1. 19 Sept. 2012Bone_tissue.ppt1

2. 19 Sept. 2012Bone_tissue.ppt2 BONES and SKELETAL TISSUES Skeletal System: a framework, foundation for body & solid support for soft organs

3. 19 Sept. 2012Bone_tissue.ppt3 Skeletal System FUNCTIONS in order evolved –1. PROTECTION –2. LOCOMOTION –3. SUPPORT –4. STORAGE –5. PRODUCTION

4. 19 Sept. 2012Bone_tissue.ppt4 Skeletal tissues Hyaline cartilage Fibrocartilage Elastic cartilage Bone tissue

5. 19 Sept. 2012Bone_tissue.ppt5 Structure of Bone Tissue Bone as connective tissue –Cells, osteocytes, separated by extracellular matrix –Collagen fibers, provide tensile strength –Extracellular matrix solid mineral salts (Calcium phosphate) –“hydroxyapatite” Provides hardness, resistance to bending about 65% of bone weight

6. 19 Sept. 2012Bone_tissue.ppt6 Structure of Bone Tissue Compact bone Spongy bone

7. 19 Sept. 2012Bone_tissue.ppt7 Structure of Bone Tissue Compact bone –Hard, densely calcified “typical bone” –Living tissue with blood supply, nerves –Organized of osteons

8. 19 Sept. 2012Bone_tissue.ppt8 Structure of Bone Tissue Compact bone –Osteon Central (Haversian) canal at center Osteocytes in lacunae surrounding Haversian canal Lamellae of bone matrix between rings of osteocytes

9. 19 Sept. 2012Bone_tissue.ppt9 Structure of Compact Bone –Osteons can’t fit together Interstitial lamellae fill space to make solid structure Circumferential lamellae fill space to shape outer surface of bone

10. 19 Sept. 2012Bone_tissue.ppt10 Structure of Spongy Bone Spongy bone –Trabeculae Irregular thin plates & struts of hydroxyapatite with osteocytes –Spaces between filled with marrow (yellow or red)

11. Formation of Bone: Ossification Two mechanisms –Intramembranous ossification –Endochondral ossification No difference in final result. 19 Sept. 2012Bone_tissue.ppt11

12. 19 Sept. 2012Bone_tissue.ppt12 Intramembranous ossification Begins in embryonic mesenchyme membranes Mesenchyme cells become osteoblasts Begin laying down matrix (osteoid)

13. 19 Sept. 2012Bone_tissue.ppt13 Intramembranous ossification Layer of “woven bone” and periosteum Remodeling to form compact bone on surfaces Cranial & facial bones, mandible, clavicles.

14. 19 Sept. 2012Bone_tissue.ppt14 Endochondral ossification Embryonic mesenchyme differentiates to cartilage –Chondrocytes –Perichondrium “Cartilage model” is starting point for endochondral ossification –(endo- = within, chondr- = cartilage)

15. 19 Sept. 2012Bone_tissue.ppt15 Endochondral ossification Perichondrium becomes periosteum Mesenchyme cells become osteoblasts –Form primary ossification center Cartilage under bone collar calcifies & dies

16. 19 Sept. 2012Bone_tissue.ppt16 Endochondral ossification Invasion of nutrient blood vessel, Continued deterioration of cartilage, Formation of spongy bone

17. 19 Sept. 2012Bone_tissue.ppt17 Endochondral ossification Primary ossification center grows, elongates, Formation of marrow cavity, Formation of secondary ossification centers at ends, Ossification of epiphyses.

18. 19 Sept. 2012Bone_tissue.ppt18 Postnatal bone growth Growth in length at epiphyseal plates –Growth of cartilage –Bone tissue “races” to keep up Growth in width at periosteum –Dismantling and remodeling

19. 19 Sept. 2012Bone_tissue.ppt19 Parts of a long bone

20. Bone cells 19 Sept. 2012Bone_tissue.ppt20 Osteoprogenitor cells Osteoblasts –Bone forming cells –Lay down new bone matrix (osteoid) Osteocytes –Mature bone cells –Isolated in lacunae Osteoclasts –Dismantle old bone matrix –Release Ca 2+ and phosphate

21. 19 Sept. 2012Bone_tissue.ppt21 Remodeling Normal continuous process –Osteoclasts dismantle old matrix –Osteoblasts rebuild bone matrix Allows –Maintenance of bone tissue –Change in shape with age & weight –Reinforcing of parts subject to stress & strain

22. 19 Sept. 2012Bone_tissue.ppt22 Remodeling & Ca 2+ Depends on –Homeostasis of Ca 2+ and phosphate –Low Ca 2+ Parathyroid hormone (PTH) stimulates osteoclast activity Calcitriol & Vitamin D s timulate absorption of Ca 2+ from intestine.

23. 19 Sept. 2012Bone_tissue.ppt23 Remodeling & Ca 2+ Depends on –Homeostasis of Ca 2+ and phosphate –High Ca 2+ Calcitonin s timulates deposition of Ca 2+ into bone tissue. Excess Ca 2+ excreted.

24. 19 Sept. 2012Bone_tissue.ppt24 Fracture repair Fracture hematoma –At time of break blood vessels rupture, clot forms –Macrophages, osteoclasts clean up Internal and external fibrocartilaginous callus –Fibroblasts & osteoblasts enter site and lay down collagen fibers & cartilage matrix.

25. 19 Sept. 2012Bone_tissue.ppt25 Fracture repair Bony callus –Osteoblasts lay down spongy bone trabeculae –Join broken ends Remodeling –Osteoblasts continue forming bone –Compact bone replaces spongy bone