The Circulatory System - Session 2
Blood
Cells
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The Circulatory System – Session 1 Recap
Recap what we learnt about the heart and blood
vessels.
What does your heart do?
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Why does your heart need to work all the time?
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What is your heart rate? Is it always the same?
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Why does your heart beat faster when you exercise?
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What different types of blood vessels does your
blood travel through?
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What is blood made of?
What do you think your blood is made of?
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55 % plasma – the liquid part
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45 % blood cells
– Almost all red blood cells (99%)
– A few white blood cells
– Platelets
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Separating blood cells from plasma
plasma
white blood cells
red blood cells
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Make blood
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One cup of jelly
10 -15 grains of rice
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a clear, strong plastic bag
water
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Put the jelly into the plastic bag
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Squeeze it a few times to break up the jelly
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Add 10 to 15 grains of rice
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Add one cup of water
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Mix
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Red Blood Cells
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What shape are
they?
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What do they do?
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Why are they red?
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How big are they?
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How many in a drop
of blood?
Image from https://smorgasbordinvitation.files.wordpress.com/2015/06/red-blood-cells.jpg
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How many red blood cells are in your body?
Red blood cells are tiny, about 7 micrometres
across. You need a microscope to see them.
There are about 5 million red blood cells in one
microlitre of blood. That’s a very tiny drop of blood
– a teaspoon can hold 5,000 microlitres.
Your body contains about 3 litres of blood. How
many red blood cells are in your body?
(1 microlitre is 1 millionth of a litre)
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How many red blood cells - calculation
5 million red blood cells in 1 microlitre of blood:
5,000,000 x 1,000,000 =
5,000,000,000,000
red blood cells in 1 litre of blood
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Around 3 litres of blood in your body:
5,000,000,000,000 x 3 =
15,000,000,000,000 (15 trillion)
red blood cells in your body
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Transporting Oxygen and Carbon Dioxide
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Oxygen sticks to haemoglobin in blood while it’s
being pumped through your lungs
Oxygen leaves haemoglobin when blood reaches
cells that need it
Carbon dioxide sticks to haemoglobin when it has
been produced by cells
Back in the lungs, the carbon dioxide is released
from haemoglobin to be breathed out
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Red blood cells squeeze through capillaries
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Make a ball of dough about 4 cm across
Squash the middle to flatten it to
the shape of a red blood cell.
Make your dough cell a bit wider
than the hole in a toilet roll tube
If you have some plastic film, wrap your cell in it
Hold a toilet roll tube in one hand around the outside
to help it keep its shape. Try to push your cell through
the tube.
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Squashy red blood cells
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Red blood cells are a bit bigger than capillaries.
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They get squashed out of shape when they travel
through capillaries.
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They have to be strong and flexible so they are not
damaged when they are squashed.
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Being squashed up against the walls of capillaries
makes it easier and quicker for oxygen to travel out
from red blood cells to cells that need it.
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White blood cells
There are about 10,000 white blood cells in 1
microlitre of blood.
There are several different types of white blood cells.
They help our bodies to fight off infections by killing
germs like bacteria and viruses.
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Phagocytosis
Some white blood cells can chase and eat
bacteria. This is called phagocytosis.
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Clotting
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How does bleeding stop?
If you get a cut or graze you might bleed for a bit.
This can help wash away harmful bacteria.. But after
a little while, the bleeding stops.
It is important that our bodies don’t lose too much
blood. When a blood vessel is damaged, blood
thickens and makes a plug to stop any more
escaping.
This is called clotting.
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How blood clots
①platelet
②red blood cell
③wall of blood vessel
④clot
⑤ fibrin
⑥ active platelet
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Questions for you
Red blood cells are unusual cells. How are red blood cells
different from other cells in your body?Look at a diagram of a
typical animal cell. Think about what you have learnt about red blood
cells. What do they look like, what is inside them, what can they do?
How is this different from other animal cells?
People who live at high altitude (in high mountain ranges)
usually have more red blood cells per microlitre of blood, as
well as a larger volume of blood in their bodies. Why do you
think this is?
What percentage of the cells in your body are red blood cells?
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