Bone Physiology

1. Bone Physiology

2. Bones are Classified by shape and structure limbs Carpals tarsals vertebrae Skull bones Ribs Sternum scapula

4. EpiphysisEpiphyseal LineDiaphysisPeriosteumArticulating Cartilage Anatomy of Long Bone

5. Compact Bone • Canaliculi • Haversian Canal • Lamellae • Osteon

6. Another picture of Compact Bone

7. Compact Bone

8. Spongy Bone Located along the epiphyses of long bonesSite of Erythrocyte (RBC) formation Collagen fibers are not arranged in concentric rings. But the lamellae form rods called trabeculae. No Osteons or Haverian Systems are present.

9. Cells in Bones Osteocyte – mature bone cells; recycle Ca and PO4 Osteoclasts– dissolve bone by secreting enzymes and acids. Release Ca to be returned to blood stream Osteoblasts– cells that produce new bone cells referred to as osteogenesis Osteoclasts remove matrix, osteoblasts adds matris. When an osteoblast’s lacunae is calcified the cell becomes and osteocyte.

10. Endochondrial Ossification • Bone tissue in a fetus begins as hyaline cartilage • Inside is cartilage, cartilage becomes ossified. • In 6 weeks cartilage is replaced tobone except at growth plates.

11. In 6 weeks cartilage is replaced to bone except at growth plates.

13. Longitudinal Growth at the Epiphyseal line

14. Two growth plates • Composed of hyaline cartilage • Longitudinal growth is completed when epiphyseal lines become completely ossified.

15. Chrondroblasts closest to epiphyses begin to undergo cell division • Cells enlarge (hypertrophy) • Cells die, bone eventually replaces cartilage (invasion zone)

16. Resting Zone Mitosis Zone Hypertrophy Zone Ossification Zone

17. Growth along Epiphyseal Line Mitosis Zone • Resting Zone

18. Maturation/Hypertrophy Zone • Ossification Zone

19. Longitudinal Growth • Controlled by 3 hormones • Growth Hormone • Baby to prepuberty • Sex Hormones (estrogen/testosterone) • Causes growth spurt at puberty • Shapes your skeleton to your sex • Thyroid Hormones (PTH & Calcitonin) • PTH = parathyroid hormone • Controls whether bone growth occurs • Affects Appositional Growth – bone growth in diameter

20. Bone HomeostasisBone Remodeling • Osteons are formed by osteoblasts • In healthy adults: • Bone deposit = bone resorption • Osteoblasts = Osteoclasts • Bone Remodeling refers to the regular mineral turnover that occurs in bone. • In adults, 18 % of proteins and minerals turns over yearly. Not uniform. I.e. Head of femur is remodeled more. Why?

21. Bone RemodelingControlled by Negative Feedback Loop • Bone Deposit • Occurs where bone is injured or added bone strength is required • Deposits Ca+2 into bone • Bone Resorption • Osteoclasts break down bone • Calcium is taken from bone and placed into blood stream • Lysosomes assist in the process • Ca and PO4 are released; eventually releasing the blood stream

22. Bone Remodeling is controlled by 2 hormones by a Negative Feedback Loop • Blood Calcium is the original stimulus • Normal Blood Ca is 9-11 mg CA/100 ml of blood • When blood Ca decreases (< 9 mg) Parathyroid Hormone (PTH) is released into bloodstream. • Bone resorption occurs causing Ca to leave bone and goto the blood stream • Osteoclasts are working

23. High levels of blood Ca (>11mg) • When blood Ca levels are high, Calcitonin is released. • Causes bone deposit to occur • Ca from the blood is stored into bone. • (Osteoblasts and Osteocytes are working.) • 99% of all Ca is found in bone.

24. PTH Calcitonin

25. Osteoclasts cause bone resorption • Controlled by PTH • Osteoblasts cause bone deposit • Controlled by calcitonin

26. Factors that help with Bone Deposit • Vitamin D – aids in the absorption of Calcium into the bone. Part of vitamin D is converted to the hormone calcitriol which allows Ca to pass through the S.I.(What food is Vitamin D fortified?) i.e. rickets results from Vitamin D deficiency • Vitamin C – helps osteoblasts function i.e scurvy – caused from a reduction in osteoblast activity • Calcium tablets - • Diet -

27. Appositional Growth over time.

28. 2nd Response to Regulating Bone Remodeling • Wolff’s Law • Bone grows or remodels in response to the forces or stresses placed on it. • Appositional growth – growth in diameter is controlled by the amount of mechanical stress and gravity placed on the bone • Heavy usage leads to heavy bones; nonuse leads to atrophy (bone loss)

29. Controlling Bone Remodeling • Hormones PTH and Calcitonin determines whether and when bone remodeling occurs. • Mechanical Stess determines where remodeling occurs. High stress areas grow appositionally.

30. Body’s Needs for Calcium • Transmit nerve impulses • Muscle contractions • Blood coagulation • Cell division If blood Ca levels are low for an extended time, bones continually lose Ca. Once bone density loss begins, women lose 8% of their bone mass every decade, men lose 3% every decade

31. Osteoporesis • Osteoporesis • Normal Bone Risk Factors Sex (females more affected than males; especially after menopasue) Insufficient exercise or too much exercise Poor diet (low in Ca and protein Smoking Race: Black > bone density

32. Change in Bone Density with Age

33. Bone Fracture and Repair • Simple Fractures take 8-12 weeks to heal • Healing time increases age due to poor circulation

34. Phases of Bone Repair Hematoma formation • A mass of clotted blood appears • Blood vessels hemorrhage, causing internal bleeding • Blood pools and clots around fx area; which closes off injured blood vessels

35. Fibrocartilage Callus Formation • Macrophages invade and clean area • Fibroblasts help form chondroblasts and collagen fibers • Helps to form cartilage splint that will connect ends of broken bones

36. Bony Callus • Osteoblasts replace the cartilage with spongy bone • Bone cells replace cartilage from the outside fx toward the inside • Cells are not organized in the bony callus

37. Bone Remodeling Continues 4 months to a yearRemoves excess material; a layer of compact bone is produced