Skeletal system and tissues

1. Skeletal system and tissues

2. Long Bone Anatomy Long Bone as a model bone

3. Diaphysis: • Mostly compact bone • medullary cavity = hollow space • saves weight without compromising strength • Cavity contains yellow marrow • Yellow Marrow = mostly adipose tissue

4. Epiphyses: • Mostly spongy bone with “shell” of compact bone • save weight without compromising needed strength • May contain yellow or red marrow, • Red Marrow = blood cell formation • Epiphyseal Plates: site of longitudinal growth bone growth • Articular cartilage: • Hyaline cartilage at joint surface

5. w/ trabeculae

8. Trabeculae of compact bone are oriented along the paths of structural stress placed on the bone so that bone material is only present where it is most needed. • These trabeculae can be remodelled if stresses change

9. Locations of red marrow in adultred marrow = site of blood cell production Hematocytoblasts (hematopoietic stem cells) Myeloid Stem Cells Lymphoid Stem Cells • Redblood cells • From erythroblasts • Platelets • From megakaryoblast • Granulocytes (WBC) • from myeloblasts • Monocytes (WBC) • From monoblasts • Lymphocytes (WBC) • From lymphoblasts

10. Periosteum:

11. Figure 6.5

12. Periosteum: Structure: Membrane surrounding outer surface of bone Except articular cartilage Outer layer of dense irregular CT Rich in collagen Inner cellular layer Includes osteoblasts, osteoclasts, & osteoprogenitor (i.e., stem) cells Function: Connects tendons and ligaments to bone Sharpeys/perforating fibers Site of bone formation/remodelling Contains blood vessels and nerves that serve the bone. Site of appositional growth

13. Endosteum • lines the inner surfaces of bone • Contains osteoprogenitor (i.e., stem) cells, osteoblasts and osteoclasts • Site of bone formation/remodelling

14. Structure of non-long bones • Periosteum • Endosteum • Spongy bone with trabeculae • and spaces all as in long • bones • No medullary cavity

15. BONE TISSUE • CELLS • Osteoblasts: create matrix • Osteocyctes: maintain matrix, feedback on stress experienced • Osteoclasts: destroy matrix • MATRIX • Calcium salts (calcium phosphate/hydroxyapitite) • Collagen fibers

16. Compact Bone Mid-power High power (close up)

17. Osteon: • repeating structural units of compact bone • oriented the length of long bones (our primary model) osteon

18. Figure 6.8

19. Lamellae= Layers of matrix (collagen + calcium phosphate/hydroxyapitite) • too dense for oxygen, nutrients or wastes to diffuse through(from a practical stand point)

20. Non-osteonic lamellae • Circumferential—around the outside of the entire bone • Interstitial—remnant lamellae found between existing, complete osteons

21. Central Canal: • passageway for blood vessels and nerves

22. Lacunae: • Spaces/cavities containing osteocytes

23. Canaliculi: • Passageways through matrix • interconnect lacunae and central canal • Filled with extensions of osteocytes that are joined by gap junctions • Transport of oxgyen, nutrients, and wastes

24. Perforating canals: • Passageways that interconnect central canals • filled with blood vessels and nerves

25. Spongy (Cancellous) Bone • No osteons • Trabeculae consisting of • Parallel lamallae • Cells obtain nutrients from vessels in contact with surface of trabeculae

26. BONE REMODELLING • The process of constant creation and destruction of bone by osteoblasts and osteoclasts • Bone Remodelling Continually: • reshapes bones in response to the specific stresses placed on them • Gravity • Muscular contraction • Adjust balance of bone creation/destruction to regulate Ca+ and PO4 levels • Also part of bone development (e.g., creation of processes) and repair • Bone is remodelled on its periosteal and endosteal surfaces • On average 20% of our skeleton is remodelled each year (but rates vary widely in different parts of skeleton)

27. BALANCE BETWEEN OSTEOBLAST AND OSTEOCLAST ACTIVITY • Osteoblast activity > osteoclast activity • Net increase in bone mass/amount of bone • Net uptake of calcium and phosphate from blood • Blood Ca and PO4 decreases • Osteoblast activity < osteoclast activity • Net reduction in bone mass/amount of bone • Net release of calcium and phosphate from bone into blood • Blood Ca+ and PO4 increases

29. HORMONES ASSOCIATED WITH THE SKELETAL SYSTEM Calcitonin (from Thyroid) • Inhibits osteoclastacitivity • Encourages bone deposition/creation • Reduces blood Ca+ Parathyroid hormone (from parathyroid gland) • Stimulates osteoclast activity • Encourages bone destruction/Ca+ release • Increases blood Ca+

30. Table 6.1

31. Anatomical Basis of Bone Disorders • Achondroplastic Dwarfism: • Short limbs due to failure of chondrocytes in epipheseal growth zone to divide and enlarge • Results in early closing of plates and thus short limbs • Rickets (a.k.a. osteomalacia) • Lack of vitamin D (and concomitant lack of calcium absorbtion by digestive tract) leads to • Poorly calcified matrix so bones are “soft and flexible”, does make easier to break • Collagen component largely unaffected • Osteoporosis • Loss of bone mass and reduction of microstructure particularly in spongy bone • Makes bones prone to breakage (esp, wrist, hip, and spine), compression (esp. in vert bodies causing height reduction and abnormal curvatures) • Femur fractures in the ederly: • did the fall break the bone or did the bone break cause the fall?

33. Page 167_01

34. synovial joints

35. Fig. 7.34 Synovial Joints • Freely movable • diarthrotic • Articulating bones are separated by space • the joint cavity • Parts Include: • Articular/joint capsule • Joint cavity • Synovial fluid • Articular cartilage • Ligaments • Blood vessels • nerves

36. Fig. 7.34 Joint Capsule: An extension of the periosteum that connects the articulating bones while allowing movement Outer Fibrous Layer • Dense irregular (collagenous) CT • Provides strength • Includes localized thickenings—intrinsic ligaments Inner Synovial membrane • Areolar CT • Covers internal surfaces except articular cartilage • Secretes synovial fluid (cellular products and fluid from blood)

37. Fig. 7.34 Joint Cavity and Synovial Fluid • Joint cavity = space within capsule and between bones • Filled with synovial fluid Functions of synovial fluid • Lubricates • Nourishes cartilage • Helps distribute stress

38. Fig. 7.34 Articular Cartilage • Hyaline cartilage • Lacks perichondrium • Use of “soft” cartilage at articulating surface reduces friction, absorbs shock, and protects the ends of the bones • Avascular • Receives nutrients by synovial fluid “washing” in and out of the cartilage during joint movements, compression and re-expansion of pressure

39. Fig. 7.34 Other Synovial Joint structures • Extrinsic Ligaments: • Dense collagenous CT structures that are separate from the joint capsule • hold bones together and possibly limit movement • Nerves • Detect pain • Proprioception—determining joint position and tension • Blood vessels • Supply cells of joint and provide some material for synovial fluid • Articular Discs • Pieces of fibrocartilage that improve fit of articularing surface thus distributing stress • Influence degree of movement at joints

40. Fig. 7.34 Other Synovial Joint structures • Bursa: • Fibrous “sacs” lined with synovial membrane and filled with synovial fluid • Reduce friction of tendons that run past/against boney angles • Can be extensions of or separate from joint capsule • Found in most major joints • Tendon Sheath • Elongated bursa around tendons • Fat pads • Provide padding and can act as space filler

41. Figure 9.5

42. Figure 9.15

43. Figure 9.5

44. Figure 9.5

45. Fig. 7.34 Arthritis: anatomical distinctions • Arthritis: inflammatory and/or degenerative disorders of joints that lead to pain and loss of joint use • Osteoarthritis • Most common • Caused by Wear and tear • Articular cartilage is worn down and bone contacts bone • Causes pain, inflammation, reduced mobility, and dysfunction • Rheumatoid Arthritis • Autoimmune disorder/Immune system attacks the synovial membrane • Tissue destruction and alteration causing joint deformation, pain, inflammation, reduced mobility and dysfunction