Cartilage and Os: Types of mature os

Compact Bone

osteon diagram TS

The diagram above shows a transverse view of an osteon (Haversian system) - the basic unit of compact os.

diagram of haversian canal

The diagram above shows a longitudinal view of an osteon.

Some, generally older, compact bone is remodelled to form these Haversian systems (or osteons). The osteocytes sit in their lacunae in concentric rings around a cardinal Haversian culvert (which runs longitudinally). The osteocytes are arranged in concentric rings of bone matrix called lamellae (trivial plates), and their processes run in interconnecting canaliculi. The central Haversian canal, and horizontal canals (perforating/Volkmann's) canals comprise blood vessels and nerves from the periosteum.

This photo shows a cross section through os. Can you identify the primary and secondary Haversian systems, fundamental canals and os lamellae?

This is a high power photograph of a unmarried Haversian system. Can you place the concentric lamellae, central culvert and the lacunae. Because of the way the bone is prepared for sectioning, you cannot see the osteocytes in the lacunae, only the spaces left behind. The alternating bright and dark concentric rings (lamellae) are due to an alternating organisation of collagen fibres in the bone matrix. The collagen fibres in each layer are parallel to each other, only at right angles to the fibres in the alternate layers on either side. (Recall about how this will impact the bones ability to resist tensile stress).

Cancellous Bone

This photograph shows a department through a marrow space inside a bone. Can you identify the os marrow, trabeculae, osteocytes, and some adipocytes, that are in the bone marrow.

Cancellous bone has large open spaces (marrow spaces) and plates of bone called trabeculae.