book

  • Heart Rhythmicity

    • Contracts at about 75 beats per minute (BPM) in resting adults

    • Triggers heartbeat via invertebrate pacemaker or myogenic in vertebrates

  • Cardiac Muscle Structure

    • Cardiac muscle is striated, short, thick, branched (50-100 μm long, 10-20 μm wide)

    • Cardiomyocytes connect via intercalated discs:

    • Interdigitating folds for surface area

    • Fascia adherens for actin anchoring

    • Desmosomes to prevent pulling apart

    • Gap junctions for electrical stimulation

  • Cardiac Muscle Metabolism

    • Relies on aerobic respiration, rich in myoglobin and glycogen

    • Energy source breakdown: ~60% from fatty acids, ~35% from glucose

    • Less prone to fatigue due to low anaerobic reliance

  • Cardiac Conduction System

    • Includes SA node (pacemaker), AV node, bundle branches, and Purkinje fibers

    • Pacemaker potential gradually depolarizes to initiate heartbeat

    • Sequence of excitation: SA → AV → Ventricles

  • Heart Cycle Phases

    • Systole: contraction phase; push blood out

    • Diastole: relaxation phase; chambers fill

    • Normal sinus rhythm occurs via the SA node

    • Abnormal rhythms (ectopic focuses, nodal rhythms) lead to arrhythmias

  • Electrocardiogram (ECG)

    • Represents electrical activity of heart with P wave, QRS complex, and T wave

    • Abnormalities indicate various cardiac conditions (e.g., arrhythmias)

  • Cardiac Output (CO)

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

    • Regulated by autonomic nerve influences:

    • Sympathetic (increases HR)

    • Parasympathetic (decreases HR)

  • Stroke Volume Influencers

    • Preload: tension in ventricles before contraction

    • Contractility: strength of muscle contraction

    • Afterload: pressure against which the heart must pump

    • Conditions like hypertension increase afterload

  • Influencing Factors

    • Hormones (e.g., epinephrine) and drugs affect heart rate/contraction

    • Electrolyte levels significantly influence cardiomyocyte function

  • Heart Sounds

    • S1 (lub) and S2 (dub) correlate with valve closure

    • Presence of S3 indicates potential heart dysfunction

  • Chronic Heart Conditions

    • Heart failure can lead to edema and other health issues

    • Exercise improves heart function and increases cardiac reserve

    • Understand and manage chronic conditions affecting heart health.