Cardiac Anatomy & Physiology: Quick Review

Valves and Flow Direction

  • Atrioventricular valves (tricuspid on the right, mitral/bicuspid on the left) open downward toward the ventricles; attached to papillary muscles via chordae tendineae to prevent prolapse.

  • Semilunar valves open in the opposite direction (toward the vessels leaving the heart); ensure unidirectional flow; both valve types should only open in their designated direction.

Endocarditis and Dental Health

  • Bacteria from dental plaque can enter the bloodstream and colonize the endocardium/valves, causing endocarditis.

  • Poor dental health increases risk; maintain oral hygiene (brush, floss, and drink water after meals) to reduce bacteria load.

  • Water after meals can help wash away food particles and bacteria, correlating with lower endocarditis risk in some populations.

Intercalated Discs: Desmosomes and Gap Junctions

  • Intercalated discs contain desmosomes (mechanical coupling) and gap junctions (electrical coupling).

  • Arrangement: desmosome - gap junction - desmosome - gap junction.

  • Desmosomes prevent tearing during continuous contraction; gap junctions coordinate synchronized contraction.

Skeletal vs Cardiac Muscle Contraction: Key Differences

  • Skeletal muscle: contraction follows a latent period, contraction, and relaxation with rapid Ca^{2+} release.

  • Cardiac muscle: contraction features a strong, plateau phase; Ca^{2+} release is slower and more controlled, allowing a hold before relaxation.

  • Implication: cardiac contraction is sustained to move blood effectively and prevents tetany of the heart muscle.

Action Potentials and Contraction Timeline

  • Depolarization (sodium entry): extNa+ext{Na}^+ influx via voltage-gated channels; triggers contraction.

  • Repolarization: K+K^+ efflux returns the membrane toward baseline.

  • Na^{+}/K^{+} ATPase maintains ion gradients.

  • Timeline: latent period (AP onset) → contraction → relaxation; skeletal ! and cardiac timelines differ, with cardiac showing a pronounced plateau due to Ca^{2+} handling.

  • In skeletal muscle, contraction is tied to a quick Ca^{2+} release; in cardiac muscle, the calcium release is slower and contributes to the plateau.

Intrinsic Cardiac Conduction: Initiation and Coordination

  • Initiation begins in the right atrium (intrinsic pacemaker region) and is propagated to coordinate whole-heart contraction.

  • Proper sodium influx triggers the heartbeat; coordinated conduction ensures the entire heart contracts together.

  • If conduction is disrupted, the heart may not beat properly, affecting overall function.

  • Analogy reference: signaling and “sidings” help coordinate direction and timing to avoid mis-timed contractions.