Download The Cardiovascular System

The
Cardiovascular
System
CONDUCTION SYSTEM
Activity 1
Draw and label in as much detail as
possible the chambers of the heart
and surrounding structures.
Activity 1
Now complete the following diagram
on the worksheet provided
Activity 2
We will now add more detail to the
heart this information is known as the
‘Conduction System’
How the Heart Works
• The heart works by producing impulses
which spread and innervate the specialised
muscle fibres.
• Unlike skeletal muscle, the heart produces
its own impulses (it is myogenic), and it is
the conduction system of the heart which
spreads the impulses and enables the heart
to contract.
http://www.youtube.com/watch?v=te_SY3MeWys&feature=related
How the Heart Works
• The electrical impulse begins at
the pacemaker: a mass of
cardiac cells known as the sinoatrial node (S.A. node).
• It is the rate at which the S.A.
node emits impulses, that
determines heart rate.
• As the impulse is emitted, it
spreads to adjacent
interconnecting fibres of the
atrium, which causes the atria
to contract.
• It then passes to another
specialised mass of cells called
the atrioventricular node (A.V.
node).
How the Heart Works
• The A.V. node acts as a
distributor and passes the
action potential to the Bundle
of His, which, together with the
branching Purkinje fibres,
spread the excitation
throughout the ventricles.
• There is a delay of about 0.1
second from the time when the
A.V. node receives stimulation,
to when it distributes action
potential through the
ventricles.
How the Heart Works
• This is crucial to allow
completion of atrial
contraction, before
ventricular systole begins.
• The relationship between
the electrical activity of the
heart and the cardiac cycle
can be shown in an
electrocardiogram (ECG)
Summary
1) Heart generates own electrical impulses,
2) At the sino-atrial node (pacemaker),
3) Impulse spreads through cardiac tissue in
the atria,
4) This causes contraction of the atria,
5) The impulse carries on to Atrio-ventricular
node,
6) The action potential moves into Bundle of
His and spreads throughout the Purkinje
fibres causing the ventricle to contract.
Introduction to the
Cardiac Cycle
• It is the process of cardiac contraction and
blood transportation through the heart.
• We are going to explain the sequence of
events that takes place during one complete
heartbeat.
• Including filling and emptying of the blood
into the arterial system.
1) Atrial
Diastole
2) Ventricular
Diastole
3) Atrial
Systole
4) Ventricular
Systole
What does
all this really
mean?
Diastole
means that
heart is filling
Systole means
that the
heart is
emptying
Four Stage to Each Beat
Atrial Diastole
• Takes the 0.7 seconds.
• The upper chamber of the heart are filled with
blood returning from;
• The body via the venae cavae to the right atrium.
• The lungs via the pulmonary vein to the left atrium.
• At this time the AV valves are shut but as the
atria fill with blood, atrial pressure overcomes
ventricular pressure.
• Since blood always moves from areas of high
pressure to areas of low pressure, the
atrioventricular values are forced open and
ventricular diastole now takes place.
Ventricular Diastole
• 0.5 seconds
• During this stage the ventricles fill with blood
and the semi-lunar valves remain closed.
• The atria now contract, causing atrial systole.
Atrial Systole
• Takes 0.1 seconds.
• The atrial contraction ensures that all the blood is
ejected into the ventricles.
• As the ventricles continue going through diastole, the
pressure increases, which causes the atrioventricular
valves to close.
• Ultimately the ventricular pressure overcomes that in
the aorta and the pulmonary artery.
• The semi-lunar values open and the ventricles
contract, forcing all the blood from the right ventricle
into the pulmonary artery and the blood in the left
ventricle into the aorta.
• This is ventricular systole.
Ventricular Systole
• 0.3 seconds
• Once completed, the semi-lunar values snap
shut.
• The cycle is now complete and ready to be
repeated.
HOW THE HEART WORKS
Heart rate is controlled by 3 factors:
•
The AUTONOMIC NERVOUS SYSTEM which consists
of the PARASYMPATHETIC (returns heart to resting
level)& SYMPATHETIC SYSTEM (stimulates heart to
beat faster)
•
2 systems co-ordinated by the CARDIAC CONTROL
CENTRE (c.c.c.) in the MEDULLA OBLONGATA
•
The CCC is stimulated by CHEMORECEPTORS
(chemical changes) & BARORECEPTORS (pressure in
blood vessels)