In Cells, Tissues, Organs and Systems you saw cells build tissues, tissues build organs, and organs work together as organ systems. The first system to meet is the frame that holds the rest of you up.
Key idea
The skeleton has four jobs: it supports the body, protects organs (the skull guards the brain, the ribs guard the heart and lungs), works with muscles to let you move, and makes blood cells in the marrow inside many bones. An adult skeleton usually has 206 bones.
Why it works
Bone is a living organ. It has bone cells, blood vessels and nerves, and it stores calcium the body can draw on. Bone cells keep removing old bone and building new bone. That is how bones grow longer in children, get stronger with use, and knit back together after a break, usually with a cast or splint holding the pieces still.
Worked example: Match the job
Which job does each bone mainly do? (a) the skull (b) the femur, the thigh bone (c) the ribs
- The skull surrounds the brain: protection.
- The femur holds up your weight and is pulled by thigh muscles when you walk: support and movement.
- The ribs wrap the heart and lungs: protection (and they move when you breathe).
Answer: (a) protection (b) support and movement (c) protection.
Worked example: Where blood cells come from
A doctor studies red marrow. What is it making?
- Red marrow is the soft tissue inside many bones, such as the hips and ribs.
- It makes red blood cells, white blood cells and platelets.
Answer: Blood cells.
Common mistake
Students think bones are dead, dry sticks, like the white skeletons in a museum. Those are only the mineral part left behind. In a living body bones are alive: they grow, repair themselves after breaks, and make blood cells.
Babies are born with more separate bone pieces than adults. Many of them fuse together as a child grows, which is part of why the adult count is 206.