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Skeletal System

Skeletal System. Structure & Function Development & Growth Bone Homeostasis Osteoporosis & other bone disorders. The evil that men do lives after them, the good is oft interred with their bones. —William Shakespeare (1564-1616) Julius Caesar, Act III, Scene 2.

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Skeletal System

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  1. Skeletal System Structure & Function Development & Growth Bone Homeostasis Osteoporosis & other bone disorders The evil that men do lives after them, the good is oft interred with their bones. —William Shakespeare (1564-1616) Julius Caesar, Act III, Scene 2

  2. A Bone’s Shape Makes Possible its Functions • Shape & form • Support • Protection • Movement • Storage • Hematopoiesis Sites of muscle attachments

  3. Bone Structure • Structures of a long bone: • periosteum: tough fibrous membrane covering • diaphysis: shaft - b/t epiphyses, long axis of bone • articular cartilage: portion of epiphysis covered w/ cartilage • epiphysis: expanded ends of bone -- proximal & distal • medullary cavity: hollow chamber w/in diaphysis, endosteum membrane lines cavity & marrow resides w/in • compact bone (cortical): near surface, continuous ECM w/ no spaces -- dense & hard • spongy bone (cancellous): w/in compact bone, consists of network of thin strands of trabeculae

  4. Gross Anatomy of a Long Bone

  5. Cellular Structure of Bone Compact bone: cells, ECM & mineral salts form an osteon contain blood vessels & nerves surrounded by CT perforating canals transverse central canals osteocytes lie in small concavities (lacunae) b/t lamellae canaliculi - provide communication b/t osteocytes Spongy bone: cells & ECM lie w/in trabeculae no osteon or central canals – irregular lamellae & osteocytes trabeculae are formed where stress is exerted on the bone receive nutrients via diffusion from the canaliculi

  6. Structural Unit of Compact Bone: Osteon

  7. Lamella

  8. Microscopic Structure of Spongy Bone

  9. Gross Anatomy of a Long Bone

  10. Principal Cells of Bone Tissue

  11. Chemical Composition of Bone • Organic components: • Cells: osteogenic, osteoblasts, osteocytes & osteoclasts • ECM: contribute to bone’s structure & tensile strength • Inorganic components: • mineral salts: calcium phosphate & carbonate which account for bone’s hardness

  12. Osteogenesis • Intramembranous ossification (flat & irregular): - originate as sheet-like layers of CT - partially differentiated CT form into osteoblasts - deposit bony matrix -- forming spongy bone • Endochondral ossification (long & short): - develop from hyaline cartilage -- model for bone formation - CT covering cartilage becomes infiltrated w/ blood vessels forming periosteum - CT differentiates into osteoblasts forming spongy bone w/ ossification continuing deposition of compact bone occurs

  13. Intramembranous Ossification

  14. Stages in Endochondral Ossification Occurring in a Long Bone

  15. Endochondral Ossification Forming skeleton of an embryonic chicken, stained with Alizarin Red and Alcian Blue to differentiate between hardened bone (in red) and the remaining cartilage model (in blue).

  16. Bone Growth : elongation & appositional Epiphyseal Plate http://highered.mcgraw-hill.com/classware/infoCenter.do?isbn=0072829532

  17. X-ray Depicting Epiphyseal Plate

  18. Osteoclasts & Medullary Cavity • Multinucleated cells originate from WBC -- break down calcified matrix (bone resorption): • lysosomal enzymes digest organic components • acids secreted dissolve inorganic portion of matrix • phagocytes digest bony matrix • osteoblasts invade depositing new bone • Formation of medullary cavity: • primary ossification center enlarges -- osteoclasts break down spongy bone • cavity forms in center of diaphysis • cavity fills w/ marrow, blood & lymph vessels & nerve fibers • red & yellow marrow

  19. Bone–Resorbing Osteoclast

  20. Development of osteoblasts &osteoclasts from bone marrow progenitors Valsamis et al.Nutrition & Metabolism 2006 3:36

  21. Homeostasis: Bone Remodeling • Continuous bone resorption & bone deposition –regulated via 2 control loops: 1. negative feedback (hormonal) 2. mechanical/gravitational (Wolff’s law of bone)

  22. Hormonal Control of Blood Ca++ • When Ca++ intake is ¯ -- blood [Ca++] are also ¯ • PTH stimulates osteoclasts -- releasing Ca++ salts from ECM into blood • High intake ­ blood [Ca++] inhibits osteoclasts activity • Calcitonin -- stimulates osteoblasts activity, ¯ bone resorption & ­ Ca++ excretion (hypercalcemia) (hypocalcemia)

  23. Hormonal Control of Ca++ Balance • Parathyroid hormone (PTH) – responsible for ­ plasma [Ca++] • mobilize Ca++ from bone (­ bone resorption) • enhances renal reabsorption of Ca++ • ­ intestinal absorption of Ca++ (indirectly) • Vitamin D3– 1,25-dihydroxycholecalciferol (calcitriol): • obtained from diet & sunlight • supports effect of PTH – enhancing Ca++ uptake in small intestine • PTH & prolactin regulate production • Calcitonin: • released in association w/ ­ plasma [Ca++] • ¯bone resorption & ­ renal excretion (action opposite to PTH)

  24. Factors Affecting Bone Development, Growth & Repair • Nutrition: calcium, phosphorus, vitamins D, A, C & K • UV radiation: dehydrocholesterol • Hormones: hGH, T3 & T4, PTH and male & female sex hormones • Physical activity: weight bearing exercise & skeletal muscle contraction (Wolff’s Law)

  25. Fractures & Repair • Fracture: classified by cause & nature of break (e.g., traumatic, compound) • Blood vessels & periosteum rupture -- hematoma, swelling & inflammation to surrounding tissue • Angiogenesis: osteoblasts invade hematoma generating spongy bone nearby & fibroblast produce fibrocartilage (cartilaginous callus) and ECM • Phagocytic cells remove blood clot & osteoclasts resorb bone fragments

  26. Key Steps in Repair of a Fracture

  27. Types of Fractures

  28. Rickets & Osteomalacia • Pathology: failure of osteoid to calcify in a growing person, most commonly assoc. w/ vitamin D deficiency in hypocalcemia • Signs & Symptoms: muscular hypotonia, thickening of skull, softening of long bones (bowlegs), knobby deformity in long bones & ribs, kyphoscoliosis • Risk factors: dark skin, inner-city dwellers, breastfeed infants w/o vitamin D supplementation • Treatment: UV light, vitamin D, calcium & phosphorus supplements,

  29. Osteoporosis • Pathology: ¯ bone mass & mineral content - w/in affected bones trabeculae are lost -- spaces/canals enlarge filling w/ fibrous & fatty tissues • Signs & symptoms: bones fracture easily (long bones), spontaneous breaks - unable to support body weight • Risk factors: ¯ Ca++ & vitamin D intake, ¯ phys. act., ¯ estrogen levels, cigarette smoking, alcohol abuse, • medications: gender, age, body • size, ethnicity & genetics • Screening & Treatment: DEXA; bisphosphonates; estrogen • therapy (ERT); PTH & exercise

  30. Bone Mineral Acquisition During Puberty • Bone mineral density (BMD) ­ most rapidly b/t ages of 11-14 yrs in girls & 14-17 yrs in boys • Females reach 95% of adult BMD by age 18 yrs & w/ only modest gains up to 3rd decade of life Gap in Ca++ Intake • 86% of girls & 65% of boys aged 12-18 yrs fail to meet RDA of 1200 mg/d for Ca++ • Intake for Ca++ -- 1300 mg/d; gap b/t the recommended & actual intakes has widened

  31. Barriers to Calcium Intake & Other Factors Affecting Bone Mineral Density • Ca++ content of common foods: http://www.nof.org/ • Meeting RDA of Ca++ is challenging when dairy products are not consumed. Ca++ -fortified products offer a means of boosting Ca++ consumption through nondairy foods • Nondairy sources of Ca++ such as breads, cereals, vegetables, and fish, have a lower content or less bioavailable form. Ca++ -rich foods such as DGLV, tofu, nuts, legumes & sardines are not part of the standard diet • Inadequate vitamin D intake, lack of exposure to sunlight & reduced vitamin D receptors in older adults all contribute • Lack of phys. act., smoking, excessive alcohol consumption, diets ­ Na & phosphorus

  32. Spinal Deviations of the Vertebral Column

  33. Intervertebral Disc & Herniation

  34. Carpal Tunnel Syndrome • Pathology: swelling of tendons reduces tunnel space -- squeezing & injuring median nerve • Symptoms: numbness, tingling, pain, inflammation & clumsiness of the hand • Diagnosis & treatment: Tinel’s test, Phalen’s test, nerve conduction • velocity studies, patient history & occupational evaluation; anti- • inflammatory drugs, splints, avoidance of activities causing condition, • surgery and alternative therapies

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