Study Notes

Anatomy, Physiology & Pathology Notes of the CARDIOVASCULAR SYSTEM Final Edition | PRE-SUMMARIZED READY-SUMMARIZED HIGH-YIELD NOTES For NURSING, MEDICAL, PRE-MED, USMLE OR PA STUDENT

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Study Notes
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1. Anatomy of the Heart
  • Layers of the Heart Wall:
    • Epicardium: Outer protective layer (visceral layer of serous pericardium).
    • Myocardium: Middle muscular layer; responsible for pumping. Thickest in the left ventricle.
    • Endocardium: Inner endothelial lining of heart chambers and valves.
  • Chambers & Blood Flow:
    • Right Atrium (RA): Receives deoxygenated blood via Superior/Inferior Vena Cava and Coronary Sinus.
    • Right Ventricle (RV): Pumps deoxygenated blood through the pulmonary valve into the pulmonary trunk/arteries.
    • Left Atrium (LA): Receives oxygenated blood via four pulmonary veins.
    • Left Ventricle (LV): Pumps oxygenated blood through the aortic valve into the aorta. (3x thicker muscle wall than RV).
  • Valves:
    • Atrioventricular (AV) Valves: Tricuspid (right) and Bicuspid/Mitral (left). Prevent backflow into atria during ventricular systole. Anchored by chordae tendineae and papillary muscles.
    • Semilunar (SL) Valves: Aortic and Pulmonary. Prevent backflow into ventricles during ventricular diastole.

2. Cardiac Physiology & Electrical Conduction
  • Conduction System Pathway:
    1. SA Node (Sinoatrial): Primary pacemaker (60–100 bpm). Located in the upper right atrium.
    2. AV Node (Atrioventricular): Delays impulse (~0.1 sec) to allow atrial contraction/filling (40–60 bpm).
    3. Bundle of His (Atrioventricular Bundle): Transmits signal down interventricular septum.
    4. Right & Left Bundle Branches: Conduct impulses toward apex.
    5. Purkinje Fibers: Rapidly spread impulse through ventricular myocardium (20–40 bpm).
  • The Cardiac Cycle (Wiggers Diagram Basics):
    • Systole: Contraction phase (isovolumetric contraction + ventricular ejection).
    • Diastole: Relaxation phase (isovolumetric relaxation + ventricular filling).
    • S1 ("Lub"): Closure of AV valves (mitral/tricuspid) at the start of systole.
    • S2 ("Dub"): Closure of SL valves (aortic/pulmonic) at the end of systole.
  • Hemodynamic Formulas:
    • Cardiac Output (CO): CO = HR × SV (Normal: ~5 L/min).
    • Stroke Volume (SV): End-Diastolic Volume (EDV) minus End-Systolic Volume (ESV). Determined by:
      • Preload: Degree of myocardial stretch before contraction (venous return).
      • Afterload: Resistance the ventricle must overcome to eject blood (aortic pressure/SVR).
      • Contractility: Inotropy; intrinsic strength of cardiac muscle.
    • Mean Arterial Pressure (MAP): \(\text{MAP} = \text{DBP} + \frac{1}{3}(\text{SBP} - \text{DBP})\) or CO × SVR.

3. Vascular Physiology & Blood Pressure
  • Vessel Types:
    • Elastic Arteries (Aorta): Windkessel effect; smooth out pressure surges.
    • Muscular/Distribution Arteries: Adjust blood flow via vasoconstriction/vasodilation.
    • Arterioles: Resistance vessels; primary controllers of systemic blood pressure.
    • Capillaries: Exchange sites (single layer of endothelial cells).
    • Veins/Venules: Capacitance vessels; hold ~64% of blood volume.
  • Regulation of Blood Pressure:
    • Baroreceptors: Carotid sinus and aortic arch detect stretch; send signals to medulla to adjust HR and vasomotor tone.
    • RAAS (Renin-Angiotensin-Aldosterone System): Low BP → Kidney releases renin → Angiotensinogen converted to Angiotensin I → ACE converts to Angiotensin II (potent vasoconstrictor) → Aldosterone release → Na⁺ and H₂O reabsorption.

4. Pathology & High-Yield Disease States
  • Ischemic Heart Disease (IHD):
    • Angina Pectoris: Transient chest pain without necrosis. Stable (predictable) vs. Unstable (unpredictable/crescendo).
    • Myocardial Infarction (MI): Necrosis of myocardial tissue due to prolonged ischemia.
      • STEMI (ST-elevation) vs. NSTEMI (non-ST elevation).
      • Biomarkers: Troponin I/T (rises in 2–4 hrs, peaks at 24 hrs, stays elevated 7–10 days) and CK-MB.
  • Heart Failure (HF):
    • Left-Sided HF: Backup into lungs. Symptoms: Dyspnea on exertion, orthopnea, paroxysmal nocturnal dyspnea, crackles, S3 gallop.
    • Right-Sided HF: Backup into systemic circulation. Symptoms: Jugular venous distension (JVD), peripheral pitting edema, hepatomegaly, ascites. (Most common cause is left-sided HF).
  • Valvular Disorders:
    • Aortic Stenosis: Obstruction of LV outflow. Causes systolic ejection murmur (crescendo-decrescendo). Classic triad: Syncope, Angina, Dyspnea (SAD).
    • Mitral Regurgitation: Backflow into LA during systole. Causes holosystolic/pansystolic murmur radiating to the axilla.
  • Hypertension (HTN) & Vascular Pathology:
    • Essential vs. Secondary HTN: Essential is idiopathic (90%); secondary has an identifiable cause (e.g., renal artery stenosis).
    • Atherosclerosis: Accumulation of lipid-rich plaques in the intima of large/medium arteries → risk of rupture, thrombosis, aneurysm.

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