Download MBBS Physiology Presentations 65 Properties of Cardiac Muscle Part 2 Lecture Notes

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Properties of Cardiac muscle

(Part 2)

Properties of the cardiac muscle:

I.

Excitability

I .

Rhythmicity

I I.

Conductivity

IV. Contractility
Disorders of conduction and spread of impulse

WPW (Wolf-Parkinson-White) syndrome

Ectopic pacemakers

Extrasystole and compensatory pause



Disorders of conduction and spread of impulse

Stannius ligatures in amphibian heart

First ligature

Second ligature


Disorders of conduction and spread of impulse

A- V blockage

Ventricular escape

Stoke Adam Syndrome

Contractility

Action potential

Increase in intracel ular calcium

Contraction

Excitation-contraction coupling

Atrial and ventricular myocytes can contract while pacemaker and conducting system do not

Action potential and contraction in ventricle myocyte
Excitation-Contraction Coupling

Mechanism by which AP causes myofibrils to contract

AP passes over cardiac ms membrane

AP spread to interior of cardiac ms along T tubules

opening of Ca2+ channels in sarcolema

Ca2+ diffuses down gradient into cell through T tubules

Opening of Ca2+-release channels in SR

Ca2+ binds to troponin & stimulates contraction

Excitation-Contraction Coupling

During Repolarization

At the end of plateau of cardiac AP

Ca2+ is rapidly & actively pumped out

via a Na+- Ca2+- exchanger

Cessation of the contraction


Excitation-Contraction Coupling and Relaxation of Cardiac

Muscle

Factors affecting myocardium

1. Cardiac innervation

2. Effect of ions concentration in ECF

3. Physical factors

4. Blood flow

5. Chemical factors (drugs)
? Chronotropic
? Ionotropic
? Bathmotropic
? Dromotropic

Factors affecting myocardium

1. Cardiac innervation

2. Effect of ions concentration in ECF

3. Physical factors

4. Blood flow

5. Chemical factors (drugs)
Factors affecting myocardium

6. Mechanical factors:

a. Al or none law
b. Staircase phenomenon
c. Starling's law of the heart

Starling's law of the heart

"Length-tension relationship"

`Within limits, the greater the initial length of the fiber,

the stronger wil be the force of its contraction;

However, overstretching the fiber as in heart failure its

power of contractility decreases'

i.e. within limits, the power of contraction is directly

proportional to the initial length of the ms

Cardiac ms accommodates itself (up to certain limit) to

the changes in venous return


Pressure-volume loop