1. 46 micrometres, which means 22 can fit into one millimetre.
Blood 4 Damage: Cells 1
Student Sheet 1
Heart muscle cells
Contains fibres that can make the cell contract (get shorter) or let it spring back to its original length.
Cells contain lots of mitochondria for obtaining energy.
Dies quickly if its blood supply is cut off.
Needs plenty of glucose and oxygen to keep working.
46 micrometres, which means 22 can fit into one millimetre.
Can keep contracting about 70 times a minute for a whole lifetime.
Has branches and is joined very firmly to the next heart muscle cell.
If too many die the heart cannot work as hard.
Heart credit: Patrick J. Lynch 1

2. Melanocytes Blood 4 Damage: Cells 2 Student Sheet 2
skin surface
Make a brown pigment called melanin, which gives skin, eyes and hair their colour.
Found at the bottom of layers of skin cells.
melanocyte
melananin
Killed by deep burns so that the skin grows back with no melanin in it.
Their long thin arms squeeze between skin cells and pass melanin to them.
The difference between skin colours depends on the melanin that melanocytes make.
7 out of skin cells are melanocytes.
7 micrometres
Skin credit: US National Cancer Institute
143 can fit into 1 millimetre 2

3. Red blood cells Blood 4 Damage: Cells 3 Student Sheet 3
Full of a red chemical called haemoglobin that contains iron.
People who do not get enough iron in their diet have small, pale red blood cells and feel tired all the time.
Haemoglobin picks up oxygen in the lungs and releases it in other parts of the body.
People who lose a lot of blood have normal red blood cells but too few of them.
The thin shape means that it can bend to fit through tiny blood vessels and oxygen can get in and out the cell easily.
Stem cells in the centre of bones make about 2 million new ones per minute.
2 micrometres
thick
New red blood cells have a nucleus but as they mature in bone marrow they break down their nucleus to make space for more haemoglobin.
143 can fit into 1 millimetre
7 micrometres
diameter
Healthy adults have about 20,000,000,000,000 red blood cells.
Photo credit: visualsonline.cancer.gov 3

4. Cilliated cells Blood 4 Damage: Cells 4 Student Sheet 4
Ciliated cells cover the airways down to the lungs.
Each cell has about 200 tiny hairs called cilia that wave backwards and forwards.
There are lots of mitochondria in the cytoplasm between the nucleus and the cilia.
Special cells next to them make a sticky fluid called mucus that coats the top of the cilia.
This helps to stop the airways and lungs from getting an infection.
Dirt and microbes stick to the mucus and get brushed to the back of the throat to be swallowed.
24 micrometres
6 micrometres
33 can fit into 1 millimetre
The poisons in tobacco smoke paralyse the cilia. 4

5. White blood cells Blood 4 Damage: Cells 5 Student Sheet 5
More of these are produced when you have an infection.
They have unusual shaped nuclei.
When they catch a microbe they change shape, wrap themselves around it and take it into their cytoplasm.
They move through blood vessels until they find microbes.
Inside their cytoplasm are little bags of chemicals that can destroy most microbes.
13 micrometres
77 can fit into 1 millimetre
They can squeeze out of blood vessels to attack infections in other tissues.
SEM of white cell destroying microbes 5

6. Nerve cells Blood 4 Damage: Cells 6 Student Sheet 6
They pass messages from one end of the cell to the other (like a wire carries electricity).
The message travels down the long thin part of the cell called the axon.
The ones that take messages from your spine to your muscles are very long.
If the axon is damaged then the message cannot get through.
They come in lots of different shapes and sizes.
Up to 1 metre
( 1,000,000 micrometres)
message goes this way
Some conduct messages from one part of the brain to another and are very small.
Nerve cells cannot divide and are very bad at repairing themselves.
Message goes this way
Some conduct messages from sense organs like your skin to your spine.
If the nerve cells in your spine are damaged, then messages cannot be passed from your brain to your muscles or from your skin to your brain.
Nerve cells 6

7. Operations are more dangerous for overweight people.
Blood 4 Damage: Cells 7
Student Sheet 7
Fat cells
You have about 30 billion fat cells – more if you are female.
Most of the cell is filled with a large droplet of fat in the middle so the nucleus and cytoplasm are squashed to the edge.
Their main job is to store fat to give us energy between meals.
The layer under your skin helps you keep warm.
When we eat more than we need to, the extra is converted to fat and stored in these cells.
The layers around your organs protect them from damage.
Fat cells can blow up to three times their normal size to store more fat.
nucleus
cytoplasm
fat droplet
50−150 micrometres
6−20 can fit into a millimetre
SEM of fat cells
Once they reach their maximum size they can divide to make more.
Storing too much fat increases your chance of developing heart disease and diabetes.
Operations are more dangerous for overweight people. 7

8. Bone cells Blood 4 Damage: Cells 8 Student Sheet 8 X
Bone cell stained with fluorescent dye
The cytoplasm of bone cells makes a substance called collagen.
The collagen is pushed outside their cell membrane through little tentacles.
The collagen jelly collects minerals like calcium and becomes hard bone.
collagen jelly
The bone cells become stuck in the hard bone they have made but they are still alive.
If a bone gets broken, new bone cells go to the break to make more hard bony material.
bone
bone cell
Bones contain lots of living cells and have small blood vessels running through them.
If you don’t eat enough calcium your bones can’t harden properly. X 8