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Dr. Foadoddini ١
Heart Muscle; The Heart as a Pump and Function of the Heart Valve
The HeartChapt. 9
By: Dr. FoadoddiniDepartment of Physiology & PharmacologyBirjand University of Medical Sciences
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Electrical Activity of the Heart
•
Ion channels:
–
They are selective
–
A given ion may have several
different channel
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Excitation-contraction coupling
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Electrical Activity of the Heart
•
Maintenance of Ionic
Gradient:–
Digitalis inhibit Na‐K pump
–
[Ca]o
= 2×10‐3 and [Ca]i
= 10‐7
–
10‐5 M
–
Na‐Ca Exchanger can operate in either
direction (depend upon the membrane
potential)
–
Decreased Na‐K ATPase
activity
increase intracellular Na and Ca
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Intercalated disckFunctional Syncytium
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Electrical Activity of the Heart
•
Action potential:
The long ERP prevent the heart developing sustained, tetanic
contractionThese potentials are so called ‘Fast Response’ action potential because of rapid phase 0 depolarization
↑IK
(Delayed rectifier)
↓IK
(Inward rectifier) I to
In non-pacemaker cells
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Cardiac valves
One way pathPassive opening/closing
Diameter diffferencesCordae
tendineae
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Volume-pressure curves as heart work
Area under curve as cardiac external work
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Cardiac cycle Pressure‐volume relationship
1.
ABC:
Ventricular Diastole
2.
CD:
Isovolumic
contraction.
3.
DF:
Ventricular Systole
4.
DE:
Ejection (Rapid and reduced
ejection)5.
FA:
Isovolumic
relaxation
6.
ABC:
Filling phase (Rapid filling
and diastases)Atrial
systole
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End-diastolic pressureVenous return/Atrial pressure CO
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Arterial pressure
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Rhythmical Excitationof the Heart
Chapt. 10
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Electrical Activity of the Heart
•
Action potential: In pacemaker cells
–
They are in SA and AV node
–
They do not have a true resting potential
–
Fast Na channels are inactivated
–
They induces Overdrive suppression
↑IK
(Delayed rectifier)
T-type Ca current
•These potentials are so called ‘Slow Response’ action potential because of slow phase 0 depolarization
•Sometimes Fast Responses are converted to the Slow Responses
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Stokes-Aadams syndrome (after A-V block)
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Electrical Activity of the Heart
•
At resting heart, vagal
influences are dominant over sympathetic (vagal
tone)
•
Change in heart rate = Chronotropy
•
Change in contraction = Inotropy
•
Change in conduction velocity
= Dromotropy
Neuronal mechanisms thatalter pace-maker activity
Normal range = 100 to 110 beats/min60 beats/min to over 200 beats/min
Ventricular escape
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