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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