The Cardiac Cycle

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The Cardiac Cycle
• Refers to the events of 1 complete heart
beat
– Both atria & ventricles contract then relax
(0.8 sec if beating 75x/min)
• Key terms to know
– Diastole- relaxation
– Systole- contraction
– Lub-dub- the sound created by the closing of
the heart valves (AV and semilunar)
Filling Heart Chambers: Cardiac Cycle
Left atrium
Right atrium
Left ventricle
Right ventricle
Ventricular
filling
Mid-to-late diastole
(ventricular filling)
Figure 11.7, step 1a
Filling Heart Chambers: Cardiac Cycle
Left atrium
Right atrium
Left ventricle
Right ventricle
Ventricular
filling
Atrial
contraction
Mid-to-late diastole
(ventricular filling)
Mid-to-late diastole— blood flows from the atria into the
ventricles (both chambers are relaxed, AV valves open) then
the atria contract to squeeze remaining blood into the
ventricles
Filling Heart Chambers: Cardiac Cycle
Left atrium
Right atrium
Left ventricle
Right ventricle
Ventricular
filling
Atrial
contraction
Mid-to-late diastole
(ventricular filling)
Isovolumetric
contraction phase
Ventricular systole
(atria in diastole)
Filling Heart Chambers: Cardiac Cycle
Left atrium
Right atrium
Left ventricle
Right ventricle
Ventricular
filling
Atrial
contraction
Mid-to-late diastole
(ventricular filling)
Isovolumetric
Ventricular
contraction phase ejection phase
Ventricular systole
(atria in diastole)
Ventricular systole— blood pressure builds before ventricles
contract, when ventricles begin to contract pressure gets high
enough opening the semilunar valves allowing blood to be
pushed out to the lungs and body
Filling Heart Chambers: Cardiac Cycle
Left atrium
Right atrium
Left ventricle
Right ventricle
Ventricular
filling
Atrial
contraction
Mid-to-late diastole
(ventricular filling)
Isovolumetric
Ventricular
contraction phase ejection phase
Isovolumetric
relaxation
Ventricular systole
(atria in diastole)
Early diastole
Early diastole— atria finish refilling, when the pressure in the
atria exceeds the pressure in the ventricles the AV valves will
open allowing blood to fill the ventricles  the cycle begins
again
Murmur- condition in which one of the valves is
not functioning properly (could be an AV or
semilunar valves) and blood can flow
backwards/inefficiently through the heart.
Which phase of the cardiac cycle does this
picture show? How can you be sure?
Factors that Affect CO
1. Venous return (amount of blood that
enters the heart)
–Inc. venous return  inc. stretching
2. How much the ventricle is stretched prior
to contraction
–Inc. stretching inc. force of
contraction
3. High blood pressure
Factors that Change Heart Rate
• Crisis stressors
– Electrical system of the heart is more strongly
stimulated to beat  inc heart rate
• Congestive heart failure
– Heart “worn out”
– digitalis (drug) prescribed, strengthens
contractions to inc. cardiac output
• Epinephrine & thyroxine increase heart rate
• Electrolyte levels (ions)
– Low calcium depresses heart; high calcium causes
sustained contraction  can cause cardiac arrest
– Low potassium  irregular heartbeat
Physical Factors that
Affect Heart Rate
• Age – HR decreases with age
(healthy)
• Gender – Females > males
• Exercise – increases HR
• Body temp – higher temp
increases HR
The Cardiac Cycle
• Refers to the events of 1 complete heart
beat
– Both atria & ventricles contract then relax
(0.8 sec if beating 75x/min)
• Key terms to know
– Diastole- relaxation
– Systole- contraction
– Lub-dub- the sound created by the closing of
the heart valves (AV and semilunar)
Filling Heart Chambers: Cardiac Cycle
Left atrium
Right atrium
Left ventricle
Right ventricle
Ventricular
filling
Mid-to-late diastole
(ventricular filling)
Figure 11.7, step 1a
Filling Heart Chambers: Cardiac Cycle
Left atrium
Right atrium
Left ventricle
Right ventricle
Ventricular
filling
Atrial
contraction
Mid-to-late diastole
(ventricular filling)
Mid-to-late diastole— blood flows from the atria into the
ventricles (both chambers are relaxed, AV valves open) then
the atria contract to squeeze remaining blood into the
ventricles
Why?
Filling Heart Chambers: Cardiac Cycle
Left atrium
Right atrium
Left ventricle
Right ventricle
Ventricular
filling
Atrial
contraction
Mid-to-late diastole
(ventricular filling)
Isovolumetric
contraction phase
Ventricular systole
(atria in diastole)
Filling Heart Chambers: Cardiac Cycle
Left atrium
Right atrium
Left ventricle
Right ventricle
Ventricular
filling
Atrial
contraction
Mid-to-late diastole
(ventricular filling)
Isovolumetric
Ventricular
contraction phase ejection phase
Ventricular systole
(atria in diastole)
Ventricular systole— blood pressure builds before ventricles
contract, when ventricles begin to contract pressure gets high
enough opening the semilunar valves allowing blood to be
pushed out to the lungs and body
https://www.youtube.com/watch?v=rguztY8aqpk
Filling Heart Chambers: Cardiac Cycle
Left atrium
Right atrium
Left ventricle
Right ventricle
Ventricular
filling
Atrial
contraction
Mid-to-late diastole
(ventricular filling)
Isovolumetric
Ventricular
contraction phase ejection phase
Isovolumetric
relaxation
Ventricular systole
(atria in diastole)
Early diastole
Early diastole— atria finish refilling, when the pressure in the
atria exceeds the pressure in the ventricles the AV valves will
open allowing blood to fill the ventricles  the cycle begins
again
Think about it…
• What do you suspect happens to the
coronary blood vessels as the heart goes
through the cardiac cycle?
– What would happen to them during
systole?
– What would happen to them during
diastole?
Coronary Blood Vessels
• Feed the cardiac muscle
with oxygen rich blood
• The coronary vessels
branch off of the base
of the aorta
• Only fill with blood
when the pressure
inside of the aorta is
low and the blood flows
back towards the heart
https://www.youtube.com/watch?v=tBQa8IBzP6I&feature=related
What happens to a heart if it can’t get
enough oxygen?
HEART
ATTACK
Why?
http://www.youtube.com/watch?v=DGxS44-rcps
https://www.youtube.com/watch?v=eTKICIpShaA&feature=related
Factors that Affect CO
1. Venous return (amount of blood that
enters the heart)
–Inc. venous return  inc. stretching
2. How much the ventricle is stretched prior
to contraction
–Inc. stretching inc. force of
contraction
3. High blood pressure
Factors that Change Heart Rate
• Crisis stressors
– Electrical system of the heart is more strongly
stimulated to beat  inc heart rate
• Congestive heart failure
– Heart “worn out”
– digitalis (drug) prescribed, strengthens
contractions to inc. cardiac output
• Epinephrine increase heart rate
• Electrolyte levels (ions)
– Low calcium depresses heart, high calcium can cause
sustained contraction leading to cardiac arrest
– Low potassium causes irregular heartbeat
Physical Factors that
Affect Heart Rate
• Age – HR decreases with age
(healthy)
• Gender – Females > males
• Exercise – increases HR
• Body temp – higher temp
increases HR

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