Histology of bones

What is bone made up of?
Bone is a strong, flexible and semi-rigid supporting tissue. It can withstand compression forces, and yet it can bend. Like cartilage, and other types of connective tissue, bone is made up of Cells and Extracellular matrix:

Cells - which in bone are called osteoblasts and osteocytes, (osteo - bone). There are also two other cell types: osteoprogenitor cells and osteoclasts.

Types of bone:

diagram of a bone
The first bone formed at any site is woven (or primary) bone, but this is soon replaced by lamellar bone. In woven bone the collagen fibres are random. In lamellar bone, the collagen fibres have become re-modelled to become more parallel - in layers.

There are two types of mature bone:

1. Compact - which is found in the shafts of long bones (in the diaphyses). This makes up 80% of all bone.

2. Spongy (cancellous) bone - which is found at the ends of long bones (in the epiphysis). This makes up 20% of all bone. This type of bone contains red bone marrow and a network of bony trabeculae.

A 'periosteum' is found on the outside of bone. This is a dense fibrous layer, where muscles insert. It contains bone forming cells. It is not found in the regions of bone covered by articular cartilage.

The endosteum is the name given to the tissue that lines the inner surfaces of bones.