Skeletal Tissues Human Structure and Development ANHB 2212

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!