1. Skeletal system and tissues

2. Functions of skeletal system Provide shape Protects Supports (bears body weight) Movement –Muscle attachment –joints Storage (e.g., minerals, Ca+ & PO4-) Hematopoesis (blood cell production) Requires rigidity/ability to resist compression

3. BONE TISSUE CELLS Osteoblasts: build/create matrix –Periosteum & endosteum Osteocytes: maintain matrix, provide feedback on stress experienced –In lacunae Osteoclasts: destroy matrix –In periosteum and endosteaum MATRIX Collagen: provides tensile strength (bends, twists, and pulls) –1/3 rd of matrix –organic Calcium Salts (Calcium Phosphate/hydroxyappitite): provide rigidity and compressive strength (pushes) –2/3rds of matrix –inorganic

4. Cartilage: Firm enough to hold shape and resist compression, but softer, smoother, and more flexible than bone General Characteristics Surrounded by supportive/reinforcing membrane of dense irregular CT: perichondrium Contains blood vessels Matrix –Ground substance of proteoglycans High water content  resiliency –Elastic and collagen fibers Also provides resiliency –Avascular  poor/slow repair Cells –Chondroblasts: build/create matrix In perichondrium –Chondrocytes: in lacunae lacuna chondrocyte Matrix

5. Hyaline Cartilage Most common type Ground substance ≥ fibers

6. Elastic Cartilage Most flexible Ear & larynx Elastic fibers ˃ ground substance

7. Fibrocartilage Strongest cartilage No perichondrium Collagen fibers ˃ ground substance

8. Dense Regular CT Cells: Predominantly fibroblasts Matrix: Many parallel arranged collagen fibers –Unidirectional strength Tightly packed fibers Variable amounts of elastic fibers Significant elastic fibers  elastic tissue Often Poorly vascularized Ligaments connect bone to bone

9. Elastic CT Dense Regular CT w/ enough elastic fibers to give appreciable amount of elasticity Different examples have different amounts of elasticity due to amount of elastic fibers

10. Reticular Mesh of weak reticular fibers Found in bone marrow

11. Long Bone Anatomy Long Bone as a model bone

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

13. 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

14. w/ trabeculae

17. 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

18. Locations of red marrow in adult red 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

19. Periosteum:

20. Figure 6.5

21. 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

22. Figure 6.8

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

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

25. Histology of compact bone

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

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

28. Figure 6.8

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

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

32. Central Canal: passageway for blood vessels and nerves

33. Lacunae: Spaces/cavities containing osteocytes

34. 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

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

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

37. BONE REMODELLING The process of constant creation and destruction of bone by osteoblasts and osteoclasts Bone Remodelling Continually: 1.reshapes bones in response to the specific stresses placed on them 1.Gravity 2.Muscular contraction 2.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)

38. 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

39. Fig. 11.02

40. Fig. 11.10a

41. Fig. 11.01b

42. Fig. 11.06

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

44. Fig. 7.07 Blood Ca+ decrease Blood Ca+ increase

45. Table 6.1