: Carry blood away from the heart.

    • Veins: Carry blood toward the heart.

    • Capillaries: Microscopic vessels connecting arteries and veins.

• Circulatory system: Encompasses heart, vessels, and blood.

Circuits of the Cardiovascular System

1. Major Divisions

• Pulmonary Circuit: Carries blood to lungs for gas exchange and back to the heart.

• Systemic Circuit: Supplies oxygenated blood to all body tissues and returns deoxygenated blood to the heart.

2. Blood Flow Dynamics

• Right Heart: Supplies pulmonary circuit; oxygen-poor blood arrives from tissues and is sent to lungs via pulmonary arteries.

• Left Heart: Supplies systemic circuit; oxygen-rich blood is sent to body tissues via the aorta.

The Pericardium

• Encloses the heart and consists of two layers:

  • Fibrous Pericardium: Tough outer layer providing structural support.

  • Serous Pericardium: Divided into:

    • Parietal Layer: Lines the fibrous pericardium.

    • Visceral Layer (Epicardium): Adheres to heart surface.

• Pericardial Cavity: Space between layers filled with 5-30 mL of fluid.

• Pericarditis: Inflammation of the pericardium; may result from infections or autoimmune diseases.

Heart Wall Structure

• Three Layers of the Heart:

  • Epicardium: Outer layer, includes serous membrane and adipose tissue.

  • Myocardium: Thick middle layer of cardiac muscle, facilitating contraction.

  • Endocardium: Smooth inner lining covering heart and valve surfaces, continuous with blood vessels.

• Fibrous Skeleton: Provides support, insulation, and anchors for muscle and valves.

Heart Chambers

• Chambers: Four in total - two atria and two ventricles.

1. Atria

• Right Atria: Receives deoxygenated blood; contains pectinate muscles.

• Left Atria: Receives oxygenated blood from lungs.

2. Ventricles

• Right Ventricle: Pumps blood to lungs; thinner wall.

• Left Ventricle: Pumps blood to body; wall is thicker due to increased workload.

Heart Valves

• Function: Ensure one-way blood flow through the heart.

  • Atrioventricular (AV) Valves: Control blood flow between atria and ventricles.

    • Right AV Valve (Tricuspid) and Left AV Valve (Mitral).

  • Semilunar Valves: Control flow from ventricles into major arteries.

    • Pulmonary Valve: Between right ventricle and pulmonary trunk.

    • Aortic Valve: Between left ventricle and aorta.

Blood Flow Through the Heart

1. Blood enters right atrium via superior and inferior venae cavae.

2. Flows through right AV valve into right ventricle.

3. Right ventricle contracts, forcing pulmonary valve open.

4. Blood enters pulmonary trunk and distributes to lungs for oxygenation.

5. Oxygenated blood returns to left atrium via pulmonary veins.

6. Flows through left AV valve into left ventricle.

7. Left ventricle contracts and forces aortic valve open, distributing blood throughout the body.

Coronary Circulation

• Definition: Blood supply to the myocardium.

• Arteries:

  • Left Coronary Artery (LCA):

    • Anterior Interventricular Branch (LAD): Supplies ventricles and anterior septum.

    • Circumflex Branch: Supplies left atrium and posterior ventricle.

  • Right Coronary Artery (RCA):

    • Supplies right atrium and ventricle.

• Flow Dynamics: Greatest during heart relaxation; coronary arteries compress during contraction.

Cardiac Muscle Physiology

• Energy Metabolism: Relies on aerobic respiration; high in myoglobin and glycogen.

• Adaptability: Utilizes various fuels including fatty acids and glucose.

• Fatigue Resistance: Rarely fatigues due to limited anaerobic fermentation.

Cardiac Conduction System

• Components:

  • Sinoatrial (SA) Node: Primary pacemaker initiating heartbeats at approx. 75 bpm.

  • Atrioventricular (AV) Node: Gateway to ventricles, delaying signals for proper timing.

  • Bundle Branches and Purkinje Fibers: Conduct electrical impulses throughout the ventricles.

• Electrical Activity: Coordinates heartbeat and ensures effective contraction.

Heart Rhythm and Function

• Sinus Rhythm: Normal heartbeat initiated by SA node.

• Ectopic Focus: Other regions can take over if SA node is damaged, leading to varied heart rates.

Electrocardiogram (ECG)

• Definition: Recording of electrical signals in the heart.

  • P Wave: Atrial depolarization.

  • QRS Complex: Ventricular depolarization.

  • T Wave: Ventricular repolarization just before diastole.

Cardiac Cycle Phases

1. Ventricular Filling: Blood flows into ventricles.

2. Isovolumetric Contraction: Ventricles contract without ejecting blood.

3. Ventricular Ejection: Blood is forced out into arteries.

4. Isovolumetric Relaxation: Ventricles relax and pressures change.

Cardiovascular Disorders

1. Coronary Artery Disease (CAD)

• Condition caused by atherosclerosis; obstruction can lead to heart attacks.

• Risk Factors: High LDL, hypertension, obesity.

2. Angina and Heart Attack

• Angina Pectoris: Chest pain due to reduced blood flow.

• Myocardial Infarction: Sudden loss of blood flow; caused by atheroma.