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Bone Tissue

Bone Tissue. Dynamic tissue, continually remodels Bone tissue (osseous tissue) a connective tissue with a matrix hardened by minerals bones make up the skeletal system Functions of the skeletal system

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Bone Tissue

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  1. Bone Tissue • Dynamic tissue, continually remodels • Bone tissue (osseous tissue) • a connective tissue with a matrix hardened by minerals • bones make up the skeletal system • Functions of the skeletal system • support, protection, movement, blood formation, mineral reservoir, and pH balance

  2. Structure of a Flat Bone • Surfaces of flat bone are composed of compact bone • Middle layer is spongy bone. No marrow cavity

  3. Structure of a Long Bone

  4. Cells of Osseous Tissue • Osteoprogenitor (osteogenic) cells reside in endosteum and periosteum • Osteoblasts form organic matter (__________) of matrix & help to mineralize it with calcium phosphate • Osteocytes are osteoblasts that have become trapped • reside in _______ and connected to each other by __________ • signal osteoclasts & osteoblasts about mechanical stress

  5. Cells of Osseous Tissue • Osteoclasts develop in bone marrow by the fusion of the same stem cells that give rise to __________________ • Osteolysis within resorption bays

  6. Matrix of Osseous Tissue • Dry weight is 1/3 organic & 2/3 inorganic matter • Organic matter • collagen, glycosaminoglycans, proteoglycans & glycoproteins • Inorganic matter • 85% _______________________________________ • 10% calcium carbonate • other minerals • Combination provides for strength & resilience • minerals resist compression; collagen resists tension

  7. Compact Bone • Osteons or haversian systems • cylinders of tissue formed from layers of matrix concentrically arranged around a blood vessel • ______________ are the individual layers • osteocytes connected to each other and the haversian blood supply by tiny cell processes • Perforating canals or Volkmann canals • branches from nutrient arteries that run perpendicular to the haversian canals • Circumferential or outer lamellae

  8. Histology of Compact Bone

  9. Spongy (Cancellous) Bone • Spongelike appearance - trabeculae • spaces filled with red bone marrow • Trabeculae have few haversian systems • Provides strength with little weight • trabeculae develop along bone’s lines of stress

  10. Bone Marrow • Soft tissue within the medullary cavity of a long bone or the spaces amid the trabeculae of spongy bone • Red marrow looks like thick blood • mesh of reticular fibers and immature cells • _________________________ • in adults found in axial skeleton & girdles • Yellow marrow • marrow of long bones in adults consisting mostly of _________________________

  11. Intramembranous Ossification • Produces flat bones of skull and mandible • Steps of the process • mesenchyme condenses • osteoprogenitor cells • osteoblast form osteid • minerals deposited • osteocytes • osteoclasts remodel center & osteoblasts remodel surface • mesenchyme - periosteum

  12. Endochondral Ossification • Primary ossification center forms in cartilage model • chondrocytes near the center swell (______________) • bony collar formations • forms primary ossification center • Marrow space formed by periosteal bud • osteogenic cells invade & transform into osteoblasts • osteoid tissue deposited and calcified into trabeculae; at same time osteoclasts work to enlarge the primary marrow cavity

  13. Endochondrial Ossification

  14. Metaphysis • Transitional zone between diaphysis and epiphysis • Five zones of activity • reserve cartilage • cell proliferation • cell hypertrophy • calcification • bone deposition

  15. Bone Growth and Remodeling • Grow and remodel themselves throughout life • growing brain or starting to walk • athletes or manual laborers have ↑ bone density & mass • Cartilage grows by appositional & interstitial growth • Can bone increase in length by interstitial growth? • Bones increase in width by _________________________growth • if one process outpaces the other, bone deformities occur

  16. Mineral Deposition • Mineralization - certain ions are removed from blood plasma & deposited in bone tissue • Steps of mineralization • osteoblasts produce ____________ fibers that spiral along the length of the osteon in alternating directions • fibers become encrusted with minerals hardening matrix • ion concentration must reach the solubility product for crystal formation to occur & then positive feedback forms more • Ectopic ossification is abnormal calcification • may occur in _________________________________

  17. Mineral Resorption • Process of dissolving bone & releasing minerals into the blood • performed by __________________ • hydrogen pumps in cell membrane secrete hydrogen ions • chloride ions follow by electrical attraction • hydrochloric acid & a low pH dissolve bone minerals • enzymes (acid phosphatase, cathepin K) digest the collagen • Braces reposition teeth • stimulating osteoclasts & osteoblasts to remodel jaw

  18. Osteoclast Activity Cl-

  19. Functions of Calcium & Phosphate • Phosphate is a component of DNA, RNA, ATP, phospholipids, & acid-base buffers • Calcium is needed for communication between neurons, muscle contraction, blood clotting & exocytosis

  20. Ion Imbalances • Changes in phosphate conc. have little effect • Changes in calcium can be serious • hypocalcemia is deficiency of blood calcium • causes excessive excitability of nervous system leading tomuscle spasms, tremors or tetanus • calcium normally contributes to resting membrane potential • hypercalcemia • excessive calcium at cell surface makes sodium channels less likely to open, depressing nervous system • Homeostasis depends on calcitriol, calcitonin & PTH

  21. Bone Hormones

  22. Calcitriol Synthesis & Action Lack of this leads to Rickets or Osteomalacia

  23. Calcitonin • Secreted by C cells of the ______________ gland when calcium concentration rises too high • Functions • reduces osteoclast activity quickly • increases calcium loss by kidneys • Important role in children, but little effect in adults • calcitonin deficiency does not cause any adult diseases

  24. Parathyroid Hormone • Secreted by the parathyroid glands • Released when calcium blood level is too ______ • Functions • inhibits activity of ____________________ • stimulates osteoclast multiplication & activity • reduces calcium secretion & increases phosphate secretion in the urine • stimulates the production of an enzyme in the kidneys that carries out the last step in calcitriol synthesis

  25. Control of Calcium Levels

  26. Types of Bone Fractures

  27. Healing of Fractures • Normally healing takes 8 - 12 weeks • Stages of healing • fracture hematoma (1) • broken vessels form a blood clot • granulation tissue (2) • fibrous tissue formed by fibroblasts & infiltrated by capillaries • callus formation (3) • soft callus of fibrocartilage replaced by hard callus of bone in 6 weeks • remodeling (4) • occurs over next 6 months as spongy bone is replaced with compact bone

  28. Healing of Fractures 1 2 3 4

  29. Osteoporosis • Most common bone disease • Bones lose mass & become brittle • loss of organic matrix & minerals • ____________________ - most risk • by age 70, average BM loss is 30% • Best treatment is prevention -- exercise & calcium intake (1000 mg/day) between ages 25 and 40 • Drugs • HTR • Fosamax • Statins

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