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Bone histology Muhammed Asif BMLT, M.Sc (medical anatomy) Dept. Of Anatomy YMC. DEFINITION Bone is a dynamic, highly vascular specialized connective tissue, which supports the body and provides leverage for movements. COMPOSITION OF BONE Matrix Cells Organic Inorganic Osteoprogenitor cells Osteoblasts Osteocytes Osteoclasts Lamella Lamella Organic material Inorganic material Matrix Calcium & phosphate • Ground substance Hydroxy – apatite crystals • Collagen MACROSCOPIC STRUCTURE Shaft – Periosteum – Cortex – Medullary cavity: • Red or yellow bone marrow. 2 Ends: – Covered by hyaline cartilage Compact & spongy bone Spongy bones Structure of a Flat Bone • Compact bone forms the outer shell of all bone and also the shafts in long bones. • Spongy bone is found at the expanded parts of long bones and fills most irregular bones. • Spongy or cancellous bone consists of a lattice of thin threads of bone called trabeculae, which are lamellae that are arranged as rods or plates and is less dense than compact bone. Red bone marrow is found between the trabuculae. Bone is covered by………???? Periosteum The external surface of the bone is covered by a connective tissue membrane called periosteum except articular surface. The periosteum consist of outer fibrous layer & inner cellular layer. The periosteum is united to underlying bone by Sharpey’s fibers, but it is stronger where there is attachment of tendons & ligaments. Abundant periosteal arteries nourish outer part of the cortex. It is rich in nerve supply, which makes it more sensitive. MACROSCOPIC STRUCTURE Shaft – Periosteum • Outer fibrous • Inner cellular – Cortex • Compact bone – Medullary cavity: • Red or yellow bone marrow. 2 Ends: – Covered by hyaline cartilage Cortex Lamella Organic material Inorganic material Matrix Calcium & phosphate • Ground substance Hydroxy – apatite crystals • Collagen • Ground substance consist of 25% water and glycosaminoglycans (are of 3 different types i.e, hyaluronic acid, chondrotin sulphate & keratan sulphate) and special glycoproteins (osteonectin & osteocalcin). • 25% Fibers – type 1 collagen fibers synthesized by osteoblasts. • This fiber provide tensile strength & flexibility. • 50% Inorganic material - Calcium & phosphate Provides hardness, resistance to bending and forms about 65% of bone weight. Haversian canal • Contains – – Small amount loose connective tissue – Capillaries nerves and – Lymphatics 21 COMPOSITION OF BONE Matrix Cells Organic Inorganic Osteoprogenitor cells Osteoblasts Osteocytes Osteoclasts Lamella OSTEOPROGENITOR CELLS / OSTEOGENIC CELLS • Stem cells of mesenchymal origin. • Present – endosteum, periosteum & haversian canal • Function - Proliferate and convert themselves into osteoblasts. OSTEOBLASTS • Oval in shape. • Derived – osteogenic cells • Found – wherever there is bone formation • Function Synthesis and secretion of matrix. Calcification of bone matrix. OSTEOCYTES • Derived from osteoblasts. • Mature cell bone cells • Star shaped • Present in lacunae. • Functions: – Play a role in patency of canaliculi for difussion of nutrients OSTEOCLASTS • Large & multinucleated cell • Cytoplasm – lysosomes & mitochondria • Present – sites of bone resorption called pits of howships • Function – helps in bone resorption