O Coração como Bomba Vitalícia: Fisiologia do Músculo Cardíaco

The heart is a syncytium of cardiac muscle cells (cardiomyocytes) contracting ~100,000 times/day without fatigue.

Unique Features

• Striated but involuntary: Sarcomeres like skeletal muscle; autonomic control.
• Intercalated discs: Gap junctions (connexin-43) enable rapid electrical coupling; desmosomes resist mechanical stress.
• High mitochondrial density (30% volume): Obligate aerobic metabolism; uses fatty acids, lactate, glucose, ketones.
• Calcium-induced calcium release (CICR): AP → L-type Ca²⁺ channel → RyR2 → SR Ca²⁺ release → contraction.

Electrical Control

SA node (pacemaker) → atria → AV node (delay) → His-Purkinje → ventricles. Autonomic modulation: sympathetic ↑ rate/contractility; parasympathetic ↓ rate.

Workload Adaptation

Exercise → physiologic hypertrophy (↑ mass, normal geometry). Pressure/volume overload → pathologic remodeling (fibrosis, failure).

Continuous, autoregulated, and resilient — the heart exemplifies biologic engineering.