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the bones in our bodies are alive

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growing and changing all the time

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our bones are composed of different

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layers the outer surface of bone is

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called cortical bone this is the smooth

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hard part of the bone that we can see

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when we look at a skeleton inside the

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cortical bone is the trabecular bone

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this type of bone looks like a sponge

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and helps to protect the bone marrow

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the constant process of bones growing

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and changing is known as bone remodeling

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this process is carried out by specific

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cells in our bones cells called

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osteoclasts have the role of breaking

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down our bone and removing any parts

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that need replacing

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at the same time cells called

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osteoblasts have the job of making new

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bone and helping to repair any parts of

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the bone that have been damaged

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on earth in healthy individuals this

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process is normally balanced so that the

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same amount of bone is made and broken

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in space astronauts are exposed to lower

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levels of gravity than on earth this

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means that they have less mechanical

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stress put on their bones as they move

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around

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scientists believe that the bones

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naturally try to adapt to this new

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environment by increasing the rate that

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the bone is broken down by the

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osteoclasts meanwhile bone formation

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continues to occur at the same rate as

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it does on earth

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the result is an imbalance in bone

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remodeling which leads to an overall

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decrease in bone mineral density

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while in space astronauts can manage

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with lower bone density but when they

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return their bones are less able to cope

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with earth's gravity this increases the

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risk of fracture and injury scientists

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use many different tests to measure the

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density of the astronauts bones results

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show that the astronauts while in space

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lose bone in a similar pattern to people

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on earth who suffer from osteoporosis

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but the astronauts lose it at a much

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scientists have found that exercise when

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combined with good nutrition and

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increased vitamin d intake is able to

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preserve some of the bone that was

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previously being lost

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since 2008 astronauts have been able to

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use a new exercise machine called the

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advanced resistive exercise device or a

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red it is thought that this increase in

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force triggers the formation of new bone

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bringing more balance to the bone

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remodeling process and allowing the bone

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density to stay at roughly the same

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level as it was before the space flight

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it is a significant achievement to be

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able to maintain bone density in space

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but more experiments need to be carried

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out to see whether the new bone which is

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formed in space has the same structure

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and strength as new bone which is formed

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on earth understanding bone loss

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associated with microgravity may lead to

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better preventive care or therapeutic

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treatments for people on earth suffering

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bone loss as a result of bone diseases