DD

Heart Anatomy & Physiology – Vocabulary Review

Inspirational Opening

  • “KEEP LOOKING UP… THAT’S THE SECRET OF LIFE.”
    • Serves as motivational backdrop for the lesson and reminds health-science students to maintain optimism during study and practice.

Anatomy vs. Physiology

  • Anatomy = structure
    • Example: Describe the heart’s appearance, size, and location.
  • Physiology = function
    • Example: Explain what the heart does (e.g., pumps blood).
  • Both perspectives are needed for a complete understanding of the cardiovascular system.

Heart Overview & Location

  • Muscular organ ≈ size of an adult man’s closed fist.
  • Functions to pump enough blood to meet metabolic demands.
  • Normal sinus rhythm (NSR) beats: 60\text{–}100\,\text{beats/min}.
  • Located in thoracic cavity:
    • In the mediastinum
    • Above diaphragm, behind sternum, in front of spine
    • Tilted leftward: broad top = base; narrow tip = apex.

Layers of the Heart Wall

  • Epicardium (Visceral pericardium)
    • Outermost; houses coronary arteries.
  • Myocardium
    • Middle, thickest layer, muscular; responsible for contraction/relaxation.
    • Site affected in myocardial infarction (MI = myocardial tissue death).
  • Endocardium
    • Innermost, thin; forms valves and harbors conduction system.

Medical Terminology Roots & Prefixes

  • \text{cardi} = heart
  • \text{pulmon}/\text{pneum} = lungs
  • \text{epi} = upon/outer
  • \text{endo} = inside/within
  • \text{my}/\text{myo} = muscle
  • \text{peri} = around/surrounding

Pericardium

  • Double-walled sac enveloping heart; provides support & protection.
  • Contains pericardial fluid between its layers to minimize friction during each heartbeat.
  • Layers (outside ➜ in):
    • Fibrous pericardium
    • Parietal pericardium
    • Pericardial cavity (fluid)
    • Visceral pericardium (= epicardium)

Heart Chambers

  • Heart divided by septa into left/right & upper/lower segments ➜ 4 chambers.
  • Atria (upper)
    • Right atrium: receives de-oxygenated blood from body.
    • Left atrium: receives oxygenated blood from lungs.
    • Smaller, thin-walled, low-pressure; deliver blood to ventricles.
  • Ventricles (lower)
    • Right ventricle: pumps blood to lungs for oxygenation.
    • Left ventricle: pumps oxygenated blood to entire body; has 3× muscle mass of right ventricle and generates highest pressures.

Heart Valves

  • Purpose: one-way flow, prevent backflow; opening/closing driven by pressure changes; closure produces heart sounds.
  • Atrioventricular (AV) Valves
    • Tricuspid (3 cusps) – between R atrium & R ventricle.
    • Bicuspid/Mitral (2 cusps) – between L atrium & L ventricle; disorder example: MVP (Mitral Valve Prolapse).
  • Semilunar Valves (half-moon shape)
    • Pulmonary valve – at R ventricle outflow ➜ lungs.
    • Aortic valve – at L ventricle outflow ➜ body.

Blood Vessels

  • Veins
    • Carry de-oxygenated blood toward heart (except pulmonary veins).
    • Largest: superior & inferior vena cava.
  • Arteries
    • Carry oxygenated blood away from heart (except pulmonary arteries).
    • Largest: aorta.
  • Capillaries
    • Microscopic vessels connecting arterioles to venules; site of nutrient/ O$_2$ exchange.

Blood Flow Through the Heart

\text{SVC/IVC} \to \text{R atrium} \to \text{tricuspid valve} \to \text{R ventricle} \to \text{pulmonic valve} \to \text{pulmonary artery} \to \text{lungs} \to \text{pulmonary veins} \to \text{L atrium} \to \text{mitral valve} \to \text{L ventricle} \to \text{aortic valve} \to \text{aorta} \to \text{body}

Cardiac Cycle

  • Diastole = ventricular relaxation & filling.
  • Systole = ventricular contraction & ejection.
  • One cardiac cycle = 1 systole + 1 diastole = 1 heartbeat/pulse.

Systemic Circulation Pathway

\text{Aorta} \to \text{arteries} \to \text{arterioles} \to \text{capillaries} \to \text{venules} \to \text{veins} \to \text{vena cava}

  • Oxygen & nutrients diffuse in capillary bed; de-oxygenated blood returns via veins.

Coronary Arteries (Heart’s Own Blood Supply)

  • Originate at aortic root; run superficially (epicardial) then dive into myocardium.
  • Perfuse primarily during diastole.
  • Main branches:
    • Left anterior descending (LAD) – anterior wall of L ventricle.
    • Circumflex – lateral wall of L ventricle; gives Posterior Descending Artery (PDA) in 30% of people.
    • Right coronary artery (RCA) – R ventricle & inferior L-ventricle; gives PDA in 70% of people.

Heart Cell Types

  • Contractile cells – generate mechanical pump action.
  • Conduction system cells – generate & propagate electrical impulses.

Autonomic Nervous Control

  • Controlled by Autonomic Nervous System (ANS):
    • Sympathetic – increases rate, conduction speed, contractility.
    • Parasympathetic – slows these parameters (via vagus nerve).

Cardiac Conduction System

  • Creates & distributes electrical impulses telling heart when to contract.
  • Relies on electrolytes \text{Na}^+, \text{K}^+, \text{Cl}^-; imbalances → arrhythmias.

Key Electrophysiologic Properties

  • Automaticity – generate impulse spontaneously.
  • Conductivity – pass impulse to neighboring cells.
  • Excitability – depolarize in response to stimulus.
  • Contractility – shorten muscle fibers (mechanical).

Conduction Pathway & Intrinsic Rates

  1. Sinoatrial (SA) node – natural pacemaker; location: upper R atrium; fires 60\text{–}100\,\text{bpm}.
  2. Atrioventricular (AV) node – backup pacemaker; lower R atrium; fires 40\text{–}60\,\text{bpm}.
  3. Bundle of His – septal tract; fires 40\text{–}60\,\text{bpm}.
  4. Bundle branches (R & L) – subdivision of His; same intrinsic rate.
  5. Purkinje fibers – penetrate ventricular myocardium; fires 20\text{–}40\,\text{bpm} and directly trigger ventricular contraction.

Conduction Variations & Clinical Implications

  • Normal impulse flow depends on integrity of each component; damage (e.g., ischemia, electrolyte disorder) forces alternate pacemakers to take over, altering heart rate/rhythm.
  • Understanding pathway is essential for ECG interpretation and arrhythmia management.

Multimedia & Further Study

  • Heart Valve Animation: https://www.youtube.com/watch?v=agePsMW5f5A
  • Anatomy Overview: https://www.youtube.com/watch?v=UMTDmP81mG4
  • Heart Function Animation: https://www.youtube.com/watch?v=3lrjBWhdZ6s
  • Conduction System Video: https://www.youtube.com/watch?v=RYZ4daFwMa8

Ethical & Practical Connections

  • MI (myocardial infarction) emphasizes importance of early intervention and patient education.
  • Valve disorders (e.g., MVP) illustrate preventive care and surgical decision-making.
  • Autonomic control insight guides pharmacologic therapies (beta-blockers, anticholinergics).
  • Accurate knowledge of conduction system is critical for defibrillation, pacemaker implantation, and advanced cardiac life support (ACLS).