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Ch.19 Notes

Overview of the Cardiovascular System

  • Cardiovascular System Components: Comprises the heart and blood vessels.

  • Circulatory System Functions: Includes the heart, blood vessels, and the blood.

The Pulmonary and Systemic Circuits

Major Divisions

  • Pulmonary Circuit:

    • Right side of the heart.

    • Transfers oxygen-poor blood to lungs for gas exchange and back.

  • Systemic Circuit:

    • Left side of the heart.

    • Supplies oxygenated blood to all tissues of the body.

Blood Flow

  • Right Side of Heart: Oxygen-poor blood arrives from inferior and superior venae cavae and is sent to lungs via pulmonary trunk.

  • Left Side of Heart: Oxygenated blood arrives from lungs via pulmonary veins and is sent to all body organs via aorta.

Blood Flow Through the Chambers

  • Blood pathway: Right atrium → pulmonary circuit → systemic circuit → back to the heart.

Coronary Circulation

  • Heart receives about 5% (250 mL/min) of blood pumped to sustain its workload. Requires abundant O2 and nutrients.

Myocardial Infarction and Blood Supply

  • Myocardial Infarction (MI): Caused by interruption of blood supply, leading to cardiac cell death.

  • Coronary Arteries supply blood to the heart muscle and can be obstructed by atheromas (fatty deposits).

  • Blood flow greatest during heart relaxation (diastole).

Angina and Heart Attack

  • Angina Pectoris: Chest pain due to partial blood flow obstruction.

  • MI: Sudden death of cardiac patches due to long-term obstruction; symptoms include heavy pressure pain, sometimes radiating to the left arm.

Structure of Cardiac Muscle

  • Cardiomyocytes: Striated, short, thick, branched cells with a single central nucleus.

  • Intercalated Discs: Connect cardiomyocytes with junctions for mechanical (desmosomes) and electrical (gap junctions) communication.

  • Repair Mechanism: Limited to fibrosis (scarring).

Cardiac Muscle Metabolism

  • Relies almost exclusively on aerobic respiration for ATP production.

  • Contains high myoglobin and glycogen levels, with large mitochondria.

The Conduction System

Components

  • SA Node: Pacemaker in right atrium initiates heartbeat.

  • AV Node: Gateway to ventricles; delays the electrical signal to allow for ventricular filling.

  • Bundle of His & Purkinje Fibers: Distributes electrical signals, causing ventricles to contract in unison.

Nerve Supply to the Heart

  • Sympathetic Nerves: Increase heart rate and contraction strength; pathway originates from spinal cord.

  • Parasympathetic Nerves: Slow heart rate via vagus nerve.

Cardiac Cycle Phases

  1. Ventricular Filling: Blood flows into ventricles; pressures drop.

  2. Isovolumetric Contraction: Ventricles contract, but no blood ejection occurs.

  3. Ventricular Ejection: Blood is ejected when ventricle pressure exceeds arterial pressure.

  4. Isovolumetric Relaxation: Ventricles relax and pressure falls.

Heart Sounds

  • S1 (lubb): Closure of AV valves.

  • S2 (dupp): Closure of semilunar valves.

Stroke Volume and Effects

  • Stroke volume (SV) is influenced by preload, contractility, and afterload.

    • Preload: Tension before contraction.

    • Contractility: Force of contraction for a given preload.

    • Afterload: Resistance that ventricles must overcome to eject blood.

Coronary Artery Disease (CAD)

  • Results from atherosclerosis, leading to narrowed coronary arteries.

  • Symptoms include angina due to 75% or more obstruction.

  • Treatment options include coronary bypass surgery and angioplasty.

Risk Factors for CAD

  • Unavoidable: Heredity, aging, male gender.

  • Preventable: Obesity, smoking, inactivity, diet, and stress.