Bone Tissue

Bone Tissue

1. Periosteum

   • The periosteum is a fibro-collagenous layer at the outermost layer of the bone. It is anchored by Sharpey’s fibres (collagen fibres) and found along the outer surface with the exception of the articular surfaces of the bone and areas of ligament and tendon insertion. The periosteum is actively involved in the repair of fractures.

2. Endosteum

   • The osteoblasts at the endosteum are flat and are surrounded by type III collagen. It extends along the inner surface of the bone; projecting even into the Haversian canals.

3. Osteoclasts

   • Osteoclasts are thought to be monocyte derivatives that have the responsibility of removing bone during growth and remodelling. They are commonly found in Howship’s lacunae (resorption bays). Owing to the high metabolic demand of these cells, there are numerous mitochondria in the cytoplasm.

4. Osteoblasts

   • Unlike the osteoclasts, osteoblasts are mononuclear, cuboidal and basophilic cells that are found on the developing surface of bone during growth or remodelling. Osteoblasts secrete and also facilitate the mineralization of osteoid matrix.

5. Osteocytes

   • Osteoblasts become trapped in the bone matrix that they produce. Subsequently, they differentiate into osteocytes. These cells retain the cytoplasmic projections and form numerous communications with neighbouring osteocytes and osteoblasts

6. COMPACT

   • Compact bone stands in stark contrast to trabecular bone in several ways. The functional units of compact bone are osteons; which contain a centrally located Haversian canal, encased in lamellae (concentric rings). Osteocytes can be observed in the lacunae between the osteons.

7. SPONGY

   • Histologically, spongy bone is comprised of anastomosing strips of slender bone known as trabeculae that enclose marrow and blood vessels. It forms the relatively softer core of the bones that is filled with marrow.