Functions of the skeletal system:
1.Protection - the cranium and ribs protect the brain and vital organs in the chest.
2.Shape - gives shape to the body and makes you tall or short.
3.Support - holds your vital organs in place when playing sport. The vertebral column holds the body upright.
4.Movement - muscle are attached to bones, which are jointed. When the muscles contract the bones move.
5.Blood production - red blood cells (to carry oxygen) and white blood cells (to protect against infection) are produced in the bone marrow of some bones.

Movement
Abduction:Movement away from the mid-line of the body
Adduction:Movement towards the mid-line of the body
Extension:Straightening limbs at a joint
Flexion:Bending the limbs at a joint.
Rotation:A circular movement around a fixed point

Synovial joints
Cartilage reduces friction. Acts as a shock absorber.
Synovial fluid lubricates the joint.
Synovial membrane produces synovial fluid.
Tendon joins muscle to bone enabling movement.
Ligament joins bone to bone, stabilising the joint.

Osteoporosis:
a medical condition in which the bones become brittle and fragile from loss of tissue, typically as a result of hormonal changes, or deficiency of calcium or vitamin D.