SKELETON

WHAT'S A SKELETON?

• All the bones in the human body together are called the skeleton. The skeleton provides strength to our body so we don't just flop around like jellyfish. We have 206 bones in our body. Each bone has a function. Some bones offer protection to softer more fragile parts of body. For example, the skull protects the brain and the rib cage protects our heart and lungs. Other bones, like bones in our legs and arms, help us to move around by providing support for our muscles.

WHAT ARE BONES MADE OF?

• Around 70 percent of your bones are not living tissue, but hard minerals like calcium. The outside of the bone is called the cortical bone. It's hard, smooth, and solid. Inside the cortical bone is a porous, spongy bone material called the trabecular or concellous bone. This bone is lighter allowing for the bone itself to be lighter and easier for us to move around. It also allows room for blood vessels and makes our bones slightly bendable. This way our bones won't break so easily. At the center of bones is a softer substance called marrow

BONE MARROW

• There are two types of bone marrow, yellow and red. Yellow bone marrow is mostly fat cells. Red marrow is important because this is where our body produces red and white blood cells. When we are born, all of our bones have red marrow. By the time we are adults about half of our bones have red marrow.

BONE

Joints

• Our bones come together and connect at special places called joints. Your knees and elbows are joints, for example. Many joints have a large range of movement and are called ball and socket joints. The shoulder and hip are ball and socket joints. Joints have a smooth, durable material called cartilage. Cartilage, together with fluid, allows bones to rub against each other smoothly and not wear out.