Skeletal Tissues Human Structure and Development ANHB 2212 Week 11 – 2006 Avinash Bharadwaj

Specialised Connective Tissue Better resistance to forces in various directions Arrangement of fibres Ground substance Additional elements – mineral Cartilage –Resists compression (Compare fibrous tissue) –Firm Bone –Resists compression and shearing forces –Hard, mineralised –Limitations on cell metabolism  vascularity

Tissue Vs Organ Bone as a tissue –Matrix – fibres, ground substance, calcium compounds as crystals –Cells – osteocytes, osteoblasts, osteoclasts –Blood vessels –Periosteum Named bones as organs –Shell of bony tissue –Bone marrow Red – blood forming White (yellow) – adipose

Terminology Gross anatomical Types –Long –Short –Flat –Irregular Parts (long bones) –Shaft (diaphysis) –Epiphysis –Metaphysis Appearance –Compact –Cancellous (trabecular / spongy)

Bone as a Connective Tissue Bone forming cell – osteoblast. Produces matrix around itself. Calcium deposition – enzyme mediated. Orderly deposition of microcrystals. –Similar to calcium hydroxyapatite. Ossification is not the same as calcification! Hard matrix  lacuna. Osteocytes – resting cells, maintenance. Must never be too far from a blood vessel.

And more… Bone just before mineralisation – osteoid. Newly formed bone –Irregular arrangement of collagen –Woven bone (Not to be confused with ‘cancellous’) Mature bone (lamellar bone) –Sheets of matrix (lamellae) –Collagen fibres in a sheet – roughly parallel –Neighbouring sheets – different directions Compact bone, as seen in a t.s. of a long bone, is illustrative.

Structure of Compact Bone Mechanical principles –Tube versus column Economy and strength –Multiple units Built around blood supply –Shearing forces – both directions Alternate layers Direction of collagen fibres

Terminology Again! Periosteum and endosteum Outer circumferential lamellae Inner circumferential lamellae Osteons ( Haversian systems ) –Haversian lamellae –Haversian canals –Transverse canals (Volkmann’s) Bone structure is built around blood vessels. Cancellous bone is also lamellar!

Woven Lamellar

The Cells of Bone Osteoblast –Large cells, basophilic cytoplasm and large nuclei… (More later). Osteocyte –Lacuna –Canaliculi – comunications between lacunae –Osteocyte processes in canaliculi Osteoclast (“bone-breaker”) –Phagocytic –Giant multinucleated cells

Bone – A Dynamic Tissue! Growth – over a limited period. Repair and maintenance. Remodelling –During growth period –After injury and repair –In response to forces Dynamic calcium reservoir –Hormonal control Osteoclasts (“bone-breakers”) are equally important!