Post on 05-Apr-2018
transcript
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
1/16
April 18, 2012 1
BY
DR. MUDASSAR ALI ROOMI (MBBS, M.PHIL)
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
2/16
1-Automaticity and rhythmicity(autorhythmicity):
2:Conductivity
3-Contractility:
4-Excitability
5- All or none Law
6-Reractory period
April 18, 2012 2
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
3/16
Frank-Starling mechanism of the heartcotraction: greater the heart muscle isstretched during diastolic filling (more initial
or end diastolic length), the greater is the forceof contraction and the greater is the quantity ofblood pumped into the aorta(withinPhysiologic limits).
Frank starling Law is applied to eachindividual skeletal muscle fiber but on heart asa whole.
April 18, 2012 3
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
4/16
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
5/16
April 18, 2012 5
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
6/16
Excitability is the property to respond to stimuli.
Stimuli: nervous, chemical, mechanical, electrical.
This property enables the heart muscles to respondto artificial pacemaker.***
The Nerves, drugs, ions and ischemia affect the
excitability of cardiac muscles.
April 18, 2012 6
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
7/16
Each fiber contracts to its maximum or not atall in response to a threshold stimulus.
Obeyed by each skeletal muscle fiber
individually but by heart muscle as a wholebecause heart is a functional syncitium. ***
April 18, 2012 7
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
8/16
DEFINITION: it is the interval during which anormal cardiac impulse cannot re-excite analready excited area of cardiac muscle. (0.30-0.35
sec) Absolute refractory period: It is the period
during which already excited cardiac muscle doesnot respond to a second stimulus. (0.25-0.30 sec)**
Relative refractory period: It is the period duringwhich already excited cardiac muscle givesresponse to a powerful excitatory stimulus. (0.05
sec)**April 18, 2012 8
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
9/16
The normal refractory period of the ventricle isalmost equal to the duration of plateau phaseof action potential. ****
The refractory period of atrial muscle (0.15 sec)is much shorter than that of the ventricles (0.25
to 0.30 sec).
April 18, 2012 9
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
10/16
During relative refractoryperiod earlyprematurecontraction may occur
if heart is stimulated bya strong stimulus.
April 18, 2012 10
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
11/16
It is due to plateau inaction potential ofcardiac muscle
because plateauincreases therefractory period.
April 18, 2012 11
TETANIZATION SEEN INSKELETAL MUSCLE
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
12/16April 18, 2012 12
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
13/16
Ventricular Muscle Action Potential
-100
-80
-40
-60
+20
0
-20
2 3 40 1
MembranePotential
(mV
)
Seconds
Fast Na+
Channels Open
Slow Ca++
Channels Open
0
1
2
3
4
K+ Channels
Open
phase 0- Fast Na+ channels open then slow Ca++ channelsphase 1- K+ channels openphase 2- Ca++ channels open morephase 3- K+ channels open morephase 4- Resting membrane potential
K+ Channels
Open More
Ca++ Channels
Open More
Copyright 2006 by Elsevier, Inc.April 18, 2012 13
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
14/16
Resting membranepotential of the SAnodal fiber is -55 to -60mvolts.
The cause of this lessernegativity is that thecell membranes of thesinus fibers are
naturally leaky to Na+and Ca++ ions andentry of these ionsneutralize much of theintracellular negativity.
April 18, 2012 14
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
15/16
-100
-80
-40
-60
+20
0
-20
2 3 40 1
Seconds
Mem
branePotential(mV)
Threshold
Sinus Nodal
Fiber
Na+
Leak
Slow Ca++Channels Open
K+ Channels
Open more
Ventricular
Muscle fiber
Rhythmical Discharge of Sinus Nodal Fiber
April 18, 2012 15
8/2/2019 2nd Lecture on Heart Physiology by Dr. Roomi
16/16
At -55 mvolts, the fast Na+channels becomeinactivated.
Therefore, only the slowsodium-calcium channelscan open and cause theaction potential.
As a result, the SA nodal
action potential is slower todevelop than the that of theventricular muscle.
Therefore, the inherentleakiness of the sinusnodal
fibers to Na+ and Ca++ ionscauses their self
April 18, 2012 16