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Recording-2025-03-13T15:05:12

Overview of Blood Flow Through the Heart

  • Two Circuits of Blood Flow

    • Systemic Circuit: Carries oxygen-rich blood from the heart to the body and returns oxygen-poor blood back to the heart.

    • Pulmonary Circuit: Carries oxygen-poor blood from the heart to the lungs for gas exchange and returns oxygen-rich blood back to the heart.

Blood Characteristics

  • Pulmonary Circuit produces oxygen-rich blood.

  • Systemic Circuit results in oxygen-poor blood.

  • Oxygen-poor blood is drained from organs via veins into:

    • Superior Vena Cava: Returns blood from the upper body.

    • Inferior Vena Cava: Returns blood from the lower body.

Right Atrium and Blood Flow

  • Deoxygenated blood enters the right atrium from:

    • Superior Vena Cava

    • Inferior Vena Cava

    • Coronary Sinus: Collects oxygen-poor blood from the heart itself.

  • Blood flows through the tricuspid valve into the right ventricle.

Right Ventricle and Pulmonary Circuit

  • Upon contraction, blood moves from the right ventricle through the pulmonary valve into the pulmonary trunk (an artery, despite appearing blue).

  • Pulmonary arteries branch off the trunk to carry blood to the lungs for gas exchange (CO2 exchange for O2).

Returning to the Heart

  • Oxygen-rich blood returns from lungs through pulmonary veins (despite appearing red, they are veins) into the left atrium.

  • Blood moves through the mitral (bicuspid) valve into the left ventricle.

Systemic Circuit Functionality

  • Left Ventricle contracts, ejecting oxygen-rich blood through the aortic valve into the aorta and the systemic circulation.

  • Oxygen delivery occurs via capillaries; resulting in oxygen-poor blood returning to the heart via the vena cavae.

Functions of Heart Valves

  • Atrioventricular Valves (AV): Prevent backflow from ventricles to atria (tricuspid & mitral valves).

  • Semilunar Valves: Prevent backflow from arteries to ventricles (pulmonary & aortic valves).

Cardiomyocytes (Cardiac Muscle Cells)

  • Cardiomyocytes: Form the myocardium, middle muscular layer that contracts to move blood.

  • Mechanism of Contraction: Uses the sliding filament mechanism (actin & myosin interaction) similar to skeletal muscle.

    • Requires calcium ions for cross-bridge formation.

  • Intercalated Discs:

    • Desmosomes: Mechanically hold cells together.

    • Gap Junctions: Allow for electrical communication between cardiomyocytes, facilitating synchronized contraction.

Cardiac Conduction System

  • Sinoatrial Node (SA Node): The heart's pacemaker; initiates impulse for heartbeat.

    • Fires, stimulating atrial contraction spread via gap junctions.

  • Atrioventricular Node (AV Node): Catches impulse from SA node, holding it briefly to allow complete atrial contraction before passing it down.

  • AV Bundle: Transmits impulse to bundle branches towards the ventricles.

  • Purkinje Fibers: Branch from bundle branches, spreading the impulse throughout the ventricles, coordinating contraction (apex to base).

Heart Rate Regulation

  • Central Nervous System (CNS): Influences heart rate via autonomic nervous system:

    • Sympathetic: Increases heart rate.

    • Parasympathetic: Decreases heart rate (normal resting rate between 60-100 bpm).

Cardiac Cycle

  • Systole and Diastole:

    • Systole: contracts to pump blood.

    • Diastole: relaxes, allowing chambers to fill with blood.

  • Phases of Cardiac Cycle:

    • Atrial Systole

    • Atrial Diastole

    • Ventricular Systole

    • Ventricular Diastole

Electrocardiogram (ECG)

  • P Wave: Electrical activity from SA node stimulating atrial depolarization.

  • QRS Complex: Ventricular depolarization (masking atrial repolarization).

  • T Wave: Ventricular repolarization, occurring while the heart relaxes.

Heart Rhythm and Disorders

  • Sinus Rhythm: Normal rhythm (60-100 bpm).

  • Ectopic Foci: Abnormal impulses firing before the SA node.

  • Heart Blocks: Impulses not properly transmitted between atria and ventricles, can lead to complications like ventricular fibrillation, which is life-threatening.