Heart Study Guide 2

HEART Anatomy and Circulation

Pulmonary Circuit

  • Right Side of the Heart:

    • Transports oxygen-poor blood from the body to the lungs for reoxygenation.

Systemic Circuit

  • Left Side of the Heart:

    • Transports fully oxygenated blood from the lungs to the organs throughout the body.

Heart Anatomy

  • Location: Mediastinum area of the thoracic cavity.

  • Base vs Apex:

    • Base: Broader top part of the heart.

    • Apex: Pointed bottom part of the heart, facing downwards and to the left.

  • Pericardium:

    • A sac that encloses the heart to reduce friction.

    • Composed of two layers:

    1. Parietal Pericardium: Superficial layer.

    2. Visceral Pericardium (Epicardium): Covers the heart.

    • Pericardial Fluid: Located between the parietal and visceral layers, reduces friction.

    • Pericarditis: Painful inflammation of the pericardial membranes.

Heart Wall Structure

  • Epicardium: Visceral pericardium.

  • Myocardium:

    • Cardiac muscle arranged in a spiral formation, responsible for the heart's pumping motion, akin to ‘wringing out a towel.’

  • Endocardium:

    • Covers the interiors of the heart chambers and valves; continuous with the endothelium of blood vessels.

Chambers of the Heart

  • Total: 4 chambers

    • Atria (Left and Right):

    • Superior chambers that receive returning blood.

    • Right Atria: Receives blood from the vena cava (from body).

    • Left Atria: Receives blood from the lungs via pulmonary veins.

    • Ventricles (Left and Right):

    • Inferior chambers that pump blood into the arteries.

    • Right Ventricle: Receives blood from the right atria, pumps it to the lungs via pulmonary arteries.

    • Left Ventricle: Receives blood from the left atria, pumps it to the body via aorta.

Valves of the Heart

  • Function: Act as one-way doors controlling blood flow.

  • Atrioventricular (AV) Valves: Control blood flow from atria to ventricles.

    • S1 "Lubb" Sounds

    • Right Side: Three cusps, known as Tricuspid Valve.

    • Left Side: Two cusps, known as Bicuspid or Mitral Valve.

  • Chordae Tendineae: Connect valves to papillary muscles, preventing bulging/backflow (prolapse).

  • Semilunar Valves: Control blood flow into arteries based on pressure.

    • S2 "Dupp" Sounds

    • Pulmonary Semilunar Valve: From right ventricle to lungs.

    • Aortic Semilunar Valve: From left ventricle to body.

Disorders of Heart Valves

  • Heart Murmurs: Audible sounds due to turbulent blood flow.

  • Insufficiency:

    • Valves fail to close properly, leading to backflow/regurgitation.

    • Common condition: Mitral Valve Prolapse (MVP).

  • Stenosis:

    • Valve becomes hardened, failing to open completely.

    • Common condition: Mitral Valve Stenosis, often seen in rheumatic fever, leading to increased heart workload and hypertrophy.

Septa within the Heart

  • Interventricular Septum:

    • Separates the right and left ventricles; contains the Bundle of His.

  • Interatrial Septum:

    • Contains the AV node (nerve fibers).

  • Pectinate Muscles: Muscular ridges found in the atria, increase the force of contraction.

  • Trabeculae Carneae: Ridges in ventricles that prevent wall sticking during contraction.

Coronary Circulation

  • Refers to the blood supply to the heart muscle itself, via coronary arteries/veins.

  • Coronary Sinus: A large venous collection point for returning blood from the heart muscle.

Angina and Myocardial Infarction (Heart Attack)

  • Angina: Chest pain due to ischemia (insufficient blood flow to the heart).

  • Myocardial Infarction (MI):

    • Occurs when an atheroma (fat or blood clot) blocks a coronary artery, causing downstream tissue death.

    • Symptoms include left arm pain, chest pain, and a sensation described as an "elephant on the chest."

Structure of Cardiac Muscle (Cardiomyocytes)

  • Features:

    • Surrounded by glycogen (a sugar reserve), typically containing one nucleus, branched structure, striations, and intercalated discs.

    • Intercalated Discs:

    • Specialized connections between cardiomyocytes that help synchronize contractions.

  • Gap Junctions: Allow electrical activity to flow freely between heart cells.

Electrical Conduction of the Heart

  • Controlled by:

    • Sympathetic Nervous System: Increases heart rate and contraction force (positive ionotropic and chronotropic activity).

    • Parasympathetic Nervous System: Decreases heart rate (negative chronotropic activity via vagus nerve).

  • Pathway: SA Node → AV Node → AV Bundle (Bundle of His) → Bundle Branches and Purkinje Fibers.

SA Node (Sinoatrial Node)

  • Located in the right atrium, contains modified pacemaker cells that generate electrical impulses for sinus rhythm.

  • Normal sinus rhythm: 70-80 bpm.

  • Fires to prompt atrial contraction.

AV Node (Atrioventricular Node)

  • Positioned near the tricuspid valve, connects electrical signals from atria to ventricles, slowing conduction allowing for adequate ventricular filling.

AV Bundle (Atrioventricular Bundle) and Purkinje Fibers

  • Play crucial roles in conducting electrical impulses to ensure the synchronized contraction of the heart's ventricles.

Cardiomyocyte Action Potential in SA Node

  • Depolarization Phase:

    • Opening of sodium channels, thresholds reached leading to the peak of action potential; this reflects chronotropic activity.

  • Plateau Phase:

    • Opening of slower calcium channels, leading to release of more calcium from the sarcoplasmic reticulum, responsible for ionotropic activity (force of contraction).

  • Repolarization Phase:

    • Calciuim channel closure and potassium channel opening; potassium influx returns cell to resting potential, again demonstrating chronotropic activity.

Electrocardiogram (ECG or EKG)

  • Utilized to visualize the electrical activity of the heart and to check for arrhythmias.

  • Components:

    • P Wave: Represents atrial depolarization triggered by SA node.

    • QRS Complex: Indicates ventricular depolarization.

    • ST Segment: Corresponds to ventricular systole (contraction phase).

    • T Wave: Reflects ventricular repolarization (diastole).

Abnormal EKGs

  • Associated with:

    • Myocardial infarctions, electrolyte or hormonal imbalances, and abnormalities in conduction (e.g., dead cardiomyocytes).

  • Ventricular Fibrillation:

    • A life-threatening arrhythmia that requires defibrillation (electric shock) treatment, commonly associated with myocardial infarctions.

Phases of the Cardiac Cycle

  • Ventricular Filling (Diastole):

    • Ventricles expand, lowering pressure and allowing blood flow from atria through AV valves.

    • Atrial contraction occurs (P Wave, systole) providing more blood to the ventricle.

    • Ends with End Diastolic Volume in ventricles.

  • Isovolumetric Contraction (Systole):

    • Ventricles contract, but no blood is ejected; pressure builds up.

  • Ventricular Ejection (Systole):

    • Ventricular pressure exceeds that in the great vessels, semilunar valves open and blood is ejected.

  • Isovolumetric Relaxation (Diastole):

    • Semilunar and AV valves close; blood is not moving until ventricular pressure decreases enough to open AV valves, allowing atrial blood flow into ventricles.

Cardiac Output and Stroke Volume

  • Cardiac Output:

    • Amount of blood annually ejected from the heart.

    • Formula: extCardiacOutput=extHeartRateimesextStrokeVolumeext{Cardiac Output} = ext{Heart Rate} imes ext{Stroke Volume}

  • Increased during exercise.

  • Stroke Volume:

    • Amount of blood ejected by a ventricle per pump.

  • Inotropic Agents: Influence contraction force.

    • Hypocalcemia: Can cause weak/irregular heartbeats.

    • Hypercalcemia: Can lead to strong, prolonged contractions and even cardiac arrest during systole.

  • Heart Rate:

    • Number of heartbeats per minute.

  • Chronotropic Agents: Factors influencing heart rate.

  • Tachycardia: Heart rate exceeding 100 bpm (common during exercise).

  • Bradycardia: Heart rate below 60 bpm (common during sleep).

Chronotropic Effects

  • Baroreceptors:

    • Pressure receptors in the aorta and internal carotid arteries; detect changes in blood pressure.

  • Chemoreceptors:

    • Chemical receptors located in the aortic arch, carotid arteries, and medulla oblongata; respond to pH changes.

  • Electrolytes:

    • Potassium (K+): Irregular rhythms possible with hyperkalemia or hypokalemia, affecting rates (bradycardia or tachycardia).

Congestive Heart Failure (CHF)

  • Results from various conditions (e.g., hypertension, myocardial infarction).

  • Right-Sided CHF:

    • Right ventricle fails to pump blood to the lungs.

    • Symptoms: Liver enlargement, ascites (fluid accumulation in abdominal cavity), distended jugular veins, edema in fingers, ankles, and feet.

  • Left-Sided CHF:

    • Left ventricle fails to pump blood to the body.

    • Symptoms: Shortness of breath or feelings of suffocation due to pulmonary congestion.