ARRANGEMENT OF LAMELLAR BONE IN THE DIAPHYSES – 3
The wall of the diaphyses of mature long bones is composed of thousands or millions of very thin bone plates, the bone lamellae. Each lamella is made of calcified extracellular matrix (collagen fibers and other molecules of the matrix). Osteocytes are located within the bone matrix, between the lamellae.
The lamellae of the wall of diaphyses are organized into three main layers:
1 – The external or outer circumferential lamellae (highlighted in red) is a layer that surrounds the diaphysis in form of stacks of parallel layers of slightly curved lamellae.
2 – The thinner internal or inner circumferential lamellae, placed on the inner surface of the diaphysis facing the medullary canal, is composed of stacks of slightly curved parallel lamellae (highlighted in green).
3 – The middle layer is the thickest (highlighted in blue). It contains numerous Haversian systems as well as interstitial lamellae, differently sized slightly curved parallel lamellae placed between the Haversian systems.
The lamellae of the wall of diaphyses are organized into three main layers:
1 – The external or outer circumferential lamellae (highlighted in red) is a layer that surrounds the diaphysis in form of stacks of parallel layers of slightly curved lamellae.
2 – The thinner internal or inner circumferential lamellae, placed on the inner surface of the diaphysis facing the medullary canal, is composed of stacks of slightly curved parallel lamellae (highlighted in green).
3 – The middle layer is the thickest (highlighted in blue). It contains numerous Haversian systems as well as interstitial lamellae, differently sized slightly curved parallel lamellae placed between the Haversian systems.
Except at the articular surfaces, the internal and external surfaces of bones are covered by connective tissue cell layers called endosteum and periosteum, respectively (both not visible in the figure).
These layers are formed by bone lining cells (osteoprogenitors and active and inactive osteoblasts).
The endosteum, is usually a thin layer that covers the internal surface of the bone and that stays in direct contact with the contents of the medullary cavity. The thicker periosteum is made of connective tissue proper, placed over the osteoprogenitors and osteoblasts.
