Osteocytes
• Mature bone cells
• Main cells that perform metabolism
• Do not undergo cell division
Osteoclasts
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-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
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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
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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
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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