Home page Test Yourself

Physiology of the Circulatory System and the Use of Inotropes to Support Sick Children

 

Professional Development The Cardiovascular System Anatomy Physiology Pharmacology Paediatric Intensive Care        
 

Objectives:

The Electrical Activity of the Heart

v      Resting membrane potential

v      Cardiac Action Potential

v      Excitation-contraction coupling

v       Automaticity and the Electrical Conduction Pathway

v     Firing Rate of the Sinoatrial Node and Conduction Velocity 

Cardiac Function

v       The Cardiac Cycle

v       The Relationship between Cardiac Output, Heart Rate and Stroke Volume

v       Factors Affecting Heart Rate

v       Factors Affecting Stroke Volume

v       Determinants of End Diastolic Volume

v       Determinants of End Systolic Volume

Neurohormonal Regulation of the Heart

v       Receptors of the Heart and effect upon stimulation

v       Neural regulation involving the Autonomic Nervous System

v       Hormonal influences of Cardiac Function

v       Chemorecepors, Stretch Receptors and the Respiratory Reflex

Physiology and Regulation of the Circulatory System

v       Vasoconstriction, Vasodilatation and Vascular Tone

v       Haemodynamics

v       Mean arterial blood pressure

v       Central Venous Pressure

v       Autonomic Control of the circulation

v       Hormonal Control of the Circulation

v       Intrinsic Mechanisms of Circulatory Control

Vascular Reflexes

v       Baroreceptor Reflex

v       Chemoreceptor Reflex

v       The Renin-Angiotensin-Aldosterone System

v       Atrial Natriuretic Peptide and Vasopressin

Physiology

The Electrical Activity of the Heart

5.    Firing Rate of the Sinoatrial Node and conduction velocity

Learning Objective: To know the  factors influencing the firing rate of the sinoatrial node and conduction velocity within the heart

Back

Factors that alter the firing rate of the sinoatrial node and conduction velocity through the heart are as follow:

 

Increasing

 

Decreasing

Sympathetic Stimulation 

 

Parasympathetic stimulation

Muscurinic Receptor antagonist 

 

Muscurinic receptor agonist

Beta adrenoreceptor agonist 

 

Beta-blockers

Circulating catecholamines 

 

Ischemia/ hypoxia

Hyperthyroidism

 

Sodium and calcium channel blockers 

Hyperthyroidism-mainly affects firing rate of sinoatrial node 

 

Hypothyroidism-mainly affects firing rate of sinoatrial node 

 

The heart rate is controlled by the sinoatrial node as it has the fastest intrinsic firing rate. If the pacemaker cells of the sinoatrial node fails to depolarise the cells of the atrioventricular node are also capable of spontaneous depolarisation and takes over as the pacemaker of the heart. when this occurs ventricular contraction occurs much more slowly (about 40 beats/min) and independently of atrial conduction

Under Normal circumstances the cells of the atrioventricular node are responsible for conduction between the atria and the ventricles. The velocity of conduction is also determined by the electrical resistance between the cells and the nature of the action potentials based on the availability of ions and their movement through the myocardial cell membrane

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Further Information: Electrical Activity of the Heart

  Cardiac Physiology Electrical Activity The Electrocardiogram Rhythm Disorders
Anne Oluwafayokemi Faboya

References

Quick Start Guide