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Cardiovascular Physiology
Dr. Noha Elsayed
Objectives
• Describe Blood flow from the heart (Pulmonary and
systemic).
• Define cardiac output (CO) and list its determinants.
• Describe the events that comprise one cardiac cycle.
The heart
 The heart is the central pump of the cardiovascular system
that drives blood through the blood vessels.
Diastole
Systole
A heart beat consists of a systole plus a diastole of cardiac
chambers.
 The heart of a normal adult male beats automatically and
regularly at a rate of 75 beats/minute during rest. The
normal range of heart rate is between 60 – 100.
Tachycardia.
Bradycardia.
The heart as a pump:
The heart is two pumps in series (i.e., the right and
left sides) that are connected by the pulmonary
and systemic circulations.
Blood flow from the heart
During ventricular systole, blood is pumped into the
circulation.
During diastole, the pumping of blood stops and the
ventricles get filled with blood.
In this way, the flow of blood from the ventricles into the
systemic and pulmonary circulations is an intermittent
pulsatile flow.
Systemic and pulmonary
circulations
Cardiac output
* Cardiac output is the blood flow generated by each
ventricle per minute.
* The cardiac output is equal; to the volume of blood
pumped by one ventricle per beat times the
number of beats per minute:
COP = SV . HR
Where COP = cardiac output, SV = stroke volume,
and HR = heart rate.
The stroke volume for each ventricle averages 70 ml of blood, and
a normal heart rate is approximately 70-75 beats/minute;
therefore, the cardiac output at rest is approximately 5 L/min.
The heart rate is under neural control. Cardiac sympathetic
efferent activity increases the heart rate, whereas
parasympathetic (vagal) efferent impulses decreases heart rate.
The stroke volume varies with the volume of blood in the ventricle
at the onset of contraction, changes in the force of ventricular
contraction, and the arterial pressure.
Cardiac Cycle
 Electrical Conduction Pathway
◦ Initiated by the Sino-Atrial node (SA node) which is myogenic at 60-100
action potentials/minute
◦ Depolarization is spread through the atria via gap junctions and
internodal pathways to the Atrio-Ventricular node (AV node)
 The fibrous connective tissue matrix of the heart prevents further spread of
APs to the ventricles
 A slight delay at the AV node occurs
 Due to slower formation of action potentials
 Allows further emptying of the atria
◦ Action potentials travel down the Atrioventricular bundle (Bundle of
His) which splits into left and right atrioventricular bundles (bundle
branches) and then into the conduction myofibers (Purkinje cells)
 Purkinje cells are larger in diameter & conduct impulse very rapidly
 Causes the cells at the apex to contract nearly simultaneously
 Good for ventricular ejection
Cardiac Cycle
 Cardiac Cycle is alternating periods of systole and diastole
 Systole = period of contraction
 Diastole = period of relaxation
Phases of the cardiac cycle
1.Isovolumetric Ventricular Contraction phase:(beginning of
systole)
 After the ventricles have filled by a trial contraction ,AV valves close as
the ventricles begin their contraction and intraventricualar pressure
increases.
 The semi lunar valves remain closed and this makes ventricle a closed
cavity.
 The volume in the ventricles remains unchanged throughout the
contraction ,hence the name isovolumetric.
 Closure of the AV valves in this phase causes the first heart sound.
Cardiac Cycle
Phases
2. Rapid Ventricular Ejection
 Intraventricular pressure overcomes aortic pressure
 Semilunar valves open
 Blood is ejected
3. Reduced ejection
The continued contraction of the ventricles pushes the remaining blood into the
blood vessels (aorta and pulmonary artery)slowly.
At the end of this phase the ventricles begin to relax.
4 .protodiastolic phase
When ventricles begin to relax ,the AV valves close and the semilunar valves
remain open.
As the intra ventricular pressure decreases below the pressure in the aorta and
pulmonary artery ,the blood tries to come back into the ventricles,
This is prevented by closure of semilunar valve which produces the second heart
sound.
5 . Isovolumetric Ventricular Relaxation(beginning of diastole)
 Intraventricular pressure drops below aortic pressure
 Semilunar valves close = second heart sound (dup)
 Pressure still hasn’t dropped enough to open AV valves so volume remains
same (isovolumetric)
• 6 .first rapid ventricular filling :
•
•
Since there is reduced intraventricualar pressure in this phase causing the
semilunar valves to close .
The AV valves open and there is sudden rush of blood into the ventricles from the
atria.
• 7 .reduced ventricular filling :
• During this phase both atria and ventricles are relaxing ,the blood entering
the atria ,fill the ventricles passively.
• 8 .last rapid filling phase:
• This phase coincides with a trial contraction.
• The atria are in systole forcing blood into the ventricles which are relaxed.
Cardiac Cycle
Phases
Task for home
• Student 1 define cardiac output (CO) and list
its determinants.
• Student 2 Describe the events that comprise
one cardiac cycle with diagram.
• Student 3 coronary artery disease.
Reference
http://www.fundamentalsofanatomy.com/mcqs/mc
qlist.asp