Download Heart 2 PPT

Collin County Community College
BIOL. 2402
Anatomy & Physiology
WEEK 5
The Heart
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The Heart Beat and the EKG
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The Heart Beat and the EKG
P-wave
= Atrial depolarization
QRS-wave
= Ventricular depolarization
T-wave
= Ventricular repolarization
PR-interval
= time for signal to go from
SA node to AV node
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The Heart Beat and the EKG
• SA node sets the rhythm.
• if SA nodes becomes damaged, AV node will take over in
setting the rhythm, but at a lower pace
• If AV node is damaged, Bundle of His sets the rhythm.
However, that rhythm is too slow to be compatible with life
• Ectopic foci
• Abnormal conducting or contractile cells that generate
AP’s and override the impulse rhythm of SA or AV node
• Regular sinus rhythm : no rhythmic disturbances
• Sinus tachychardia : increased rhythm ( HR > 100/min)
• Sinus tachychardia : decreased rhythm ( HR < 50/min)
• Sinus arrhythmia : HR fluctuates in synchrony with respiration
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The Heart Beat and the EKG
Abnormal patterns
• large QRS wave may indicate an enlarged heart
• small T wave may indicate coronary ischemia or ion imbalances
• increased PR interval may indicate atrial scarring
• increased QT interval may indicate ventricular conduction problems
• First degree heart (AV) block
• increased PR interval
• Second degree heart (AV) block
• not every P wave is followed by a QRS wave
• Third degree heart (AV) block
• atria and ventricles beat independently
• Ventricular fibrillation
• No coherent contraction of the myocadrial muscle mass
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3
Normal
ECG: P waves (atrial depolarization) are followed faithfully by
QRS (ventricular depolarization) and T waves (ventricular repolarization).
1st degree heart block
ECG: PR segment is longer than normal
2nd degree heart block
ECG: every other P wave fails to evoke QRST (partial atrioventricular block).
3rd degree heartblock
ECG: P waves and QRST occur independently (full atrioventricular block).
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The Heart Beat and the EKG
The action potentials of the autorhythmic cells is passed on to the
contractile cells where it starts the process of contraction.
Since heart cells are connected via gap junctions, a wave of
depolarization and contraction will be passed on from cell to cell.
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4
The ECG and Heart Muscle Cells AP’s
The relationship between
the electrocardiogram
(ECG), recorded as the
difference between currents
at the left and right wrists,
Note the much smaller scale for the ECG potential.
and
an action potential typical
of ventricular myocardial
cells.
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Heart Muscle Cell AP and Contraction
Heart muscle tension development starts right after the
initiation of the myocardial action potential refractory
Compared to skeletal muscles, cardiac muscles have a prolonged
refractory period. ( a few msecs compared to 250 msec)
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5
Heart Muscle Cell AP and Contraction
The prolonged refractory period of cardiac muscle
prevents tetanus contractions and is due to the opening of Ltype Calcium channels. It allows the heart to relax and fill with
blood again before the next contraction.
Opening of the L-type Calcium channels provides the
prolonged depolarization plateau, due to an influx of Calcium
in to the myocardial cells.
This influx of calcium is not only important for the prolonged
depolarization of the myocardial cell but it is also important
because it induces the release of Calcium from the SR.
Without this influx, calcium can not be released from the SR
and contraction is not possible.
This event is referred to as Calcium - induced Calcium release
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Heart Muscle Cell AP and Contraction
Time when calcium induced calcium release starts
Time when tension development (contraction) starts
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Calcium induced contraction
events in cardiac cells.
Relaxation in heart muscle
cells occurs when:
• Calcium is pumped
back into SR by means
of Ca-ATPase pumps
• Calcium is pumped out
of the cell by means of
Na-Ca antiports via a
secondary active
transport mechanism.14
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Heart Muscle Cell AP and Contraction
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The Cardiac Cycle
During a cardiac cycle, the heart goes through a sequence of phases
The systolic phase
= contraction phase
The diastolic phase
= relaxation phase
A normal cycle
• starts when both atria and ventricles are in a relaxed state
• the two atria contract first while the ventricles relax
• the atria then relax while the ventricles contract
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8
The Cardiac Cycle
The cardiac cycle can be divided into 3 specific Periods
The Ventricular Filling period
The Isovolumetric Contraction period
The Ejection period
The Isovolumetric Relaxation period
Atrial Systole
Ventricular Systole
Ventricular Diastole
Since it is a cycle , we can ‘look’ at this cycle from any point
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The Cardiac Cycle
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9
Atrial Systole : = ventricular filling
• pressure inside Ventricles
drops and opens AV valve
• blood flows in ventricles
and volume content of
ventricle increases (pressure
increases very slowly)
• ~ 80% of ventricular blood
content is purely by pressure
differential influx
• SA node fires and atria
contract, forcing last 20% of
blood into ventricles
AV valve
End of this period occurs when
atria relax and electrical
impulse reaches AV node
SL valve
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Ventricular Systole
• starts when AV node passes
impulse on to bundle of His
• ventricles contract and pressure in
ventricles increases dramatically
• immediately pushes the AV
valves to close
• both AV and SL valves are closed
now
• = iso volumetric contraction
contraction
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Ventricular Systole
• starts when pressure in this closed
system becomes higher than aortic
pressure
• pushes the SL valve open and blood is
ejected into the aorta
= ventricular ejection
• end point is reached when ventricles
start to relax, ventricular pressure falls
below aortic pressure and SL-valves shut
close
AV valve
SL valve
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Ventricular Diastole
• starts with the T-wave
The Relaxation
Period
• both atria and ventricles are relaxed
• blood pressure in aorta closes the SL-valve
• the AV-valve is still closed
• lack of contraction causes pressure to drop
in ventricle and atria
• blood returns from vena cava into atria
• since both SL and AV valves are closed
this period is referred to as Iso-Volumetric
Relaxation period
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The Cardiac Cycle
Systole:
ventricles contracting
Diastole:
ventricles relaxed
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The Cardiac Cycle
Pressure and volume
changes in the left heart
during a contraction cycle.
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Pressure and volume changes
in the left heart during a
contraction cycle.
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The Cardiac Cycle and Heart sounds
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13
The Cardiac Cycle and Heart sounds
• Auscultation – listening to heart sound via
stethoscope
• Four heart sounds
– S1 – “lubb” caused by the closing of the AV valves
– S2 – “dupp” caused by the closing of the semilunar
valves
– S3 – a faint sound associated with blood flowing into
the ventricles
– S4 – another faint sound associated with atrial
contraction
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The Cardiac Cycle
Heart beats on average 75 beats per minute
That is 0.8 seconds per beat
Time
Atria
Ventricles AV-valves SL-valves
0.4 sec DiaSt
DiaSt
Open
Closed
0.1 sec Syst
Diast
Open
Closed
0.3 sec DiaSt
Syst
Closed Open
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The Cardiac Cycle
Amount of blood in ventricles at end of Diastole = End-Diastolic
Volume ( is maximum filling)
Amount of blood left in ventricles at end of Systole = EndSystolic Volume ( what remains after ejection)
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The Cardiac Cycle and Stroke Volume
Stroke Volume = Volume ejected by a ventricle per beat
= End Diastolic minus End Systolic Volume
SV = EDV - ESV
SV = 135 ml - 65 ml = 70 ml
In a healthy heart, output of the right side must
equal that of the left side !
Left Ventricular SV =
Right Ventricular SV
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The Cardiac Cycle and Stroke Volume
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The Cardiac Cycle and Cardiac Output
Cardiac Output
= Blood Volume ejected by a ventricle per minute
= Blood Volume that goes into circulation per minute
= Blood Volume ejected per beat times beats per minute
Cardiac Output = SV x HR
= 75 ml x 70 beats/min
= 5,250 ml /min
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Cardiac Output and Energy Demand
The blood only holds a certain amount of oxygen
During exercise, the body and tissues need more oxygen
and nutrients to generate the required ATP
The only way to increase the oxygen supply is to increase
the blood supply = increase cardiac output
Cardiac Output = SV x HR
• increase Stroke Volume
• increase Heart Rate
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