Histology of bone Special connective tissue Highly vascularized

Histology of bone • • • Special connective tissue Highly vascularized Mineralized Dynamic Living Hardness Resilience Regenerative capacity

• Plays a role - shape - support - protection - body movement - hematopoiesis - mineral storage

Macroscopic Structure

-Periosteum • Covers external surface of bone • 2 layers-outer fibrous -inner cellular • Functions -Endosteum • Covers the wall of the marrow cavity

Microscopic Structure

Composition Of Bone 1. Intercellular (Matrix) 1. a)Organic 2. Cellular 1. b)Inorganic OSTEOID – Organic part of the bone without inorganic constituent.

1. Bone matrix a) Organic -collagen fibres- type I -ground substance. Chondroitin sulphate b) Inorganic -calcium & phosphate as hydroxyapatite crystals (Ca 10(po 4)6(OH)2) -Magnesium, carbonate, flouride , citrate

2. Bone cells 2. a)Osteogenic cells 2. b)Osteoblasts 2. c)Osteocytes 2. d)Osteoclasts

2. a)Osteogenic cell • Stem cell • Converts to osteoblast • Present on periosteal & endosteal surfaces in adults. • Resembles fibroblast

Osteoblast • Derived from osteogenic cell • Large basophilic cells with eccentric nuclei • Bone forming cell- matrix (organic+inorganic) and fibres • Rich in alkaline phosphatase

Osteocyte • • Mature bone cell Flattened cells with thin cytoplasmic processes Present inside lacunae Maintain patency of canaliculi for diffusion of nutrient

Osteogenic/Osteoprogenitor cell Osteoblast Osteocyte

• • Osteoclast Large multinucleated cells Found at sites called resorption bays/lacunae of Howship Derived from fusion of monocytes of bone marrow Rich in acid phosphatase

Structure of compact bone • • • Havershian system/ Osteon Havershian canal Concentric lamelle Interstitial lamellae Inner circumferential lamellae Outer circumferential lamellae Volkmann’s canal Periosteum Endosteum

Structure of cancellous bone • Haversian system – absent • Thin trabeculae • Large spaces filled with red bone marrow