Physiology of the
Cardiovascular System
Conduction System
SA Node
 Pacemaker
 Initiates the normal cardiac impulse
 Has intrinsic rhythm, initiates
impulses at regular intervals even
without stimulation by nerve impulses
 SA nodeinteratrial bundleleft
atrium contraction of atria
 SA node3 internodal
bundlesAV node
AV node
 Impulse passes slowly thru AV node
then speed up thru the AV bundle &
Purkinje fibers causing ventricles to
contract
Ectopic pacemaker
 If SA node loses its ability to generate
impulse, another portion of
conduction system can generate
impulse but will be at a slower rate
Electrocardiogram (EKG)
 Graphic record of heart’s electrical activity
P wave
 Depolarization
of the atria,
passage of
electrical
impulse from
SA node thru
the atria
QRS complex
 Represents
depolarization
of ventricles
 Repolarization
of atria also
occuring
T wave
 Repolarization
of ventricles
http://www.youtube.com/watch?
v=qHjbEYUfzH8
Cardiac cycle
 Complete
pumping
cycle
 Systole
(contraction)
& diastole
(relaxation)
of atria &
ventricles
Atrial systole
 Contraction of atria
 Blood into ventricles
 AV valves are open
 Semilunar valves
closed
 P wave of EKG
Isovolumetric Ventricular
Contraction
 Between start of
ventricular systole &
opening of semilunar
valves
 Ventricular volume
constant
 Ventricular systole
coincides with R
wave of ECG & 1st
heart sound
Ejection
 Semilunar valves open
 Initial rapid ejection:
marked increase in
aortic & ventricular
pressure
 Longer reduced
ejection: T wave
appears
 Residual volume of
blood remains in
ventricles after ejection
Isovolumetric Ventricular
Relaxation
 Ventricular diastole
 Period between
closure of
semilunar valves &
opening of AV
valves
 Second heart
sound is heard
Passive ventricular filling
 Av valves forced
open by
increasing intra
atrial pressure
Heart sounds
 “lubb-dupp”
 First sound caused by contraction
of ventricles & vibrations of the
closing of AV valves
 Second sound caused by
vibrations of the closing of
semilunar valves
Factors that affect heart rate
 Anxiety, fear,
anger
 Exercise
 Increased body
temperature
 Grief
 Decreased body
temperature
Venous Return to Heart
 Blood pumping
action of
respirations
 Skeletal muscle
contraction
Blood pressure
 Sphygmomanometer
 Systolic pressure:
force with which the
blood is pushing
against the artery
when ventricles are
contracting
 Diastolic pressure:
force of blood when
ventricles are
relaxed
Pulse
 Alternate expansion & recoil of an
artery
 Two factors are responsible
 Intermittent injections of blood from
heart
 Elasticity of arterial walls
Pulse sites
 Radial artery- wrist
 Temporal arterytemples
 Carotid artery- neck
 Brachial arteryelbow
 Popliteal arterybehind knee
 Dorsalis pedis- top
of foot