Answer:
Bones are made up of two types of bone tissues:
Compact bone is the solid, hard outside part of the bone. It looks like ivory and is extremely strong. Holes and channels run through it, carrying blood vessels and nerves.
Cancellous (pronounced: KAN-suh-lus) bone, which looks like a sponge, is inside compact bone. It is made up of a mesh-like network of tiny pieces of bone called trabeculae (pronounced: truh-BEH-kyoo-lee). This is where bone marrow is found.
In this soft bone is where most of the body's blood cells are made. The bone marrow contains stem cells, which produce the body's red blood cells and platelets, and some types of white blood cells. Red blood cells carry oxygen to the body's tissues, and platelets help with blood clotting when someone has a cut or wound. White blood cells help the body fight infection.
Bones are fastened to other bones by long, fibrous straps called ligaments (pronounced: LIG-uh-mentz). Cartilage (pronounced: KAR-tul-ij), a flexible, rubbery substance in our joints, supports bones and protects them where they rub against each other.
How Do Bones Grow?
The bones of kids and young teens are smaller than those of adults and contain "growing zones" called growth plates. These plates consist of multiplying cartilage cells that grow in length, and then change into hard, mineralized bone. These growth plates are easy to spot on an X-ray. Because girls mature at an earlier age than boys, their growth plates change into hard bone at an earlier age.
Bone-building continues throughout life, as a body constantly renews and reshapes the bones' living tissue. Bone contains three types of cells:
osteoblasts (pronounced: AHS-tee-uh-blastz), which make new bone and help repair damage
osteocytes (pronounced: AHS-tee-o-sites), mature bone cells which help continue new born formation
osteoclasts (pronounced: AHS-tee-o-klasts), which break down bone and help to sculpt and shape it
