Cardiovascular System

Overview

• Components of the cardiovascular system:

  • Pump: the heart

  • Conducting hoses: blood vessels

  • Fluid connective tissue: blood

• Function: Move blood continuously around the body.

Circuits of the Cardiovascular System

• The cardiovascular system consists of two closed circuits:

  • Pulmonary Circuit: Carries blood to and from the gas exchange surfaces of lungs.

  • Systemic Circuit: Carries blood to and from the rest of the body.

• Each circuit begins and ends at the heart, travelling through:

  • Heart → Arteries → Arterioles → Capillaries → Venules → Veins.

Blood Vessels

• Types of Blood Vessels:

  • Arteries: Carry blood away from the heart; smallest are arterioles.

  • Veins: Return blood to the heart; smallest are venules.

  • Capillaries: Exchange vessels interconnecting smallest arteries and veins; responsible for gas, nutrient, and waste exchange.

Blood Characteristics

• Color representations in diagrams:

  • Blue: Deoxygenated blood

  • Red: Oxygenated blood

  • Purple: Mixture

• All blood is technically red; color varies from bright to dark red based on oxygen content.

Anatomy of the Heart

Heart Chambers

• Four Chambers of the Heart:

  • Right Atrium: Receives blood from systemic circuit.

  • Right Ventricle: Pumps blood into pulmonary circuit.

  • Left Atrium: Receives blood from pulmonary circuit.

  • Left Ventricle: Pumps blood into systemic circuit.

Structural Features

• Great Vessels: Connect at the base (superior) of the heart; apex is its pointed tip.

• Sits between the two pleural cavities within the mediastinum.

Pericardium

• Structure:

  • Outer fibrous pericardium

  • Inner serous pericardium

    • Outer parietal layer

    • Inner visceral layer (epicardium)

• Pericardial Cavity: Between parietal and visceral layers, containing pericardial fluid.

Function of Pericardial Fluid

• Functions include:

  • Nutrient diffusion into heart tissue

  • Lubrication of heart surfaces

  • Cushioning to protect the heart

  • Waste removal from heart tissue.

Heart Wall

Layers of the Heart Wall

• Three Distinct Layers:

  • Epicardium (Visceral layer): Covers the heart's surface.

  • Myocardium: Composed of cardiac muscle tissue.

  • Endocardium: Covers inner surfaces of heart, consists of simple squamous epithelium and areolar tissue.

Cardiac Muscle Anatomy

• Myocardium is arranged in:

  • Atrial musculature forming bands in a figure-eight pattern.

  • Ventricular musculature spiraling around the ventricles.

Function of Cardiac Muscle Arrangement

• Spiral arrangement provides efficient contraction:

  • Contraction pattern is from the sides into the center, enhancing blood ejection.

  • Support roles of connective tissues include:

    • Physically supporting muscle fibers

    • Distributing contraction forces

    • Preventing overexpansion

    • Providing elasticity for recovery after contraction.

Cardiac Skeleton

Structure and Function

• Consists of four dense bands of elastic tissue:

  • Stabilizes positions of heart valves and ventricular muscle cells.

  • Electrically insulates ventricular cells from atrial cells.

Superficial Anatomy of the Heart

• Two thin-walled atria with expandable auricles.

• Two thick-walled ventricles.

• Sulci (grooves) mark boundaries:

  • Coronary sulcus: between atria and ventricles.

  • Anterior and posterior interventricular sulci: separate left and right ventricles.

Major Anatomical Features

• Features include:

  • Ascending Aorta

  • Arch of Aorta

  • Pulmonary Trunk

  • Right atrium / ventricle

  • Left atrium / ventricle.

Heart Valves

Types of Heart Valves

• Atrioventricular Valves (AV):

  • Tricuspid Valve: Between right atrium and ventricle.

  • Mitral Valve (Bicuspid): Between left atrium and ventricle.

• Semilunar Valves:

  • Pulmonary Valve: Prevents backflow into right ventricle.

  • Aortic Valve: Prevents backflow into left ventricle.

Functionality

• Valves allow blood flow in one direction.

• Chordae tendineae prevent valve backflow during ventricular contraction.

Blood Flow Pathway

Right Atrium Blood Reception

• Receives blood from:

  • Superior vena cava: Blood from upper body.

  • Inferior vena cava: Blood from lower body.

  • Foramen ovale: Opening during fetal life that closes after birth forming fossa ovalis.

Right Ventricle Characteristics

• Contains:

  • Trabeculae carneae: Muscular ridges.

  • Conus arteriosus: Leads to pulmonary trunk and exits to pulmonary circuit.

Left Atrium and Ventricle Blood Flow

• Left Atrium: Receives blood from pulmonary veins, passes to left ventricle through mitral valve.

• Left Ventricle: Blood exits through the aortic valve into ascending aorta.; distributes to systemic circulation.

Cardiac Conduction System

Heartbeat Mechanism

• Cardiac contraction occurs in sequence:

  • Atria contract first, then ventricles.

• Autorhythmicity: Cardiac muscle can contract without external stimulation.

Components of the Conducting System

• Pacemaker Cells: Found in the Sinoatrial (SA) Node (right atrium) and Atrioventricular (AV) Node (junction of atria and ventricles).

• Conduction Pathway:

  • Impulse spreads to AV bundle, bundle branches, and Purkinje fibers, ensuring orderly contraction.

Electrocardiogram (ECG)

• Definition: A recording of electrical events in the heart, diagnostic for damage and arrhythmias.

• Key Components:

  • P Wave: Atrial depolarization.

  • QRS Complex: Ventricular depolarization.

  • T Wave: Ventricular repolarization.

Cardiac Cycle

Phases of the Cardiac Cycle

• Systole: Contraction phase, pressure rises.

• Diastole: Relaxation phase, pressure falls.

a. Blood flow controlled by timing of contractions.

• Importance of valves to maintain direction and pressure of blood flow.

Cardiac Output (CO)

• CO = HR × SV (Heart Rate × Stroke Volume).

• Reflects the volume pumped by the left ventricle in a minute.

Summary

• The cardiovascular system is essential for maintaining blood flow throughout the body, allowing for nutrient exchange, waste removal, and supporting overall heart function via complex structures and mechanisms.