Skeleton

Your skeleton is 206 bones joined together. It has four jobs: support, protection, movement and making blood cells.

Job	How	Example
Support	Holds the body up and gives it its shape	The backbone and leg bones carry your weight
Protection	Hard bone surrounds soft organs	Skull: brain. Ribs: heart and lungs. Vertebrae: spinal cord
Movement	Muscles pull on bones, which move at joints	The biceps pulls the forearm up
Making blood cells	Bone marrow, the soft tissue inside some bones, makes them	Red cells, white cells and platelets

Bones are alive. They have cells, nerves and a blood supply, so they grow and can repair a break. Calcium makes them hard. You get it from foods such as milk, cheese and green vegetables, and vitamin D helps your body take it in.

A joint is where two or more bones meet.

Joint	How it moves	Examples
Hinge	Bends and straightens in one direction, like a door	Knee, elbow, fingers
Ball and socket	In almost every direction, even round in a circle	Hip, shoulder
Fixed	Does not move at all	Between the bones of the skull

Cartilage covers the ends of the bones in a joint: a smooth, tough cushion that stops them rubbing and soaks up shocks. Ligaments hold the bones of a joint together (bone to bone) and are slightly stretchy. Tendons join muscles to bones and do not stretch.

Stretch Joints such as the knee are filled with synovial fluid, which oils them like a hinge. Bones also store minerals such as calcium for the rest of the body. A newborn baby has around 270 to 300 bones; some of them join together as it grows.