Transcript blood vessels

Key Stage 4
Blood Vessels
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Now, let’s consider the blood vessels...
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
Lungs
One takes
blood to the
heart
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So we have 3 types of blood vessels doing 3 different
jobs.
1.
Blood vessels that take blood away
from the heart are known as
ARTERIES.
Remember, arteries (away)
2.
Blood vessels that take blood back to
the heart are known as VEINS.
Remember, veins (into the heart)
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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. In
other words, 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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Let us consider each vessel in turn to see how its
shape is related to the job it has to do.
In each case we will look at a cross-section of the vessel
ARTERY
small
lumen
thick muscle
and elastic
fibres
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The small lumen means that
blood will be under high
pressure.
(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.)
The thick fibrous wall strengthens the artery. The elastic
allows the artery to stretch under pressure whilst the
muscle can contract to push the blood along.
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This stretching of the artery is what allows us to
feel a pulse.
As the heart beats, it releases regular surges (increased
volumes) of blood. As these pass along the arteries, the
vessel must stretch to allow it to pass. This stretching
pushes on the skin, which we sense as a pulse.
skin surface
Blood flow
Blood flow
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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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VEINS
large lumen
thin muscle and
elastic fibres
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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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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
human
leg
vein
Problem..
What happens
if blood loses
so much
energy that it
stops and
turns around?
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This situation could arise where blood is flowing
against gravity. However, there is a solution to this
problem. It comes in two parts.
1.
Firstly, veins have valves which act to stop the
blood from going in the wrong direction.
(These valves are similar to those found in the heart)
valves
open
valves
close
blood
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2.
The second part of the solution has to get the
blood flowing again whilst overcoming the problem
of a lack of muscle in the lining of the vessel.
The solution comes in the form of general body muscles
that surround the veins. When these muscles contract
to move the body, they also squeeze the veins and push
the blood along the vessel.
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CAPILLARIES
These vessels link arteries with veins.
They are found all over the body and are essential for
the exchange of materials between the blood and other
body cells.
artery
vein
capillaries
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Capillaries are so small
that they can only be seen
using a microscope.
A collection of capillaries is
known as a capillary bed.
The wall of a capillary is
only one cell thick!
very narrow lumen
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Substances can diffuse across the lining of the
capillary. This allows useful substances which are
dissolved within the blood to move into surrounding
cells whilst cellular waste moves in the opposite
direction.
3
1
2
The exchange of materials between the blood and the body
can only occur through capillaries.
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One such exchange that occurs in the capillaries is
that of oxygen and carbon dioxide.
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Multiple choice questions
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What is the name of blood vessels that take
blood away from the heart?
A veins
B tubes
C capillaries
D arteries
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Which of the following vessels has a wall that is
only one cell thick?
A capillaries
B arteries and capillaries
C veins
D arteries
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Blood returning to the heart from the body
has a higher percentage of carbon dioxide
within it. Which of the following statements
explains this phenomenon?
A The blood has produced more carbon dioxide as it
flows around the body.
B The blood has picked up the carbon dioxide from
cells that have been performing respiration.
C The body has turned the blood cells into carbon
dioxide.
D The oxygen in the blood has turned into carbon
dioxide.
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When blood returns from the lungs to the heart,
it contains more oxygen than it did when it left.
Which of the following statements explains why
this is so?
A The blood returning from the lungs has a low
concentration of carbon dioxide.
B The haemoglobin in the red blood cells binds to the
oxygen.
C The carbon dioxide is dissolved in the plasma.
D The blood contains a higher concentration of oxygen
than the air when it arrives back at the lungs.
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As red blood cells flow through the capillaries
between muscle cells they…
A pass out of the capillaries.
B pick up oxygen.
C will release carbon dioxide.
D release oxygen by splitting up their oxy-haemoglobin
molecules.
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The blood flows through the arteries…
A slowly at high pressure.
B quickly at low pressure.
C slowly at low pressure.
D quickly at high pressure.
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Blood flows through the veins…
A slowly at high pressure.
B quickly at low pressure.
C slowly at low pressure.
D quickly at high pressure.
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In the organs, blood flows through…
A large, thick-walled blood vessels.
B narrow, thick-walled blood vessels.
C large, thin-walled blood vessels.
D narrow, thin-walled blood vessels.
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What is the job of the valves that are found
within both the heart and veins?
A To stop blood going in the wrong direction.
B To speed up the flow of blood.
C To check the contents of blood.
D To stop the blood flowing.
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Which of the following statements describes the
flow of blood through a vein?
A The veins contract and relax in a wave like fashion,
forcing the blood in the right direction.
B The veins have valves, which prevent blood from
flowing backwards. Skeletal muscles squeeze
against the veins and push the blood along.
C The veins have valves which push the blood in the
right direction and elastic walls which force the blood
along.
D As blood is pumped out of the heart the blood is
sucked along the veins.
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