Histology of bones Dr Maha ELBeltagy 2018

(osteo= bone, genic= forming). Connective tissue Cells Ground substances 1- Osteogenic (osteo= bone, genic= forming). 2- Osteoblasts (blast= seed). 3-Osteocytes (cyte= cell). 4-Osteoclasts (clast = broken). Fibers Mostly of Calcium and Phosphorus in the form of Hydroxyapatite crystals, responsible about Hardness of bone Collagen

The parts of a long bone Diaphysis-shaft Epiphyses- ends Come together at metaphyses Articular cartilage protects epiphyses Periosteum covers bone Medullary cavity contains marrow; is lined by endosteum

Bone cells

Organization of bone tissue compact spongy

Compact vs. spongy bone Compact bone Spongy bone External layer Arranged in osteons Central canals connected to each other by perforating canals Bones are heavy Found mainly in long bones Spongy bone Near the center No osteons Arranged in trabeculae Major type in short, flat, irregular bones Much lighter than compact bone Supports red bone marrow

Blood and nerve supply to bone Abundant supply of blood May have several nutrient arteries Nerves accompany blood vessels

Ossification (osteogenesis) Bone forms within mesenchyme in layers (intramembranous) Flat bones of skull and mandible Osteocytes secrete calcium Compact and spongy bone form

Endochondral ossification Most bones are formed this way Calcification is triggered when chondrocytes die Vascularization triggers ossification

Bone growth in length (epiphyseal plate) Growth is on epiphyseal side Resting cartilage secures epiphyseal plate Dividing cells are in proliferating cartilage Cells mature in hypertrophic cartilage Osteoblasts replace calcified cartilage

Bones get thicker by appositional growth Osteoblasts form new extracellular matrix Blood vessel becomes enclosed, supports new osteon Osteoblasts lay down extracellular matrix

Bone remodeling replaces old tissue Resorption by osteoclasts, deposition by osteoblasts Strengthens bone Repairs damaged bone