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What are bones made of?

When we think about what a bone is made of, we usually imagine it to be a dry and hard substance that doesn’t appear to be ‘living’ in any way.

In fact, the bones in our bodies are filled with living material: there are blood vessels which run near the surface of the bone, and two layers of bone types, compact bone and spongy bone. Often there is a jelly-like area in the centre of the bone, which is called the bone marrow. Bone marrow produces the body's blood cells. Red blood cells carry oxygen around the body and white blood cells fight infection within the body.

A cross section of an arm showing the bone   If you looked at a cross section of your arm, you would be able to see that the bone is actually a hollow structure; in the middle is a cylinder.

Strong and light : bamboo scafolding   So, bones are actually hollow tubes, a bit like bamboo which is a type of plant. A hollow structure means that the weight of the bone is a lot less than it would be if it were solid.

But try applying force on the top and then the sides of a drink can. What happens? What price do we pay for having light bones?

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Have a look at the Extreme Limits and see what happens when different forces are applied to bones. What do these clips have in common (apart from being gory!)?
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What do bones do?

If you have already seen Casing the Joint you’ll already know the answer to this question!

Different types of animals have different skeletons, depending upon what they need them to do.

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Try to Build a Skeleton and try to work out what the differences and similarities are between the types of skeletons.

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ribcage   Bones in the human body are not only concerned with forming a strong structure which holds our bodies up and helps us move; they are also there to protect our internal organs. For example, if you didn’t have a ribcage, your heart would be very vulnerable. Bones also store essential body minerals, and bone marrow produces new cells for our bloodstream.

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What happens in unhealthy bones?

Our bodies are constantly replacing bone tissue and our ability to do this is dependent upon the minerals we have in our blood.

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What do you think would happen to your bones if you didn’t have the right kind of minerals in your blood?
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Osteoporosis is a condition that can occur if the body cannot make enough new bone building material. This is because the person does not have the right mineral levels in their bloodstream. The result is that bones become larger and more fragile.

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It is unusual for young people to suffer from osteoporosis, but your diet and lifestyle will affect your health in later life so you need to ensure that your diet is rich in calcium.

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For more information, visit the National Osteoporosis Society

stem cell   When bone marrow is unable to produce healthy red blood cells patients may suffer from life threatening conditions such as Leukaemia or Hodgkin’s disease. Treatments such as chemotherapy kill the damaged stem cells in bone marrow but also destroy important healthy tissue. Can our bodies heal themselves? Can we control artificial limbs with our brains? Find out in the Big Questions.

In a transplant, a patient’s damaged bone marrow is destroyed and healthy marrow is introduced into the blood stream. The new tissue migrates to the cavities within large bones and begins to produce healthy blood cells once more.

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Arthritis is a condition that makes the joints swell. This swelling is the result of bones rubbing against each other without the protection of cartilage. If you suffered from arthritis of the knee, you would be unable to straighten or bend your knee fully and moving it would be very painful.

Sadly there is no cure for this condition, but joints may be replaced with steel or plastic to make artificial bone and cartilage.

For more information about arthritis, visit:


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