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Chapter 7

Chapter 7. Skeleton & Skeletal Structure. Function. Support – provide surfaces for anchoring soft organs. Protection – skull, ribs, vertebrae Movement – anchor muscles; joints are pivot places, bones are levers. Storage – fat, minerals (Ca, P, K, Na, S, Mg, Cu,); 2/3 of bone weight.

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Chapter 7

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  1. Chapter 7 Skeleton & Skeletal Structure

  2. Function • Support – provide surfaces for anchoring soft organs. • Protection – skull, ribs, vertebrae • Movement – anchor muscles; joints are pivot places, bones are levers

  3. Storage – fat, minerals (Ca, P, K, Na, S, Mg, Cu,); 2/3 of bone weight Hematopoiesis – red marrow makes RBC’s, WBC’s, platelets in adults; liver & spleen in infants

  4. CLASSIFICATION Compact • Type of bone tissue: • Compact – dense & smooth • Spongy (cancellous) – open spaces with “girders” Spongy

  5. Trabeculae – “girders”

  6. Shape • Long bones – (femur, humerus, phalanges, etc.); compact; shaft w/2 ends; act as levers

  7. Short bones – (carpals, tarsals); cube-like • often embedded in joints to articulate tendons

  8. spongy w/compact on surface • bones glide across one another in multiple directions

  9. Flat bones (cranium, ribs, shoulder) • protect soft organs • provide for large muscle attachment • 2 compact bone surfaces w/spongy in between

  10. Structure of a Flat Bone • External and internal surfaces composed of compact bone • Middle layer is spongy bone and bone marrow • Skull fracture may leave inner layer of compact bone unharmed

  11. Irregular(bones of the inner skull, vertebrae, hip) • varied for articulation with muscles, tendons, and ligaments

  12. STRUCTURE (Gross) • Diaphysis – shaft • cylinder of compact bone • Covered with periosteum • Medullary cavity – center of bone • yellow marrow found here (fat) • Lined with endosteum

  13. Epiphysis – ends of long bones spongy with red marrow covered by compact bone and hyaline cartilage Epiphyseal disk (plate) – ends of long bones; covered in hyaline cartilage, points of growth; replaced by bone at time of growth = epiphyseal line Predictable growth rates

  14. Endosteum – membrane lining the inside of shaft; contains: • Osteoblasts – bone forming cells on the outside • Osteoclasts – bone resorption cells on the inside

  15. Periosteum – outer membrane on the diaphysis • Articular Cartilage – ends of articulating long bones; cushions and absorbs stress • Nutrient Formina – holes for blood vessels and nerves

  16. Structure of a Long Bone • Compact and spongy bone • Marrow cavity • Articular cartilage • Periosteum

  17. STRUCTURE (Microscopic) • Haversian system (osteon) – structural unit of bone; consists of: • Hard bone matrix arranged in rings (lamellae) • Central canal (Haversian canal) through which vessels run

  18. Volkmann’s canals – perpendicular to Haversian canals; connects nerves and blood vessels to periosteum • Osteocytes – spider-shaped; lie in lacunae • Canaliculi – canals that link lacunae to each other and to Haversian canals

  19. Blood Vessels of Bone

  20. Spongy – consists of trabeculae (fibers) • Irregularly arranged lamellae and osteocytes • No osteon present

  21. Spongy Bone Structure and Stress

  22. CHEMICAL COMPOSITION • Organic • contributes to bone structure • helps resist stretch and twist forces (tensile strength) • 1/3 of bone matrix is organic • consists of: proteoglycans, glycoproteins, and collagen. Material is secreted by osteoblasts

  23. Inorganic • 2/3 of bone weight • contributes to bone hardness (compression strength) • Mineral salts (Ca3PO4, CaOH2, CaCO3) • Can resist 25,000 lb/in2 of compression and 15,000 lb/in2 of tension • Lasts well past death Low calcium = porous bones

  24. Bone Growth • Pts of skeleton begin to form within first few weeks of prenatal development

  25. BONE GROWTH • Longitudinal Growth (length) • Chondroblasts slow their growth at the distal end of the epiphysis • The chondroblasts are replaced by osteocytes • Growth stops when the epiphyseal plates fuse with the bone; occurs in late adolescence

  26. Appositional growth (diameter) Thickness can continue with stress from excessive muscle activity and/or body weight; accomplished through the antagonistic actions of osteoclasts and osteoblasts

  27. Animation:Bone Growth in Width Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

  28. Hormonal Regulation • Human Growth Hormone – stimulates mitosis at epiphyseal plates

  29. Sex hormones – causes growth spurts; molds male and female skeletons • Girls grow faster than boys and reach full height earlier (estrogen stronger effect) • Boys grow longer and taller • Use of anabolic steroids causes growth plate to close prematurely

  30. Hypo- or hypersecretions – can cause “gigantism” or “dwarfism”

  31. Dwarfism • Achondroplasia • long bones stop growing in childhood • normal torso, short limbs • spontaneous mutation during DNA replication • failure of cartilage growth • Pituitary • lack of growth hormone • normal proportions with short stature

  32. REMODELING • Occurs at the tissue level, not at the cellular level as in other systems • Deposition and Resorption results in remodeling • Unequal by area – for example the femur is replaced every 5-6 months

  33. Deposition • occurs at an area of stress or breakage • Osteoblasts put bone material down on the outside surface of the bone • Dental braces reposition teeth and remodel bone through pressure variances

  34. Abnormal calcification (ectopic) may occur in lungs, brain, eyes, muscles, tendons or arteries (arteriosclerosis)

  35. Resorption – Osteoclasts absorb bone material from the inside of the bone • Control • Hormonal through a negative feedback mechanism

  36. PTH (parathyroid hormone) is released when calcium levels in the blood are low • This causes osteoclast activity to increase • When Ca+ levels rise, osteoclast activity ceases

  37. Calcitonin is released when Ca+ levels are high; this inhibits bone resorption and stimulates osteoblasts to put bone material down on the outside of the bone.

  38. When Ca+ levels fall, calcitonin release is stopped • This mechanism balances Ca+ levels in the blood. • Calcium needed in neurons, muscle contraction, blood clotting and exocytosis • ~1100g in adult skeleton • plasma concentration is ~ 10 mg/dL

  39. Hormonal Control of Calcium Balance • PTH and calcitonin maintain normal blood calcium concentration.

  40. Ca+ is absorbed from food in the intestines in the presence of activated Vitamin D. • Abnormal softness (rickets) in children and (osteomalacia) in adults without vitamin D

  41. Mechanical/gravity/stress causes remodeling • Wolff’s law • bone grows or remodels in response to forces or stress • stress causes minute electrical currents to be produced in the bone • currents accelerate osteoblast activity • thus the use of exercise for those with osteoporosis.

  42. Hormones determine whether or when remodeling occurs • Mechanical stress determines where remodeling occurs.

  43. REPAIR • Required when trauma, pathology has occurred • Fracture – treated by “reduction” • Closed reduction – manipulation of ends of bones outside the skin to align ends • Open reduction – requires surgery and wires/pins • Traction – risks long-term confinement

  44. Types of Bone Fractures

  45. Fractures

  46. Phases of Repair 1. Hematoma formation – blood clot; cells die (hours) 2. Callus formation – forms soft tissue then a callus; capillaries grow, phagocytes eat up callus (days)

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