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Composition of bones by mass

Composition of bones by mass. 15-20% water (helps - mechanical properties, nutrients, etc.) 70 % minerals ( Ca 2+ salts in crystal form - hydroxyapatite) 5-10% organic (cells, proteins – ex. collagen ). Collagen. Type I - structural protein > right handed triple helix.

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Composition of bones by mass

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  1. Composition of bones by mass • 15-20% water • (helps - mechanical properties, nutrients, etc.) • 70 % minerals • (Ca2+ salts in crystal form - hydroxyapatite) • 5-10% organic • (cells, proteins – ex. collagen)

  2. Collagen • Type I - structural protein • > right handed triple helix Cross-links (x-links)- provide stiffness

  3. Collagen Provides strength • Type I - structural protein • > right handed triple helix Vitamin C Small size allows turning in helix Forms cross-links • stiffness Lysyl oxidase

  4. Organic (non-mineral) Bone Content • 3. Protein Related • Glycoproteins(95% PRO, 5% CHO) • & • Proteoglycans (glycosaminoglycans) • • (5% PRO, 95% CHO) • * form “ground substance” or glue with water • * communicating mechanical stress, chemicals, • hormones to genes in nucleus

  5. ORGANIC BONE CONTENT • 4. Bone Marrow • * contained in medullary cavity, ends of bones • Yellow- adipose > Red - makes RBC, WBCs, platelets, osteoclasts, osteoblasts

  6. BONE MARROW Red - makes RBC, WBCs, platelets, osteoclasts, osteoblasts

  7. NON-MINERAL BONE CONTENT • 5. Periosteum – Two layer membrane surrounding the bone. >Ligaments and tendons insert/interface w/ periosteum. >Contains nerves and blood vessels. >a source of osteoblasts.

  8. BONE CONSTRUCTION • Epiphysis – End of a bone. Separated from shaft epiphyseal plate (cartilage replaced by bone by adulthood) • Diaphysis – The shaft of a bone. • Articular Cartilage – slick hyaline cartilage on ends of bones - articulate w/ other bones.

  9. Bone Construction articular cartilage cancellous bone cortical bone periosteum

  10. CLASSES OF BONE TISSUE • Cancellous (spongy) or trabecular • 30-90% non-mineralized • has a swiss-cheese geometry (& contains marrow) • found at ends of long bones, vertebrae • Higher surface area --> blood flow and metabolism than cortical bone • Adapts faster to mechanical stress & strain • Cortical • 5-30% non-mineralized • Found in the shafts of long bones • Stronger, stiffer, & denser than cancellous bone

  11. CLASSES OF BONE TISSUE • CorticalCancellous or trabecular

  12. Human proximal femur, frontal section (b is radio-graph of bone section in a) Both figures from Weiss L. Cell and Tissue Biology, A Textbook of Histology, 1988

  13. Anisotropic Nature of Bones • Anisotropic: a tissue - different material properties against different types of loads • • ex. Tendons have much higher strength against tension than compression Bone strengths -tibia

  14. Anisotropic Nature of Bones compression shear

  15. Anisotropic Nature of Bones Compression - weight bearing, pushing objects Tension - muscle contractions Walking - compression, some tension, a little shear Running - compression and tension

  16. Regulation of BONE GROWTH, LOSS(deposition, resorption) • 1. Biomechanical stress, strain • 2. Osteoclast, osteoblast population, activity • • strongly influenced by stress & strain • Ca++ in diet - Ca2+homeostasis critical to heart, neuron, myocyte etc. cell health) • • maintain blood [Ca++] = 5 mEq (10 mg/dl) • • diet - only ~ 1/3 absorbed • • absorption affected by stomach pH, hormones (parathyroid hormone), Vitamin D, fiber in diet, etc. • • most Americans (especially females) do not get enough calcium in the diet to optimize growth and maintain bone mass!!

  17. Calcium intake • Age Min Daily Req. NIH Recommends • 0-10 1000 mg 800-1200 mg • 11-24 1200 mg 1200-1500 mg • 25-50 1000 mg 1000 mg • 50-65 (W) 1000 mg 1000 mg (w/estrogen) • 50-65 (W) 1000 mg 1500 mg (no estrogen) • 65 + 1000 mg 1500 mg • pregnant W 1200 mg 1200-1500 mg • 90% of Americans are not getting enough calcium in the diet • Is 1500 mg/day a goal for all?

  18. Sources of Calcium: • Milk (8 oz): 300 mg • Yogurt (8 oz): 350 mg • Calcium-fortified orange juice: 300 mg • Sardines (8 med): 350 mg • Spinach (1 cup): 245 mg • Collard greens: 350 mg

  19. Calcium Supplements: • Calcium carbonate • Calcium citrate • Calcium lactate • Calcium gluconate • Coral calcium • Should dissolve in vinegar in 20 min

  20. Regulation of BONE GROWTH, LOSS • 4. Vitamin D • • produced and activated by UV light OR • • absorbed by diet and • activated by parathyroid hormone in the kidney • to 25-Hydroxyvitamin D • • active 25-Hydroxyvitamin D • needed to increase Ca2+ absorption by intestine

  21. Regulation of BONE GROWTH, LOSS • 5. Hormones A. estrogen, testosterone • sex hormones - androgens • receptors for estrogen on osteoblasts & osteoclasts • estrogen limits excess resorption - osteoclasts • estrogen increases protein synthesis, Ca2+ deposition - osteoblasts > osteoblasts (growth factors - IGF-1, TGF) 90% decrease in estrogen after menopause • testosterone involved in protein synthesis *slowly decreases with age

  22. Regulation of BONE GROWTH, LOSS • 5. Hormones • B. calcitonin, parathyroid hormone control Ca2+ levels in blood • calcitonin - thyroid gland • * when Ca2+ in blood high --> increased release of calcitonin > increases deposition of Ca2+ on bones • > potent anti-resorptive effects (osteoclasts) • > increased production of osteoblasts, IGF-1 release • > used in therapy against osteoporosis

  23. Regulation of BONE GROWTH, LOSS • 5. Hormones • B. calcitonin, parathyroid hormone control Ca2+ levels in blood • parathyroid hormone (PTH) - parathyroid gland • * Ca2+ levels --> PTH release • PTH activates Vitamin D --> 1,25 Vit D • *increases intestinal absorption of Ca2+ • > PTH increases renal reabsorption of Ca2+ • moves Ca2+ from bone into the blood • PTH can stimulate both osteoclasts (chronic) • and osteoblasts(via IGF-1) (intermittant) • PTH low in some women with osteoporosis

  24. Regulation of BONE GROWTH, LOSS • 5. Hormones • C. Growth Hormone (GH) • produced by pituitary gland • protein synthesis through somatomedins > growth factors * IGF-1 (insulin-like growth factor) * TGF (transforming growth factor) • • GH levels may increase (≥500%) with exercise!! * intensity and duration dependent

  25. Regulation of BONE GROWTH, LOSS • 5. Hormones • D.thyroxine • produced by thyroid gland • protein synthesis, metabolism • increases with exercise • hypothyroid conditions increase with age

  26. Regulation of BONE GROWTH, LOSS • 6. Pharmaceuticals • • antacids (especially aluminum or magnesium salts) increase pH in stomach; interfere with absorption • • corticosteroids (cortisone, prednisone) anti-inflammatory and catabolic steroid; decrease protein synthesis, increase protein loss • • alcohol (high intake) • • caffeine - three cups of coffee/day

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