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Transcript 
Circulatory
System
How does the heart
work?
Heart beat
 The
heart is myogenic
Generates
its own electricity
Motor nerve
Skeletal muscle
Heart beat
 Sinus
node
Plexus
Sinus Node
(SA Node)
of nerves
Initiates
contraction of
cardiac muscle

Atria
Heart’s
“natural
pacemaker”
Heart beat
 AV
node
Receives
Sinus Node
(SA Node)
Atrioventricular
Node (AV
Node)
impulse from SA
Node
Delivers impulse
to the HisPurkinje System
Heart beat
 Bundle
of His
Begins
Sinus Node
(SA Node)
Atrioventricular
Node (AV
Node)
Bundle
of His
conduction to the
ventricles
Heart beat
 Purkinje
System
Bundle
Sinus Node
(SA Node)
Atrioventricular
Node (AV
Node)
Bundle
of His
Purkinje Fibers
branches
Purkinje fibers
Moves the
impulse through
the ventricles for
contractions
Bundle Branches
Heart beat
SA
node
both atria
contract
AV node
0.1 second delay
Both ventricles
contract
Heart beat


Pacemaker is controlled by
the medulla oblongata
Sympathetic nerves can speed heart rate up
 Noradrenaline


Increases rate of cardiac muscle contraction
Parasympathetic nerves can slow heart rate
down
 Acetylcholine


(neurotransmitter)
(neurotransmitter)
Decreases rate of cardiac muscle contraction
Adrenaline (hormone) may also increase heart
beat
Heart sounds (lub-dub)
0.1 sec delay results in
2 sounds
 Results from closing of
valves

 “lub”

Recoil of blood against
closed AV valves
 “dub”


Recoil of blood against semilunar valves
Heart murmur
 defect
in valves causes hissing sound when stream of
blood squirts backward through valve
Cardiac cycle

1 complete cycle of pumping
 Heart
contracts & pumps
 Heart relaxes & fills
 Contraction phase
 Systole
 Ventricles pump blood out
 Relaxation phase
 Diastole
 Atria/ventricles fill with blood
systolic
________
diastolic
pump
(peak pressure)
_________________
fill (minimum pressure)
110
____
70
Measuring of blood pressure

High Blood Pressure (hypertension)
 if
top number (systolic pumping) > 150
 if
bottom number (diastolic filling) > 90
Electrocardiogram (ECG or EKG)

Measures electrical impulse through heart
Electrocardiogram – P wave

Atrial depolarization
 Caused
by impulse from SA Node
Electrocardiogram – PQ segment

Delay at AV Node
Electrocardiogram – PQ segment

Conduction of impulse through Bundle
Branches
Electrocardiogram – PQ segment

Conduction of impulse through Purkinje
Fibers
Electrocardiogram – QRS wave

Ventricular depolarization
 Ensures
synchronized contraction of ventricles
Contraction begins at apex
Electrocardiogram – ST segment

Interval between ventricle depolarization
and repolarization
Electrocardiogram – T wave

Ventricle repolarization
Normal EKG activity
Putting it all together …
Any questions?
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