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=Bone up on Bones= Take a look at your bones. Did you know you have 206 total bones in your body? The following sections will help you understand the functions of bones and how space travel affects them. Don't take the quiz until you get all the facts!

Bare Bone Facts
Think about why your skeleton is important to you. Some of the skeleton's major functions are:
 * Support
 * Protection
 * Mineral storage

Support
Bones bear the weight of the body and work with muscles to hold it upright. You would be a messy puddle of skin without your bones to support you.

Protection
Bones shield the delicate internal organs and the spinal cord. Your skull is like a helmet for your brain. Your spine surrounds many nerves. Your ribs are armor for your heart and lungs.

Mineral Storage
Bones store minerals for your body. 99% of the calcium in your body is stored in bones! Bones need calcium in order to be strong. Muscles and nerves also depend on calcium to function properly. Blood carries calcium throughout your body and delivers it where it is needed.

Bones and muscles work together to move you.
Joints are places where two bones come together. There are 68 joints in your body! What joints would need to work properly if you stood up right now? The main joints would be your knee, hip, and ankle. The bones don't direct the motion, however; they rely on muscles. When muscles contract, the force is transmitted from muscles to bones through tendons.

How many bones do you have?
When you were born, you had 270 bones. Some of those bones fuse (connect and solidify) to form the adult skeleton containing 206 main bones. The last bones fuse around age 20! There are also tiny, uncounted bones in the tendons of your thumb, big toe, and other pressure points. Did you know that your hands contain 19 bones each?

Bones in Space
Microgravity experienced during space flight causes loss of some bones' density. Bone density is a measure of how solid and strong your bones are on the inside. Decreases in bone density can cause increased calcium in the blood, which can contribute to painful and harmful kidney stones. Osteoporosis, a bone thinning disease, weakens bones and increases their risk of fracture. Astronauts show symptoms similar to osteoporosis, or porous bone, after periods of time in space. Like osteoporosis on Earth, the weight-bearing bones of astronauts on long missions are left weak and less able to support the body's weight. When astronauts return to Earth, their risk of fracture increases.

Weight-bearing bones
Astronauts lose bone mass from bones in their pelvis, lower legs, and lower spine. Why do you think these bones become weaker in space? These bones are used to support your weight on Earth. They grow strong when they are exercised because they work against gravity to hold you up. Because there is very little gravity in space, the bones don't have to support astronauts' weight. Therefore, weight-bearing bones don't stay as strong as they do when they're exercised on Earth. Since loss of bone density begins within the first few days in space, we need to figure out how to keep astronauts' bones strong. What do you do to help your bones? Do you exercise? Drink milk or eat foods high in calcium? Take a vitamin? Wear helmets and knee pads when you ride a bike or skateboard? Did you know that some astronauts lose up to 12% of their weight-bearing bone mass on the space station? The spine, hip and leg bones lose an average of about 1% of their mass each month. They regain most of their bone mass in the months following their return from space, but not all of it.

Think about these questions and make a mental hypothesis:

 * How might loss of bone mass affect plans for long-term space travel?
 * How might we, here on Earth, benefit from microgravity research into bone density loss?
 * How can you keep your bones healthy?

How might loss of bone mass affect plans for long-term space travel?
We may have to limit spaceflight if:
 * it harms astronauts during long stays in space,
 * it harms astronauts on return to Earth, or
 * it quickens the aging process of bones

How might we, here on Earth, benefit from microgravity research into bone density loss?
Loss of bone density in space is a lot like osteoporosis. Solving the problem in space could certainly help many people back here on Earth. We are also learning more about how to keep our bones healthy on Earth.

How can you keep your bones healthy?

 * Make sure you eat food with lots of calcium. Dairy products, like milk, cheese and yogurt, are especially high in calcium!
 * Exercise your weight-bearing bones several times a week:
 * dance
 * play soccer
 * play tennis
 * hike
 * play basketball
 * jump rope