ARRANGEMENT OF LAMELLAR BONE IN THE DIAPHYSES – 3
The wall of the diaphysis of mature bones is formed by thousands or millions of very thin bone plates, the bone lamellae. They are made of calcified collagen fibers plus other components of extracellular matrix. Osteocytes are placed between the lamellae.
The wall is composed by three layers of lamellae.
1 – The external or outer circumferential lamellae (highlighted in red) surround the diaphysis as several layers of stacks of curved parallel lamellae.
2 – The thin inner border of the diaphysis, facing the medullary canal, is composed by internal or inner circumferential lamellae, stacks of curved parallel lamellae (highlighted in green).
3 – The widest layer is the middle one (highlighted in blue). It contains Haversian systems and interstitial lamellae, stacks of differently sized lamellae placed between Haversian systems.
The wall is composed by three layers of lamellae.
1 – The external or outer circumferential lamellae (highlighted in red) surround the diaphysis as several layers of stacks of curved parallel lamellae.
2 – The thin inner border of the diaphysis, facing the medullary canal, is composed by internal or inner circumferential lamellae, stacks of curved parallel lamellae (highlighted in green).
3 – The widest layer is the middle one (highlighted in blue). It contains Haversian systems and interstitial lamellae, stacks of differently sized lamellae placed between Haversian systems.
Excepting the articular surfaces, all internal and external surfaces of bones are covered by cell layers called respectively endosteum and periosteum (not visible in the figure). These layers are formed by bone lining cells (osteoprogenitors plus active and inactive osteoblasts).
The endosteum, usually a thin layer, stays in direct contact with the content of medullary cavity. The thicker periosteum is made of connective tissue proper placed over the osteoprogenitors and osteoblasts.
