Physiology of the heart
The Heart as a Pump
The ventricles serve as the force behind the
pump.
Specialized structures called intercalated
disks allow cells to beat in synchrony. This
coordinated heartbeat is call interstitial
syncytium and makes the heart a more
effective pump.
What is the definition of a
heartbeat?
Heartbeat
Definition: a single sequence of atrial
contraction followed by ventricular
contraction.
Contraction:the process in which a
muscle becomes or is made shorter
and tighter.
Heartbeat vs Pulse
Heart rate is the number of times per
minute that the heart contracts - the
number of heart beats per minute.
Pulse is the mechanical movement of
blood flow through the capillaries
caused by the contractions of the heart
per minute.
The number of heartbeats per minute
should be the same the pulse count
True
False
Heartbeat
▪ Normal rate: 60-100
What affects the rate ?
●
●
●
●
Age
Fitness level
Presence of certain medical conditions
Some drugs including caffeine and
nicotine.
7
Heart sounds
▪ Called S1 LUB and S2 DUB
▪ S1 is the closing of AV (Mitral
and Tricuspid) valves at the
start of ventricular systole
▪ S2 is the closing of the
semilunar (Aortic and
Pulmonic) valves at the end
of ventricular systole
8
Some terms to know
▪ Slow heartbeat: bradycardia
▪ Fast heartbeat: tachycardia
▪ Systole: the highest blood pressure that
occurs as the ventricles contract
▪ Diastole: the blood pressure when
ventricles are relaxed and filling.
A young man has a pulse of
120. He is suffering from
Action Potential
Cells have a negative membrane potential.
A signal from a nerve allow ions to enter
the cell changing the potential and forcing
the cell to contract.
Repolarization=Relaxation
Depolarization = Contraction
“EKG”
(or ECG, electrocardiogram)
▪ Electrical
depolarization is
recorded on the body
surface by up to 12
leads
▪ Pattern analyzed in
each lead
P wave=atrial depolarization
QRS=ventricular depolarization
T wave=ventricular
12
repolarization
Label diagram in
your notebook
Electrical conduction system:
The system is
composed of
specialized cardiac
muscle cells that carry
impulses throughout the
heart musculature.
These cells signal the
chambers to contract in
the proper sequence.
(Explanation in next slides)
14
Parts of the Conduction system
SA node (sinoatrial)
-Located in the upper wall of Right Atrium
-Sets heart rate: 70-80
-Is the “natural” pacemaker
AV node (atrioventricular)
-Located in the lower wall of the right atrium
-It receives the impulse from SA node as it
moves toward the right ventricle. 15
Conduction continued
AV bundle (bundle of His)
▪ Found in the interventricular septum
▪ The AV bundle divides into right and left
bundle branches which deliver the impulse
to the bottom of the heart.
The Purkinje fibers
complete the signal by
spreading the impulse
through the outer walls
of the ventricles.
16
Right and
left
Bundle
branches
SA
Node
AV
node
Purkinjie
Fibers
Artificial
Pacemaker
19
Coronary Circulation
The heart has its very own blood vessels!
The blood inside the heart does not supply
the heart muscle.
On the outside of the heart you see
coronary vessels that supply the heart
muscle.
Myocardial infarction
When the blood supply
to the heart muscle is
blocked, The tissue
dies.
This is what causes a
heart attack
another flow chart
23
Use to
study
24
Starting from the
outside…
Pericardium
(see next slide)
Without most of pericardial
25
Coverings of the heart: pericardium
▪ 2 layers of pericardium
▪ Parietal layer of serous pericardium
▪ Visceral layer of serous pericardium =
epicardium: on heart and is part of its wall
(Between the layers is pericardial cavity)
26