The Heart as the Central Pump of the Cardiovascular System
The Heart: Anatomy, Function & Role as the Cardiovascular Pump
The heart is a muscular pump that maintains continuous blood flow through ~60,000 miles of vessels. Understanding its structure explains how it serves as the cardiovascular system's engine.
Anatomical Overview
- Location: Mediastinum, left of midline, T5-T8 vertebrae
- Size: ~12 cm × 8 cm × 6 cm; 250-350g (clenched fist)
- Pericardium: Fibrous (protection) + serous (parietal/visceral + fluid)
- Wall layers: Epicardium (visceral pericardium), Myocardium (muscle), Endocardium (endothelium)
Four-Chamber Architecture
| Chamber | Receives | Pumps To | Wall Thickness | Pressure |
|---|
| Right atrium | SVC, IVC, coronary sinus | Right ventricle | Thin (2-3 mm) | Low (0-8 mmHg) |
| Right ventricle | Right atrium | Pulmonary artery | Moderate (3-5 mm) | 15-30 mmHg |
| Left atrium | 4 pulmonary veins | Left ventricle | Thin | Low (8-12 mmHg) |
| Left ventricle | Left atrium | Aorta (systemic) | Thick (10-15 mm) | 100-140 mmHg |
Valves: Unidirectional Flow
- AV valves: Tricuspid (R), Mitral (L) - prevent backflow to atria
- Semilunar valves: Pulmonic (R), Aortic (L) - prevent backflow to ventricles
- Chordae tendineae + papillary muscles: Prevent AV valve prolapse
Cardiac Cycle (One Heartbeat = 0.8 sec at 75 bpm)
- Atrial systole (0.1s): Atria contract → "atrial kick" (20-30% ventricular filling)
- Ventricular systole (0.3s):
- Isovolumetric contraction (valves closed, pressure ↑)
- Ejection (semilunar open, stroke volume ~70 mL)
- Ventricular diastole (0.4s):
- Isovolumetric relaxation
- Rapid filling (early)
- Diastasis (slow)
- Atrial systole (late)
Conduction System (Electrical Engine)
- SA node (60-100 bpm) - primary pacemaker
- AV node (40-60 bpm) - delay (0.12s) allows atrial kick
- Bundle of His → bundle branches → Purkinje fibers (20-40 bpm backup)
Coronary Circulation (Heart Feeds Itself)
- Right & left coronary arteries from aortic root
- Perfusion mainly during diastole (aortic pressure > ventricular)
- Autoregulation: metabolic demand → vasodilation (adenosine)
Cardiovascular Integration
- Systemic circuit: LV → aorta → arteries → capillaries → veins → RA (O₂ delivery)
- Pulmonary circuit: RV → PA → lungs → PV → LA (O₂ loading)
- Cardiac output: HR × SV = ~5 L/min at rest; ↑ 4-6x with exercise
Clinical Correlates
- Heart failure: pump failure (systolic) or filling failure (diastolic)
- Valvular disease: stenosis (obstruction) or regurgitation (backflow)
- Ischemia: supply-demand mismatch (coronary disease)
- Arrhythmias: conduction disruption
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