Skeletal Tissues

Human Structure and Development ANHB 2212Week 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

TerminologyGross 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!