Anatomy and histology of bone

Anatomy and histology of bone by Dr Bipul Borthakur

1. ANATOMY AND HISTOLOGY OF BONE PROFESSOR & HOD, DEPTT OF ORTHOPAEDICS, SILCHAR MEDICAL COLLEGE AND HOSPITAL

2. FUNCTION OF BONE Serves as attachment sites for muscles. Protection of organs( eg cranium,ribs and pelvis). Acts as reservoir for mineral in the body 99% calcium stored as hydroxyapatite crystals.

3. BONE FORMS LONG BONES Formed by enchondral ossification. Primary in shaft and and sec. growth centers FLAT BONES Formed by intramembranous ossification. eg pelvis,scapula .

4. PARTS OF LONG BONESs DIAPHYSIS- Shaft,made of thick cortical bone,filled with bone marrow. METAPHYSIS –Widening of bone near the end made of cancellous bone. EPIPHYSIS –End ( usuallyarticular ) of bone,forms from secondary ossification centers .

5. MICROSCOPIC BONE TYPES WOVEN - Immature or pathologic bone, poorly organised not stress oriented. eg bones in infants , fracture callus and pathological tumours.

6. LAMELLAR TYPES Mature bone highly organised with stress orientation. Mature cortical and cancellous bone are made of lamellar bones.

7. STRUCTURES OF CORTICAL BONES Strong dense bone,constitute 80% of skeleton. Composed of multiple osteons. Osteons are made up of concentric bone lamellae with a central canal( haversian canal) containing osteoblasts.

8. Lamellae are connected by canaliculi , cement lines mark outer limit of osteon, cortical bone is found in diaphysis of long bones. Volkmann′s canals – radially oriented , have arteriole and connect adjacent osteons.

9. STRUCTURE OF CANCELLOUS BONE Crossed lattice structure,makes upto 20% of the skeleton. High bone turnover rate,bone is resorbed by osteoclasts in howship lacunae and formed on the opposite side of trabeculae . Osteoporosis is common and found in vertebral bodies,femoral neck,distal radius , tibial plateau and found in metaphysis and epiphysis.

10. BONE COMPOSITION Inorganic phase – 1)calcium hydroxyapatite. 2) Osteocalcium phosphate. Organic phase 1)collagen 2)Proteoglycans

11. 3)Non collagenous proteins. 4)Cells Water approx. 5 % of bone weight. Periosteum surrounds the bone and is thicker in children,responsible for growing diameter. .

12. INORGANIC PHASE Approx 60% of body weight. Ca10(po4)6(OH)2 is primary mineral in bone. Adds compressive strength . Brushite is secondary mineral in bone.

13. ORGANIC PHASE Collagen Known as osteoid before its mineralization Approx 35% of bone weight. Type 1 collagen gives tensile strength. Proteoglycans – Hyaluronic backbone with multiple glycosaminoglycans . gives compressive strength.

14. Non collagenous protein- Osteocalcin is indicator of bone turnover rate. eg Pagets disease. osteonectin and osteopontin . Cells include osteoblasts,osteocytes and osteoclasts.

15. OSTEOBLASTS Produce bone matrix ,makes type 1 collagen. Follow osteoclasts in cutting cones. Receptors –PTH ,vitamin D,glucosteroids estrogens,PGs .

16. OSTEOCYTES AND OSTEOCLASTS Osteoblast surrounded by bone matrix cons 90% of bone cells. Preserves bone,long cell process communicate via canaliculi receptors include PTH and calcitonin . Osteoclast are large multinucleated derived from monocytes and macrophages absorbs bone and found in howship lacunae.