Joints and Movement
Senior 2 · Biology
Joints and Movement
Lesson 3 of 3
20 min
Let's begin
Many Rwandans carry heavy loads on their heads and backs, bend over hoes in the fields for hours, or sit hunched over desks and phones. Footballers twist ankles and knees, and older people often suffer painful joints. Healthy habits built now protect your bones and joints for the rest of your life.
Worked example
A student breaks a leg and wears a plaster cast for six weeks. When the cast comes off, the bones of that leg are thinner and lighter than before, and the leg muscles are weaker. Why? Bone is constantly being rebuilt. Bone-building cells add new bone and other cells remove old bone, and the balance depends on how much stress the bone carries. A leg that bears no weight loses more bone than it gains. Once the student walks and exercises again, the bone rebuilds.
The lesson for everyone: bones that are used become stronger. Bone keeps growing until about age 25, so the teenage years are when you build most of the bone you will have as an adult.
| Condition | What it is | Prevention or first aid |
|---|---|---|
| Sprain | a ligament is over-stretched or torn, often at the ankle or knee | first aid RICE: Rest, Ice, Compression (a firm bandage), Elevation (raise the limb) |
| Dislocation | a bone is forced out of its joint, often at the shoulder | keep it still and get medical help; never force it back yourself |
| Fracture | a broken bone | keep the limb still with a splint and get medical help; a broken bone takes about two months to join firmly |
| Arthritis | painful, stiff, swollen joints. In osteoarthritis the articular cartilage wears away so bone rubs on bone; rheumatoid arthritis is caused by the body's immune system attacking the joints | keep a healthy weight; stay active; avoid joint injuries |
| Osteoporosis | bones lose mass and become brittle, so they break easily; common in older people, especially women | calcium, vitamin D and weight-bearing exercise, especially while young |
| Rickets | soft, weak bones that bend (for example bow legs) in children lacking vitamin D or calcium | sunlight and a diet with enough calcium and vitamin D |
| Gout | crystals of uric acid collect in a joint, often the big toe, causing sudden pain | medical treatment; limit alcohol and very rich foods |
Worked example
During a netball match a player lands awkwardly. Her ankle swells and hurts, but she can still move her toes, and an X-ray shows no broken bone. What is the likely injury and the first aid? A sprain: the ligaments of the ankle have been over-stretched or torn. Apply RICE: rest the ankle, put ice wrapped in a cloth on it, wrap it firmly in a bandage, and keep it raised.
Tip
Strong bones = calcium + vitamin D + exercise. Sprains = RICE. Lifting = use your legs, not your back.
Match each disorder to the tissue it affects: sprain → ligament; arthritis → cartilage; fracture, osteoporosis and rickets → bone.
Explain why vitamin D is needed for healthy bones, and state how the body can get it.
Solution: Vitamin D allows calcium to be absorbed from food in the gut, and calcium hardens bone. The skin makes vitamin D in sunlight; eggs and fish also provide it.
Give two habits that reduce the risk of back injury when carrying heavy loads.
Solution: Any two of: bend the knees and keep the back straight; hold the load close to the body; lift by straightening the legs; do not twist while lifting; share very heavy loads; carry bags on both shoulders.
What is the difference between a sprain and a dislocation?
Solution: In a sprain a ligament is over-stretched or torn, but the bones stay in place. In a dislocation a bone is forced out of its joint.
Why does osteoarthritis make movement painful?
Solution: The articular cartilage wears away, so the ends of the bones rub directly against each other, causing friction, pain and stiffness.
Remember
Sources and credits
