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From the moment it begins beating until the moment
it stops, the human heart works tirelessly.
• Red blood cells transport
oxygen from lungs to all
RESPIRING tissues
• Contain heamoglobin
containing iron which picks
up oxygen at the lungs and
lets go of it at tissues
• No nucleus so more space
for heamoglobin
• Small and flexible so can
squeeze through narrow
capillaries.
• THE BLOOD FLOWS
AWAY FROM THE
HEART IN VESSELS
CALLED ARTERIES.
• Blood is at high pressure
• Blood is rich in oxygen and
low in carbon dioxide
• Elastic walls expand and
relax as blood is forced out
of the heart. (this causes the
‘pulse’)
• Thick walls to stand the high
pressure of blood.
• The rings of muscle get narrow
or widen the artery to controll
the blood flow.
• BLOOD FLOWS
BACK TOWARDS THE
HEART IN VESSELS
CALLED VEINS.
• Blood is at low pressure
• Blood is low in oxygen
and high in carbon dioxide
• Valves prevent the
backflow of blood.
• Even though
blood is at low
pressure, nearby
muscles squeeze
veins and push
blood back
towards the heart.
• The large
diameter and
thin walls
reduce the
resistance of
the flow of
blood
• The walls of capillaries are one
cell thick
• They are highly branched so
they cover an enormous surface
area (more space for diffusion
between capillaies)
• They are constantly supplied
with fresh blood, keeping up the
concentration gradients
JOINING ARTERIES AND VEINS ARE
THE CAPILLARIES
The
arrangement of
the circulatory
system is called
a double
circulation
because the
blood travels
twice through
the heart for
every complete
circuit
• If the
pressure is too
high in the
pulmonary
artery, tissue
fluid or plasma
can leak into
the lungs.
1. The Blood flows
to the lungs under
high pressure.
2. Then having
picked up oxygen
at the lungs the
blood recieves
another boost
form the heart.
3. This drives it out
to the tissues to
deliver the
oxygen.
Pressure is generated by the squeezing of the walls of the heart against the
fluid blood.
PULMONARY ARTERY
– carries deoxygenated
blood to the lungs.
SEMILUNAR VALVES –prevent
backflow of blood when pressure
falls during relaxation.
AORTA – the main
artery of the body.
Carries oxigenated
blood out to the
body.
PULMONARY VEIN – returns
deoxigenated blood from lungs.
LEFT ATRIUM - recieves oxygenated
blood returning from the lungs. It has
thin walls as they only pump blood to
ventricles.
VENA CAVA – the main vein of
the body. Returns deoxygenated
blood from the body.
BICUSPID VALVE – when this is closed
and ventricle contracts, blood leaves
through aorta.
RIGHT ATRIUM –
recieves deoxygenated
blood.
LEFT VENTRICLE
WALL OF LEFT
VENTRICLE – thick and
muscular as it forces
blood round whole body
TRICUSPID VALVE – prevents
back flow of blood during
contraction.
TENDONS – tightened
to make sure valve
doesn’t turn inside out
when ventricle contracts.
RIGHT
VENTRICLE
WALL OF RIGHT VENTRICLE –
less muscular than left ventricle as it
only pushes blood to the lungs .
• The muscular walls of the heart
are different from other muscles
because they never become tired
• This is because each contraction
is immediately followed by a
relaxation, allowing the heart to
recover.
• These contractions and
relaxations are kept by electrical
signals sent from a part in the
heart called the pacemaker.
If any of the cornonary arteries
become blocked the supply of
blood to the heart muscle may be
interrupted
The muscles wouldnt get the
oxygen and glucose they need, so
poisonous wastes like lactic acid
would build up
Then part of the heart muscles
stops contracting which causes a
HEART ATTACK!
Risk of coronary heart disease is
increased by:
• Poor diet (eg.cholesterol)
• Poor lifestyle (eg. Smoking etc.)
• Genetic factors (family history)
If the coronary arteries are
blocked, a CORONARY
ARTERY BYPASS operation
may be carried out. (see above)
• A pacemaker is a specialised
piece of tissue in the wall of the
right atrium
It makes sure that:
1. The atria contract just before
ventricles for flow
2. The heartbeat is fast enough for
the demands for oxygen and
nutrients etc.
If the pacemaker doesnt work
as well as it should, an artificial
one can be fitted in the chest.
It is made up of a box
containing batteries and an
electronic timing device.
During exercise the muscles work hard, they
need more oxygen and glucose to release
energy by respiration. This means they need an
increased circulation of blood to deliver these
materials.
For this to
happen:
• The heart pumps
more blood each
minute
• Sphincters
control
distribution of
blood