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11.8: Keeping Bones and Joints Healthy

Difficulty Level: At Grade Created by: CK-12
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Why drink milk?

Milk is naturally a good source of calcium. Vitamin D is also often added to milk. Both these nutrients help build strong bones.

Keeping Bones and Joints Healthy

You can help keep your bones and skeletal system healthy by eating well and getting enough exercise. Weight-bearing exercises help keep bones strong. Weight-bearing exercises work against gravity. Such activities include basketball, tennis, gymnastics, karate, running, and walking. When the body is exercised regularly by performing weight-bearing activity, bones respond by adding more bone cells to increase their bone density.

Eating Well

Did you know that what you eat as a teenager can affect how healthy your skeletal system will be in 30, 40, and even 50 years? Calcium and vitamin D are two of the most important nutrients for a healthy skeletal system. Your bones need calcium to grow properly. If you do not get enough calcium in your diet as a teenager, your bones may become weak and break easily later in life.

Osteoporosis is a disease in which bones lose mass and become more fragile than they should be. Osteoporosis also makes bones more likely to break. Two of the easiest ways to prevent osteoporosis are eating a healthy diet that has the right amount of calcium and vitamin D, and to do some sort of weight-bearing exercise every day. Foods that are a good source of calcium include milk, yogurt, and cheese. Non-dairy sources of calcium include Chinese cabbage, kale, and broccoli. Many fruit juices, fruit drinks, tofu, and cereals have calcium added to them. It is recommended that teenagers get 1300 mg of calcium every day. For example, one cup of milk provides about 300 mg of calcium, or about 30% of the daily requirement. Other sources of calcium are shown in Figure below.

There are many different sources of calcium. Getting enough calcium in your daily diet is important for good bone health.

Vitamin D is unusual since you don't have to rely on your diet alone to get enough of this vitamin. Your skin makes vitamin D when exposed to sunlight. Pigments in the skin act like a filter that can prevent the skin from making vitamin D. As a result, people with darker skin need more time in the sun than people with lighter skin to make the same amount of vitamin D.

You can also get vitamin D from foods. Fish is naturally rich in vitamin D. Vitamin D is added to other foods, including milk, soy milk, and breakfast cereals. Teenagers are recommended to get 5 micrograms (200 IU) of vitamin D every day. A 3½-ounce portion of cooked salmon provides 360 IU of vitamin D.

Bone Fractures

Even though they are very strong, bones can fracture, or break. Fractures can happen at different places on a bone. They are usually caused by excess bending stress on the bone. Bending stress is what causes a pencil to break if you bend it too far.

Soon after a fracture, the body begins to repair the break. The area becomes swollen and sore. Within a few days bone cells travel to the break site and begin to rebuild the bone. It takes about two to three months before compact and spongy bone form at the break site. Sometimes the body needs extra help in repairing a broken bone. In such a case a surgeon will piece a broken bone together with metal pins. Moving the broken pieces together will help keep the bone from moving, and give the body a chance to repair the break. A broken ulna has been repaired with pins in Figure below.

The upper part of the ulna, just above the elbow joint, is broken, as you can see in the X-ray to the left. The x-ray to the right was taken after a surgeon inserted a system of pins and wires across the fracture to bring the two pieces of the ulna into close proximity.

Cartilage Injuries

Osteoarthritis occurs when the cartilage at the ends of the bones breaks down. The break down of the cartilage leads to pain and stiffness in the joint. Decreased movement of the joint because of the pain may lead to weakening of the muscles that normally move the joint, and the ligaments surrounding the joint may become looser. Osteoarthritis is the most common form of arthritis. It has many contributing factors, including aging, sport injuries, fractures, and obesity.

Ligament Injuries

Recall that a ligament is a short band of tough connective tissue that connects bones together to form a joint. Ligaments can get injured when a joint gets twisted or bends too far. The protein fibers that make up a ligament can get strained or torn, causing swelling and pain. Injuries to ligaments are called sprains. Ankle sprains are a common type of sprain.

Preventing Injuries

Preventing injuries to your bones and ligaments is easier and much less painful than treating an injury. Wearing the correct safety equipment when performing activities that require such equipment can help prevent many common injuries. For example, wearing a bicycle helmet can help prevent a skull injury if you fall. Warming up and cooling down properly can help prevent ligament and muscle injuries. Stretching before and after activity also helps prevent injuries.


  • calcium:
  • fracture: A break in bone.
  • osteoarthritis: A condition in which cartilage breaks down in joints, causing stiffness and pain.
  • osteoporosis: A disease in which bones become more fragile and likely to break.
  • sprains: Injuries to ligaments where a joint is put through a range of motion greater than its normal range.
  • vitamin D:


  • You can keep your bones healthy through weight-bearing exercises and getting enough calcium and vitamin D in your diet.
  • Possible problems of the skeletal system include osteoporosis, osteoarthritis, fractures, and sprains.


Use the resource below to answer the questions that follow.

  1. How much calcium does the average person need per day? What are good sources of calcium? What vitamin helps you process calcium?
  2. How do weight bearing exercises help your bones?
  3. How can table salt (NaCl) be bad for your bones?


  1. What are two good habits to keep your skeletal system healthy?
  2. What is osteoarthritis?

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arthritis Inflammation of a joint causing pain and swelling.
calcium Element that is a component of bone; a necessary element in nerve conduction, heartbeat, muscle contraction, and many other physiological functions.
fracture Break in bone.
ligament Short band of tough connective tissue that connects bones together to form a joint.
osteoarthritis Condition in which cartilage breaks down in joints, causing stiffness and pain.
osteoporosis Disease in which bones become more fragile and likely to break.
sprains Injuries to ligaments where a joint is put through a range of motion greater than its normal range.
vitamin D Any of a group of sterols necessary for normal bone growth; found in milk, fish, and eggs and can be produced in the skin on exposure to sunlight.

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Difficulty Level:
At Grade
7 , 8
Date Created:
Nov 29, 2012
Last Modified:
Aug 30, 2016
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