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Blood and Oxygen
Your circulatory
and
respiratory system
Why do we need a circulatory
system?
The human body is large and so it needs a
system to transport what it needs around.
 This system is The Circulatory System and
it does 3 things;

– Supplies oxygen
– Supplies nutrients
– Removes wastes (eg Carbon dioxide)
What is it made of?
 The
circulatory system is made up of;
– Vessels. Eg. Arteries, veins and
capillaries.
– A pump. In the case of mammals a
heart.
The heart (the pump)
 In
humans the heart is located behind
the lungs in the centre of the chest
slightly leaning to the left.
 The
heart has two atria (chambers on
the top of the heart) and two
ventricles (very muscular chambers
on the bottom)
The Vessels
Blood vessels are not all the same size.
They get smaller in diameter as you move
further from the heart.
 There are three main types of blood
vessels;

– Arteries
– Veins
– Capilliaries
Arteries
Arteries carry blood away from the heart,
delivering oxygen and nutrients to cells
and tissues.
 Arteries have very thick walls which
contain a lot of elastic tissue and muscle
to help them withstand the pressure
produced by the heart.

Veins
Veins carry blood back from the cells and
tissues to the heart so it can be pumped
into the lungs for re-oxygenation.
 Veins have thinner walls than arteries,
which contain less elastic tissue and
muscle.
 Veins contain one way valves which
prevent blood flowing the wrong way.


These valves are important in returning
blood from the legs against gravity.
Capillaries
Capillaries are very narrow they are only
wide enough for one red blood cell to pass
through at a time.
 The walls of capillaries are only one cell
thick.
 This means that in capillaries, substances
are able to be transferred across the cell
membrane into and out of the blood
stream.
