Physiology of Excitatory and Conducting System of Heart by Dr. Mudassar Ali Roomi

7/28/2019 Physiology of Excitatory and Conducting System of Heart by Dr. Mudassar Ali Roomi

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HEART PHYSIOLOGY

RHYTHMICAL EXCITATION OF HEART

By

Dr. Mudassar Ali Roomi (M.B;B.S, M.PHIL.)


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CONDUCTION SYSTEM OF HEART

SA node

Internodal pathways

AV node

AV bundle of His

Right and left bundle

branches

Purkinje fibers


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Conduction System

of the Heart SA node: sinoatrial node. Thepacemaker.

Specialized cardiac muscle cells.

Generate spontaneous actionpotentials (autorhythmic tissue).

Action potentials pass to atrial musclecells and to the AV node


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Conduction System

of the Heart

AV node: atrioventricular node.

Action potentials conducted moreslowly here than in any other part of

system.

Function: Ensures ventricles receivesignal to contract after atria havecontracted


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Conduction System

of the Heart

AV bundle: passes through hole incardiac connective tissue skeleton

to reach interventricular septum


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Conduction System

of the Heart

Right and left bundle branches:extend beneath endocardium to

apices of right and left ventricles


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Conduction System

of the Heart

Purkinje fibers:

Large diameter cardiac muscle cells withfew myofibrils.

Many gap junctions.

Conduct action potential to ventricular

muscle cells (myocardium) very rapidly


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Rate of impulse generation in heart:

SA NODE: 70-80/min

AV NODE: 40-60/min

AV BUNDLE, BRANCHES & VENTRICLES: 15-40/min

SA NODEnormal PACEMAKER

OTHERS ECTOPIC FOCI


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AV Node, and Delay of Impulse Conduction from the

Atria to the Ventricles

Locationof the A-V node:in the posterior wall of theright atrium immediatelybehind the tricuspid valve

there is a delay of 0.09second in the A-V node

A delayof another 0.04second occurs mainly in A-Vbundle

Thus, the total delay in theA-V nodal and A-V bundlesystem is about 0.13second.


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AV Node, and Delay of Impulse Conduction

from the Atria to the Ventricles

Cause of the Slow Conduction:

caused mainly by decreasednumbers of gap junctionsb/w successive cells in the

conducting pathwaysImportance of AV nodal delay:

this delay allows time forthe atria to empty theirblood into the ventriclesbefore ventricularcontraction begins.


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Rapid Transmission in the

Ventricular

Purkinje System

They are very large fibers, even

larger than the normal

ventricular muscle fibers

and they transmit action

potentials at a velocity of 1.5 to

4.0 m/sec, a velocity about 6

times that in the usual

ventricular muscle and 150 timesthat in some of the A-V nodal

fibers.


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Ventricular

Purkinje SystemCause of rapid transmission:

The rapid transmission of actionpotentials by Purkinje fibers is

believed to be caused by a very

high level of permeability of the

gap junctions at the intercalated

discs between the successive

cells that make up the Purkinje

fibers.


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Ventricular

Purkinje SystemFUNCTION: rapid transmission in

Purkinje fibers is responsible for

synchronous contraction of

ventricular muscle.


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Conduction velocities of hearttissues:

ATRIAL MUSCLE= 0.3m/sec

INTERNODAL PATHWAYS=

1m/sec AV NODE: slowest 0.05-

0.1m/sec

AV BUNDLE &BRANCHES/PURKINJE SYSTEM:

Maximum velocity= 1.5-4m/sec

VENTRICULAR MUSCLE=0.5m/sec

SUMMARY OF SPREAD OF THE CARDIAC IMPULSE THROUGH

THE HERAT


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ECTOPIC PACEMAKER OF HEART

Normal pacemaker of

heart?

Ectopic pacemaker?

Causes of ectopicpacemaker of heart?

1. Excessive excitability of

some part of the heartother than SA node

2. Heart blocks

Physiology of Excitatory and Conducting System of Heart by Dr. Mudassar Ali Roomi

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