Download REGULATION OF HEART PUMPING

REGULATION MEANS
 Intrinsic cardiac regulation of pumping in response to changes in volume
of blood flowing into the heart.
 Autonomic nervous System by controlling heart rate and strength of heart
pumping.
INTRINSIC REGULATION (THE FRANK- STARLING
MECHANISM)
 Amount of blood pumping by the heart is determined by rate of blood
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flow in the heart by veins (venous return.)
The intrinsic ability of heart to adapt to increasing volume of inflowing
blood is called Frank-Starling mechanism of heart.
FSM means that the greater the heart muscle is stretched during filling
,the greater is force of contraction and greater the quantity of blood
pumped in aorta.
With in physiological limits the heart pumps all the blood that returns to
it by the way of vaina cava
.
EXPLANATION OF FRANK-STARLING
 When extra amount of blood flows into ventricles ,cardiac muscle its gets
stretched to greater length, this causes actin and myosin to overlap for
force generation.
 Therefore, the ventricle ,because of its increased pumping ,automatically
pumps the extra blood in to the arteries.
 The ability of stretching up to an optimal length is characteristic of all
striated muscles.
 Stretch of the right atrial wall directly increases the heart rate by 10 to 20
percent.
CONTROL BY SYMPATHETIC AND
PARASYMPATHETIC NERVES
 For given level of input atrial pressures ,the amount of blood pumped
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each minute (cardiac output)often can be increased by more than 100
percent by sympathetic stimulation.
The output can be decreased to as low as zero to almost zero by vagal
(parasympathetic)stimulation.
(Mechanism of excitation of heart by sympathetic nerves)
Strong sympathetic stimulation can increase heart rate from normal
70beats per minute upto 180 to 200 or sometime 250times per minute.
Heart contraction force increases to double than the normal.
Cardiac output increased twice.
PARASYMPATHETIC OR VAGAL STIMULATION.
 Strong stimulation of parasympathetic nerve fibres in the vagus nerve to
heart can stop heart beat for few seconds but than the heart usually
escapes and beats at a rate of 20 to 40 b/min as long as parasympathetic
stimulation.
 Heart muscle contraction strength decreased by 20 to 30 percent.
 Vagal fibres are distributed mainly to the atrias so it decreases heart rate
more than the strength of heart contraction.
 Great decrease in heart rate combined with slight decrease in contraction
strength can decrease ventricular pumping 50 percent or more.
EFFECT OF POTASSIUM AND CALCIUM IONS ON
HEART FUNCTION
 Effect of potassium ions: Excess potassium in the ECF causes heart to
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become dilated and flaccid and slows the heart rate.
Large quantities also can block conduction from the atria to ventricles.
Elevation of potassium level from 8 to 12mEq/L can cause weakness of
heart and abnormal rythm can cause death.
Effect of calcium ions:Excess of calcium ions causes heart to go in
spastic contraction.
Defeciency of calcium ions causes cardiac flaccidity similar to effect in
high potassium.
EFFECT OF TEMPERATURE ON HEART
FUNCTION
 Increased body temperature e.g fever causes a greatly increased heart rate
sometime as fast as double.
 Decreased temperature causes greatly decreased heart rate falling to as
low as few beats per minute.
The Heart: Conduction System
 The heart pumps blood through the body
 This is accomplished by contraction and relaxation of the cardiac muscle
tissue in the myocardium layer.
 Intercalated discs allow impulses to travel rapidly between adjacent cells so
they function as one rather than individual cells
Cardiac Muscle Tissue
intercalated disc
intercalated disc
Conduction System Continued….
 Cardiac conduction system: The electrical conduction system controls the
heart rate
 This system creates the electrical impulses and sends them throughout
the heart. These impulses make the heart contract and pump blood.
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Components of the Conduction System
 Sinoatrial Node
 located in back wall of the right atrium near the entrance of vena cava
 initiates impulses 70-80 times per minute without any nerve stimulation from
brain
 establishes basic rhythm of the heartbeat
 called the pacemaker of the heart
 impulses move through atria causing the two atria to contract.
 at the same time, impulses reach the second part of the conduction system
Components of the Conduction System Continued ….
 Atrioventricular Node :
 located in the bottom of the right atrium near the septum
 cells in the AV node conduct impulses more slowly, so there is a delay as
impulses travel through the node
 this allows time for atria to finish contraction before ventricles begin
contracting
Atrioventricular Bundle
 . “Bundle of His”
 From the AV node, impulses travel
through to the right and left bundle
branches
 These branches extend to the right
and left sides of the septum and
bottom of the heart.
Atrioventricular Bundle Continued….
 These branch a lot to form the Purkinje
fibers that transmit the impulses to the
myocardium (muscle tissue)
 The bundle of His, bundle branches
and Purkinje fibers transmit quickly
and cause both ventricles to contract at
the same time
 Like a “phone tree”
Atrioventricular Bundle Continued….
 As the ventricles contract, blood is forced out through the semilunar
valves into the pulmonary trunk and the aorta.
 After the ventricles complete their contraction phase, they relax and the
SA node initiates another impulse to start another cardiac cycle.
1 - Sinoatrial node (SA node)
2 - Atrioventricular node (AV node)
3 – Bundle of His
4 - Right & Left Bundle Branches
which lead to Purkinje Fibers