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Phase 1 of the Cardiac Cycle
Ventricular filling (diastole)
1. Ventricles expand & AV valves open
2. Blood flows into ventricles quickly!, then
3. P-wave occurs
4. Atria contracts, sends last 1/3 of blood to
* At end of Phase 1:
each ventricle contains an end-diastolic
volume (EDV) of about 130mL
Phase 2 of the Cardiac Cycle
Isovolumetric Contraction (stystole)
1. QRS wave occurs
2. Atria repolarize & relax
3. Ventricles begin contracting
4. AV valves close
5. heart sound S1 occurs
6. Semilunar valves remain closed
7. No blood is expelled
Phase 3 of the Coronary Cycle
1. Semilunar Valves open
2. blood is ejected rapidly!, then slowly
3. each ventricle ejects a stroke volume of
about 70mL, which is an ejection fraction
of 54% of the EDV
4. blood remaining behind (60mL) is end-
systolic volume (ESV)
** T-wave begins @ middle of this phase
Phase 4 of the Cardiac Cycle
Isovolumetric Relaxation (diastole)
1. Ventricles repolarize & relax
2. Semilunar valves close
3. heart sound S2 occurs
4. AV valves remain closed
5. no blood enters ventricles until next
** each ventricle ejects same amount of
Pacemaker Physiology (PP)
1. Starts @ -60mV - showing depolarization
* caused by slow inflow of Na+ without out-
flow of K+
2. When Pacemaker Potential reaches
threshold of -40mV . . .
3. Voltage-regulated fast calcium channels
4. Ca2+ flows in from ECF - this produces
rising (depolarizing) phase of action
potential. (peaks slightly above 0 mV)
5. K+ gates open & K+ leaves cell (repolor-
6. K+ gates close & PP starts over again
** each depolarizaiton of SA node sets off
Electrocardiogram - P wave
P wave is produced when a:
* signal from the SA node spreads
through the atria and depolarizes them
** P wave indicates atrial depolarization
Electrocardiogram - QRS complex
* signal from the AV node spreads
through the ventricular myodardium
** QRS complex indicates ventricular
depolarization, BUT atrial repolarization
occurs at same time
Electrocardiogram - ST segment
* corresponds to the plateau in the myo-
cardial action potential & represents
the time when ventricles contract and
eject blood into the Aorta & Pulmonary
** Ventricular systole begins @ ST seg.
Electrocardiogram - T wave
T wave is:
* indicates ventricular repolarization and
is followed by ventricular diastole.
Pressure sensors found in the Aorta & internal Carotid Arteries.
* monitors blood pressure
Tension in the Ventricular Myocardium
immediately before it begins to contract.
** Amount of blood in left ventricle at end
of diastole = end-diastolic volume
Blood pressure in the Aorta & Pulmonary
Trunk immediately distal to the semilunar
* Amount of pressure left ventricle needs to open aortic valve
What are the 2 centers that con-
stitute the cardiac center?
1. Cardioacceleratory center
2. Cardioinhibitory center
* raises heart rate through sympathetic
* reduces heart rate through the para-
sympathetic fibers in the vagus nerve.
What does the Sympathetic and
Parasympatheic do to the heart?
They modify heart rate & contraction
If the time of Ventricular filling were
increased in duration
The end diastolic volume (EDV) would
When the Ventricles relax blood in
the Aorta flows ______
flows back toward the heart filling the
The small patch of heart tissue that depolorizes spontaneously to
begin each heartbeat is the
What chamber has to work harder than the others, so it has the thick-
The vessel just before the circum-
flex artery in normal circulation is
Anterior Interventricular artery
Arteries & Veins entering & leaving the
* Superior and inferior vena cava, pulmonary artery and vein, and aorta.
When the pacemaker potential
reaches threshold, what type of
channels open to allow Calcium and
Sodium to flow in from the ECF?
Voltage-regulated fast calcium-sodium
A pacemaker potential results from
A slow inflow of Na+ without a compensating
outflow of K+
The result of the cells of the SA node ex-
hibiting a potential in which the membrane
voltage starts at -60 mV and drifts spontan-
eously toward a threshold of -40 mV.
Fibers that relay the signal from the AV node to the ventricles, telling them to contract
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