Its 206 bones form a rigid framework to which the softer tissues and organs of the body are attached.

Vital organs are protected by the skeletal system. The brain is protected by the surrounding skull as the heart and lungs are encased by the sternum and rib cage.

There are about 60 muscles in the face. Smiling is easier than frowning. It takes 20 muscles to smile and over 40 to frown.

The longest muscle in the body is the sartorius, from the outside of the hip, down and across to the inside of the knee. It twists and pulls the thigh outwards.

The smallest muscle in the body is the stapedius, deep in the ear. It is only 5mm long and thinner than cotton thread. It is involved in hearing.

A person has around 4-5 litres of blood. The blood is the transport system by which oxygen and nutrients reach the body's cells, and waste materials are carried away. In addition, blood carries substances called hormones, which control body processes, and antibodies to fight invading germs. The heart, a muscular orga

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