The Skeletal System

1. The Skeletal System Chapter 6

2. Bone Function • Support • Protection • Leverage- for motion • Mineral Homeostasis • Blood cell production • Hemopoiesis in red bone marrow • Triglyceride Storage

3. Types of Bones • Long bones- longer than wide • e.g. thigh, leg, arm, forearm, fingers & toes • Short bones- almost cube shaped • Most wrist & ankle bones • Flat bones- thin & extensive surface • E.g. Cranial bones sternum, ribs & scapulae • Irregular bones- don’t fit above • E.G vertebrae and some facial bones

4. Macroscopic Structure • Parts of a long bone: • Diaphysis • Epiphysis • Metaphysis • Articular cartilage • Periosteum • Medullary cavity • Endosteum

5. Figure 6.1a

6. Figure 6.1b

7. Microscopic Structure • Matrix= • 25% water, 25% collagen fibers, 50% crystallized mineral salts • Osteogenic cells- in periosteum Osteoblasts- secrete collagen fibers- • Build matrix and become trapped in lacunae • Become osteocytes- maintain bone • Osteoclasts –formed from monocytes • Digest bone matrix for Normal bone turnover

8. Compact Bone Structure • few spaces, right below periosteum • Units = osteons (Haversian system) • Central canal- blood vessels, nerves, lymphatics • Concentric lamellae- layers of matrix • Lacunae- “lakes” contain osteocytes • Canaliculae- little canals • nutrient flow from canals and between osteocytes

9. Figure 6.2a

10. Spongy Bone • units containing trabeculae • spaces between trabeculae often contain Red Marrow • No osteons but include lacunae & canaliculae

11. Figure 6.2b

12. Bone Formation • Ossification • 1. initially in embryo & fetus • 2. Growth • 3. remodeling • 4. repair of fractures

13. Bone Formation • Mesenchyme model - replaced with bone • Intramembranous - Bone forms directly in mesenchyme layers (membrane like) • Endochondrial - forms within hyaline cartilage developed from mesenchyme

14. Intramembranous Ossification • Development of ossification center- • Cells differentiate=> osteogenic=> osteoblasts • Osteoblasts secrete organic matrix • Calcification- cells become osteocytes • In lacunae they extend cytoplasmic processes to each other • Deposit calcium & other mineral salts • Formation of trabeculae- spongy bone • Blood vessels grow in and red marrow is formed • Mesenchyme=> periosteum

15. Endochondrial Ossification • Develop a cartilage model- • Growth- chondroblasts secrete cartilage • Perichondrium forms on surface • Internal chondrocytes in lacunae die and form small cavities

16. Figure 6.3

17. Endochondrial Ossification • Ossification proceeds inward with nutrient artery from surface perichondrium • In disintegrating cartilage osteogenic cells=> osteoblasts and create a primary ossification center • As bone forms perichondrium => periosteum

18. Endochondrial Ossification • First spongy bone is formed • Osteoblasts breaks some down=> • Center develops a cavity • wall of diaphysis => compact bone • Near birth, blood vessels enter epiphysis • Secondary center is developed • Hyaline cartilage at end => articular cartilage

19. Figure 6.4

20. Growth • Length- chondrocytes in the epiphyseal plate divide and increase cartilage layer • On diaphyseal side they die and are replaced by bone • Stops during adolescence • Periosteum supports surface growth for thickness

21. Remodeling & Repair • Remodeling in response to use- • resorption by osteoclasts and deposition by osteoblasts • Repair after a fracture • Dead tissue removed • Chondroblasts => fibrocartilage • => spongy bone by osteoblasts • => remodeled to compact bone

22. Types of Fractures • Partial- incomplete break (crack) • Complete- bone in two or more pieces • Closed (simple)- not through skin • Open (compound)- broken ends break skin

23. Factors Affecting Growth • Adequate minerals (Ca, Mg, P) • Vitamins A, C, D • Hormones • Before puberty: hGH + insulin-like growth factors • Thyroid hormone & insulin also required • Sex steroids help adolescent growth spurt and cause closure of epiphyseal plate. • Weight-bearing activity

24. Calcium Homeostasis • Blood levels of Ca2+ controlled • Negative feedback loops • Parathyroid hormone => increased osteoclast activity + decreased loss in urine • Calcitonin=> decreased osteoclast activity

25. Figure 6.5

26. Exercise & Bone Tissue • Bone strengthened in response to use • Reabsorbed during disuse • e.g. Bone loss during bed rest, fractures in cast, astronauts with no gravity

27. Divisions of Skeletal System • Two divisions: axial & appendicular • Axial- around body axis • E.g. head, hyoid, ribs, sternum, & vertebrae • Appendicular- bones of upper & lower limbs plus girdles that connect them

28. Figure 6.6

29. Skull & Hyoid bone • Cranial bones: • Frontal, 2 parietal, 2 temporal, occipital, sphenoid, and ethmoid • Facial bones: • 2 nasal, 2 maxillae, 2 zygomatic, mandible, • 2 lacrimal, 2 paltine, 2 inferior nasal conchae, & the vomer

30. Figure 6.7a

31. Figure 6.7b

32. Figure 6.7c

33. Figure 6.8

34. Figure 6.9

35. Figure 6.10a

36. Figure 6.10b

37. Unique Features of Skull • Sutures- immoveable joint between skull bones • Coronal, sagittal, lambdoidal, squamous • Paranasal sinuses-cavities • Located in bones near nasal cavity • Fontanels- soft spot in fetal skull • Allow deformation at birth • Calcify to form sutures

38. Figure 6.11

39. Vertebrae • Encloses spinal cord • Supports head • Point of attachment for muscles of back, ribs and pelvic girdle • 7 cervical • 12 thoracic • 1 sacrum & 1 coccyx

40. Normal Curves in Column • 4 normal curves • Relative to front: cervical & lumbar curves are convex • Thoracic & sacral curves are concave • They increase strength, help in balance and absorb shocks

41. Figure 6.12a

42. Figure 6.12b

43. Structure of Vertebra • Body- disc-shaped front part • Vertebral arch- extends back from body • creates with the body a hole called vertebral foramen • 7 processes- • Transverse process extending laterally on each side • Spinous process extending dorsally • Two each of Superior and inferiorarticular processes- attach to neighboring vertebrae

44. Figure 6.13

45. Cervical Area • region is number from top to bottom • Cervical (C1-C7) • Spinous process often bifid and have transverse foramina on transverse process • C1- specialized to support head- called the atlas- articulates with head • Lacks body and spinous process • C2 – axis- • has body & spinous process • Also dens- that creates a pivot for head rotation

46. Figure 6.14

47. Other Vertebrae • Thoracic (T1-T12 ) • Larger than cervical • Have facets for articulating with ribs • Lumbar (L1-L5) • Largest & strongest. Processes short & thick • Sacrum (S1-S5 fused to one unit) • Foundation for pelvic girdle • Contain sacral foramina for nerves and blood vessels • Coccyx- 4 fused coccygeal vertebrae

48. Figure 6.12a

49. Figure 6.12b

50. Figure 6.15