Osteocytes

• Mature bone cells

• Main cells that perform metabolism

• Do not undergo cell division

Osteoclasts

• -clast= to break

• Huge cells

• Formed from monocytes (WBC)

• Contain lysosomal enzymes

• Destroy bone tissue

• Destruction is called resorption

• Why would bone tissue be destroyed?

Compact Bone Tissue

• Few spaces

• Forms external layer of all bones

• Forms bulk of the body of long bones

• Provides protection and support

• Takes stress

Bone Micro-anatomy (compact)

• Perforating canals (Volkmann’s canals) – a miniature passageway by means of which blood vessels and nerves penetrate the bone

• Central (Haversian) canals – a microscopic tube running the length of the spinal cord containing blood and lymphatic vessels and nerves.

• Concentric lamellae – rings of hard, calcified matrix found in compact bone.

Cont…

• Lacunae –a small, hallow space, such as that found in bones in which the osteocytes lie

• Canaliculi (KA-li-sEz)– small channels in bone, where they connect lacunae

• Osteon – bone tissue

• SEE HAND-OUT TO LABEL THESE!

Spongy Bone Tissue

• Does not contain true osteons

• Trabeculae– = little beams

• Spaces between trabeculae are filled with red bone marrow– Red bone marrow produces blood cells

(hemopoeisis)

• Makes up most of short, flat, and irregular bones

• Makes up most of the epiphyses on long bones

• Skull, hip, ribs, sternum, vertebrae, ends of long bones are typical hemopoetic sites

Ossification: Bone Formation

• This is the process of forming bone• Embryonic skeleton is formed of

hyaline cartilage which must turn to bone

• Osteogenic cells form• Become osteoblasts—secrete• Ossification starts at 6-7th week of

embryonic life• Continues throughout adulthood

Homeostasis of Bone

• Bone must continually renew itself

• Old bone is constantly being destroyed

• New bone is formed in its place

• This is called remodeling– The on going replacement of old bone

with new bone

• Osteoclasts– Responsible for resorption of bone tissue

• Balance must be maintained between removing minerals and depositing minerals (such as calcium)

– Osteoclasts and osteoblasts– Too much= spurs, bumps– Too little= weakens bones, fractures

Nutrients for Bones

• Adequate minerals– Calcium, phosphorus, magnesium

• Vitamins A, C, and D• Several hormones

– Human growth hormone (hGH)– Insulin-like growth factor (IGF)– Giantism vs dwarfism

• Weight-bearing exercise