Chapter 3: Cardiovascular System — Heart, Vessels, and Blood

The cardiovascular system delivers oxygen and nutrients to every cell while removing metabolic waste. It is the most clinically critical organ system — cardiovascular disease remains the leading cause of death worldwide.

Cardiac Anatomy and the Cardiac Cycle

The heart has four chambers: two atria (receiving) and two ventricles (pumping). The right side handles pulmonary circulation; the left side drives systemic circulation. The heart wall has three layers: epicardium, myocardium, and endocardium.

Cardiac Conduction System:

1. SA node (sinoatrial) — the pacemaker, located in the right atrium (~60–100 bpm intrinsic rate)
2. AV node (atrioventricular) — delays the signal, protecting the ventricles
3. Bundle of His → Bundle Branches → Purkinje fibers — rapid ventricular depolarization

Cardiac Cycle:

• Systole — ventricular contraction, ejecting blood
• Diastole — ventricular relaxation and filling
• Normal cardiac output: ~5 L/min at rest (CO = HR × Stroke Volume)

Blood Pressure Regulation

Blood pressure (BP) = Cardiac Output × Peripheral Vascular Resistance. The renin-angiotensin-aldosterone system (RAAS) is the key long-term regulator:

• Low BP → kidney releases renin → angiotensin I → ACE converts to angiotensin II → vasoconstriction + aldosterone release → increased Na⁺/water retention → BP rises

Short-term regulation is mediated by the baroreceptor reflex in the aortic arch and carotid sinus.

Atherosclerosis and Coronary Artery Disease

Atherosclerosis is the buildup of lipid-laden plaques within arterial walls, driven by endothelial dysfunction, LDL oxidation, macrophage foam cell formation, and inflammation. Risk factors include hypertension, dyslipidemia, smoking, diabetes, and family history.

Myocardial infarction (MI):

• STEMI (ST-elevation MI): complete coronary occlusion — emergency reperfusion within 90 minutes (PCI preferred)
• NSTEMI (non-ST-elevation MI): partial occlusion — managed with anticoagulation and early catheterization

Diagnosis: troponin I/T (most sensitive and specific biomarker), ECG changes, clinical symptoms (chest pain radiating to left arm/jaw, diaphoresis).

Key Cardiovascular Drug Classes

Drug Class	Mechanism	Clinical Use
ACE inhibitors (e.g., lisinopril)	Block angiotensin II production	Hypertension, heart failure, post-MI
Beta-blockers (e.g., metoprolol)	Block β-adrenergic receptors	Hypertension, angina, arrhythmia, heart failure
Statins (e.g., atorvastatin)	Inhibit HMG-CoA reductase	Dyslipidemia, atherosclerosis prevention
Aspirin	Irreversible COX-1 inhibition → ↓TXA₂	Antiplatelet, acute MI, secondary prevention
Loop diuretics (furosemide)	Block Na⁺-K⁺-2Cl⁻ in loop of Henle	Heart failure, edema
Digoxin	Na⁺/K⁺-ATPase inhibitor	Atrial fibrillation, systolic heart failure

Key Checklist

• Traces the cardiac conduction pathway from SA node to Purkinje fibers
• Explains the RAAS mechanism and how ACE inhibitors interrupt it
• Distinguishes STEMI from NSTEMI and describes appropriate management