CARDIO

Cardiovascular System Overview

  • The cardiovascular system consists of the heart and blood vessels, responsible for circulating blood and facilitating gas exchange.

Anatomy of the Heart

  • Location: The heart is situated in the mediastinum.

Structure and Layers of the Heart

  • Pericardium: A double-walled sac containing the heart; consists of:

    • Parietal Layer: Outer layer

    • Visceral Layer (Epicardium): Covers the heart

    • Pericardial Cavity: Contains serous fluid to reduce friction during heartbeats.

  • Heart Wall: Composed of three layers:

    • Epicardium: Outer layer

    • Myocardium: Middle muscular layer (thickest)

    • Endocardium: Inner lining of the heart chambers.

Chambers of the Heart

  • Four Chambers:

    • Atria (2 superior chambers)

    • Ventricles (2 inferior chambers)

  • Septum: Divides the heart into right and left sides.

    • Interatrial Septum: Separates the atria

    • Interventricular Septum: Separates the ventricles.

Blood Vessels Related to the Heart

  • Right Atrium receives blood from:

    • Superior Vena Cava: Drains blood from the upper body

    • Inferior Vena Cava: Drains blood from the lower body

    • Coronary Sinus: Drains blood from the heart.

  • Left Atrium receives blood from:

    • Pulmonary Veins: Carry oxygenated blood from the lungs.

  • Right Ventricle pumps blood to:

    • Pulmonary Artery: Carries deoxygenated blood to the lungs.

  • Left Ventricle pumps blood to:

    • Aorta: Distributes oxygenated blood to the body.

Heart Valves

  • Tricuspid Valve: Between right atrium and right ventricle.

  • Pulmonary Valve: Between right ventricle and pulmonary artery.

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

  • Aortic Valve: Between left ventricle and aorta.

  • Function: Prevent backflow of blood during heart contraction.

Cardiac Muscle Tissue

  • Structure: Composed of branching cells connected by intercalated discs which include:

    • Desmosomes: Provide structural support.

    • Gap Junctions: Allow electrical impulses to pass between cells, facilitating rapid contraction.

Cardiac Conduction System

  • Components: SA Node, AV Node, Bundle of His, Purkinje Fibers.

  • Function: Facilitates pacemaker activity and coordinates heart contractions.

  • SA Node: Pacemaker of the heart, generates impulses at a rate of 70-100 beats/min.

Action Potential in Cardiac Muscle

  • Phases:

    • Phase 0: Rapid depolarization via Na+ influx.

    • Phase 1: Initial repolarization.

    • Phase 2: Plateau phase due to Ca2+ influx.

    • Phase 3: Repolarization via K+ efflux.

    • Phase 4: Resting membrane potential.

ECG (Electrocardiogram)

  • Records electrical activity of the heart:

    • P Wave: Atrial depolarization.

    • QRS Complex: Ventricular depolarization.

    • T Wave: Ventricular repolarization.

Cardiac Cycle

  • Definition: Series of events during one heart beat including systole (contraction) and diastole (relaxation).

  • Events During Systole:

    • Isovolumic Contraction: Ventricles contract, no volume change.

    • Ejection Phase: Blood is expelled into arteries.

  • Events During Diastole:

    • Isovolumic Relaxation: ventricles relax; pressure drops.

    • Rapid Inflow: Blood fills ventricles via AV valves.

Cardiac Output

  • Formula: CO = Stroke Volume x Heart Rate.

  • Typical Values: 70 mL/beat (SV) and 75 beats/min (HR) gives an average CO of 5.25 L/min.

Regulation of Heart Function

  • Stroke Volume Factors:

    • Preload: Degree of stretch before contraction.

    • Contractility: Force of contraction.

    • Afterload: Resistance the ventricle must overcome to eject blood.

  • Heart Rate Factors:

    • Affected by autonomic nervous system and hormones (epinephrine increases HR).

Blood Vessel Anatomy and Functions

  • Types: Elastic arteries, muscular arteries, arterioles, capillaries, venules, and veins.

  • Functionality: Vessels conduct, distribute, and exchange blood with tissues.

Blood Pressure and Resistance

  • Definition: BP is the force exerted by circulating blood against blood vessel walls.

  • Factors Affecting BP: Vessel lumen size, blood viscosity, and total vessel length.

Shock Types

  • Hypovolemic Shock: Due to reduced blood volume.

  • Cardiogenic Shock: Due to heart failure.

  • Vascular Shock: Due to inappropriate vasodilation.

  • Obstructive Shock: Due to physical blockage of blood flow.

Homeostatic Responses to Shock

  • Renin–angiotensin system responds to reduced BP to restore blood volume and pressure.

  • Activation of sympathetic response and release of local vasodilators helps adjust blood flow during stress.

Summary of Important Hormones

  • Epinephrine/Norepinephrine: Increases heart rate and force of contraction.

  • ADH: Increases blood volume by promoting water reabsorption.

  • ANP: Decreases blood volume and pressure.

  • Inotropic Agents: Affect contractility positively or negatively.

Important Concepts:

  • Frank-Starling Law: The more the heart is stretched (higher EDV), the stronger the contraction.