Understanding Heart Physiology and Function

Feb 3, 2025

Module 4 Lecture: Physiology of the Heart

Overview

  • Function of the Heart: Develops pressure to move fluid (blood) at an acceptable speed in a specific direction.
  • Cycle of Heart: Alternates between contraction (systole) and relaxation (diastole).

Heart Valves and Blood Flow

  • Atrioventricular Valves
    • Open when atrial pressure > ventricular pressure
    • Ensure one-way blood flow from atrium to ventricle.
  • Semilunar Valves
    • Open when ventricular pressure > arterial pressure
    • Ensure one-way blood flow from ventricle to arterial trunk.

Cardiac Cycle Mechanics

  • Proper heart function depends on timing of atrial and ventricular contraction.
  • Pacemaking and conduction systems provide necessary timing.

Cardiac Cells

  • Types of Cardiomyocytes
    • Nodal Cells (Pacemakers): Set the pace for heart contraction.
    • Contractile Cells: Perform contractions.

Nodal Cells (Pacemaker Cells)

  • Auto-rhythmicity: Ability to depolarize and start contractions without neural/hormonal stimulation.
  • Main locations:
    • SA Node: Top of right atrium.
    • AV Node: Near coronary sinus of interatrial septum, bottom of right atrium.

Electrical Signal Pathway

  • SA Node
    • Sends signals to both atria through internodal pathways.
    • Causes atria to contract, pushing blood into ventricles.
  • AV Node
    • Signal bottlenecks, pauses 0.1 seconds allowing ventricles to fill.
    • Travels through bundle of His to right/left bundle branches, then to Purkinje fibers.
  • Purkinje Fibers
    • Located at heart's apex.
    • Ensure bottom-up contraction for efficient blood expulsion.

Depolarization and Action Potentials

  • SA and AV Nodes
    • Spontaneously depolarize due to leaky channels.
  • Sodium-Potassium Pump
    • Maintains potential difference (negative inside cell).
  • Calcium Channels
    • Fast channels open at -40 mV, causing rapid depolarization.
  • Repolarization
    • Potassium exits, returning cells to resting state.

Summary

  • Alternation between depolarization and repolarization allows for continuous contraction and relaxation of cardiac tissue.
  • Next learning outcome will cover contractile cells.

Questions

  • If you have questions, contact via email.