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 6-7 th 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