Skeletal System Bone Structure

Parts of the Bone

Bone is made up of minerals and is hard in some places but soft in others. A bone in a living organism consists of both living tissue and non-living substances. In living bone there are blood vessels, nerves, collagen, and living cells. First, in the periosteum (tissue around bones) there's a bony layer called compact bone (also called cortical bone) which is solid, strong, and resistant to bending. This is all inside the part of the bone called the diaphysis (long part of bone). Underneath the periosteum is the center of the bone known as the medullary (marrow) cavity that is filled with red and yellow bone marrow. Yellow is mainly fatty tissue, while red is where the majority of blood cells are produced. Next you have the area between the diaphysis and epiphysis at both ends of the bones called the metaphysis. The metaphysis is a layer of firm but elastic type of cartilage that provides shock absorption to the joint. Then is the epiphysis (end of a long bone). This is made up largely of spongy or cancellous bone, which provides the greatest amount of elastic strength since the epiphysis is shown to the greatest forces of compression. Lastly, you have the epiphyseal plates which are just plates of cartilage. These are also known as growth plates because they let the long bones grow to their length during childhood. When we stop growing, the cartilage plates stop making cartilage cells and are slowly replaced by actual bone.