1. 8 th lecture December 10, 2015 Specialized Connective Tissue [Bone (Osseous) Tissue]

2. Bone: Bone is a specialized connective tissue composed of calcified intercellular material, the bone matrix and cells. The main function of bone tissue are: bone tissue provides solid support for the body, protects vital organs such as those in the cranial and thoracic cavities, and harbors cavities containing bone marrow where blood cells are formed. Bone (or osseous) tissue also serves as a reservoir of calcium, phosphate, and other ions that can be released or stored in a controlled fashion to maintain constant concentrations in body fluids. In addition, bones form a system of levers that multiply the forces generated during skeletal muscle contraction and transform them into bodily movements. This mineralized tissue therefore confirms mechanical and metabolic functions to the skeleton.

3. Classification of Bone by Shape Long Short Flat Irregular

4. Bone Matrix Solid ground is made of mineral crystals 2/3 of bone matrix is calcium phosphate, Ca 3 (PO 4 ) 2 : – reacts with calcium hydroxide, Ca(OH) 2 to form crystals of hydroxyapatite, Ca 10 (PO 4 ) 6 (OH) 2 which integrates other calcium salts and ions

5. Bone Matrix Matrix Proteins- 1/3 of bone matrix is protein fibers (collagen type I) Mineral salts make bone rigid and compression resistant but would be prone to break down Collagen fibers add extra tensile strength but mostly add torsional flexibility to resist break down

6. There are four major types of cells in matrix only endosteum only periosteum + endo

7. 1. Osteoblasts Immature bone cells that secrete matrix compounds (osteogenesis) Eventually become surrounded by calcified bone and then they become osteocytes Figure 6–3 (2 of 4)

8. 2.Osteocytes Mature bone cells that maintain the bone matrix Figure 6–3 (1 of 4)

9. Osteocytes Live in lacunae Found between layers (lamellae) of matrix Connected by cytoplasmic extensions through canaliculi in lamellae (gap junctions) Do not divide Maintain protein and mineral content of matrix Help repair damaged bone

10. 3. Osteoprogenitor Cells Mesenchyme stem cells that divide to produce osteoblasts Are located in inner, cellular layer of periosteum Assist in fracture repair

11. 4. Osteoclasts Secrete acids and protein-digesting enzymes Figure 6–3 (4 of 4)

12. Osteoclasts Giant, mutlinucleate cells Dissolve bone matrix and release stored minerals (osteolysis) Often found lining in endosteum lining the marrow cavity Are derived from stem cells that produce macrophages

13. Homeostasis Bone building (by osteocytes and -blasts) and bone recycling (by osteoclasts) must balance: – more breakdown than building, bones become weak – exercise causes osteocytes to build bone

14. Bone membranes Periosteum: – covers outer surfaces of bones – consist of outer fibrous and inner cellular layers – Contains osteblasts responsible for bone growth in thickness

15. Functions of Periosteum 1.Isolate bone from surrounding tissues 2.Provide a route for circulatory and nervous supply 3.Participate in bone growth and repair

16. Endosteum An incomplete cellular layer: lines the marrow cavity covers trabeculae of spongy bone lines central canals Contains osteoblasts, osteoprogenitor cells, and osteoclasts Is active in bone growth and repair

17. Gross Anatomy of Bones: Bone Textures Compact bone – dense outer layer Spongy bone – honeycomb of trabeculae filled with yellow bone marrow

18. 6-18 Flat Bones of the Skull (compact bone) Two layers of compact bone – Inner table – Outer table Region of spongy bone sandwiched between them – Called the diploe Both layers of compact bone are covered by periosteum

19. 6-19

20. Osteon The basic structural unit of mature compact bone Osteon = Osteocytes arranged in concentric lamellae around a central canal containing blood vessels – Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen

21. Compact Bone Figure 6–5

22. Three Lamellae Types Concentric Lamellae Circumferential Lamellae – Lamellae wrapped around the long bone line tree rings – Binds inner osteons together Interstitial Lamellae – Found between the osteons made up of concentric lamella – They are remnants of old osteons that have been partially digested and remodeled by osteoclast/osteoblast activity

23. Compact Bone Figure 6–5

24. Microscopic Structure of Bone: Compact Bone Figure 6.6a

25. Microscopic Structure of Bone: Compact Bone Figure 6.6b

26. Microscopic Structure of Bone: Compact Bone Figure 6.6c

27. Spongy Bone Tissue Makes up most of the bone tissue in short, flat, and irregularly shaped bones, and the head (epiphysis) of long bones; also found in the narrow rim around the marrow cavity of the diaphysis of long bone

28. 6-28 Spongy Bone Microanatomy No osteons In trabeculae: – Parallel lamellae – Osteocytes in lacunae – canaliculi

29. 6-29

30. 6-30