KS4 Blood Vessels

Topics: Blood vessel, Blood, Artery Pages: 29 (1020 words) Published: March 10, 2015
KS4 Biology

Blood Vessels
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Contents

Blood Vessels
What blood vessels do
Arteries
Veins
Capillaries
Summary quiz
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© Boardworks Ltd 2004

What blood vessels do
We can get an idea of what they could look like from
considering the job they have to do.
Let us look at a small section of the circulatory system.
There seems to be 3 types of blood vessel present.
one joins the
other two
together

one takes
blood away
from the
heart

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Lungs

one takes
blood to the
heart
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Three broad types of vessels
1.
Blood vessels that take blood away from
the heart are known as ARTERIES.
ARTERIES
Remember, arteries (away)

2.
Blood vessels that take blood back to
the heart are known as VEINS.
VEINS
Remember, veins
in (into
in the heart)

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and in between…
3.

Finally, if arteries take blood away from the
heart and veins take blood back to the heart,
when does an artery turn into a vein?
Well, our third type of blood vessel links the two.
We find it present where an artery finishes and a
vein is about to begin.
This third type of blood vessel
is known as a CAPILLARY.

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© Boardworks Ltd 2004

Contents

Blood Vessels
What blood vessels do
Arteries
Veins
Capillaries
Summary quiz
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© Boardworks Ltd 2004

Artery cross-section

small
lumen

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thick muscle
and elastic
fibres

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Arteriole pressure
The small size of the lumen means that
blood will be under high pressure.
The thick fibrous wall strengthens
the artery.

Imagine using a water hose and
putting your thumb half over the
open end.
The water is released under higher
pressure and it flows faster.

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Properties of arteriole walls

thick arteriole wall
lumen

The elastic allows the artery to stretch under pressure
whilst the muscle can contract to push the blood along.

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The human pulse
This stretching of the artery is what allows us to feel a pulse. As the heart beats, it releases regular surges of blood. As
these pass along the arteries, the vessel must stretch to
allow the increased blood flow to pass.
This stretching pushes on the skin, which we sense as a
pulse.

blood
flow

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blood
flow

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Blood flow in arteries
The blood flowing through an artery will be under high
pressure and moving extremely fast.
There is no chance that the blood will turn around and
start travelling in the opposite direction.

Therefore, there are no valves present in arteries.

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© Boardworks Ltd 2004

Contents

Blood Vessels
What blood vessels do
Arteries
Veins
Capillaries
Summary quiz
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© Boardworks Ltd 2004

Veins: cross-section

large lumen

thin muscle and
elastic fibres
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Walls of veins
The lumen of a vein is much
thicker than the wall that
surrounds it.
There is less of a need to
maintain a high pressure.

The walls still contain elastic and muscle but there is
far less present compared to the artery.
You will appreciate that the blood is flowing far less quickly through veins compared to arteries.
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Getting another boost
The veins are carrying blood back towards the heart.
Materials have been exchanged and now it is running
out of energy.
It needs to return to the heart to receive another pump.

Unfortunately, this could lead to a real

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problem...

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Preventing backflow
Q. What would happen if blood loses so
much energy that it stops and turns around?
leg

gravity
vein

Normal
direction of
blood flow

This situation could arise where blood is flowing against
gravity.
However, there is a solution to this problem and it comes in two parts.
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