The Skeletal System

1. The Skeletal System

2. Divisions of the Skeletal System • The human skeletal system is divided into two major divisions • Axial Skeleton • Appendicular skeleton

3. Axial Skeleton The axial skeleton contains the bones of the head,neck, and torso (80 bones total)

4. appendicular skeleton The appendicular skeleton contains the bones of the upper and lower extremities (126 bones total)

5. Human Skeleton The human skeleton has a total of 206 bones in all

6. Bones Functions: Support Protection Movement Storage Blood cell formation

7. Bones Function- Support Form the internal framework that supports and anchors allsoft organs

8. Bones Function- Protection Bones protect soft body organs Ex. Skull protects brain

9. Bones Function- Movement Skeletal Muscles attach to bones by tendons Bones are used as levers to move body

10. Bones Functions-storage Fat is stored in internal cavities of bones

11. Bones Functions-storage Store minerals Most important—Calcium and phosphorus

12. Bones Functions-storage Calcium in its ion form (Ca 2+ ) must always be present in blood for nervous system to transmit messages For muscles to contract For blood to clot Bones are a storage place for Calcium

13. Bones Functions-storage Blood cell formation Hematopoiesis (formation of blood cells) occurs in the cavities of bone marrow

14. Bones Classification of bones 2 basic types of bone types Compact Bone Spongy Bone

15. Bones Compact Bone Dense Looks smooth

16. Bones Spongy Bone Small needle-like pieces of bone Lots of open space

18. Shapes of Bones Long Bones Short Bones Irregular Bones

19. Bones Long Bones Longer than they are wide Usually have a shaft with heads at both ends Mostly compact bones most bones of limbs

20. Bones Short Bones Generally cube-shaped Mostly spongy bone Ex. Patella (knee cap) , bones of wrist and ankle

21. Flat Bones Thin, flattened, usually curved Two thick layers of compact bone sandwiching a layer of spongy bone Bones of skull, ribs, sternum

22. Irregular Bones Don’t fit other categories Ex. Vertebrate, hip bone

23. Structure of a long bone Diaphysis- Shaft Makes up most of the bone’s length Composed of compact bone Covered and protected by periosteum

24. Structure of a long bone Cavity of shaft In infants- this area forms blood cells Red marrow In adults primarily filled with yellow marrow (adipose) Called yellow marrow cavity or medullary cavity Red marrow is confined to spongy bone

25. Structure of a long bone Epiphyses- the ends of the long bone Epiphyseal line Thin line spanning the epiphysis

26. Structure of a long bone Epiphyseal plate Plate of hyaline cartilage Causes the lengthwise growth of a long bone By end of puberty the plate is completely replaced by bone

27. Structure of Long Bone • Surfaces of bones aren’t smooth • Bumps, holes, and ridges • Bone markings • Reveal where muscles, tendons, and ligaments were attached • Reveal where blood vessels and nerves passed

28. Structure of Long Bone • Bone markings • Projections or processes- • Grow out from the bone surface • Depressions or cavities • Indentations in the bone

29. Structure of a long • Microscopic anatomy • Compact bone: • To the naked eye looks very dense • With microscope we see a much different picture!

30. Structure of a long • Microscopic anatomy • Compact bone • Passageways carrying nerves and blood vessels • Provides living bone with nutrients and route for waste disposal

31. Structure of Long Bone • Osteocytes • The mature bone cells • Found in cavities of the bone matrix called lacunae ( a very tough matrix)

32. Structure of Long Bone • Osteocytes • Lacunae arranged in concentric circles called lamellae • Lacunae arranged around central (Haversian) canals

33. Structure of Long Bone • Perforating (Volkmann’s) canals • Run into the compact bone at right angles to the shaft • Let the inside of bone communicate with outside

34. Bone Formation, Growth, and Remodeling • Embryo’s skeleton • Primarily hyaline cartilage • Young child • Most of cartilage has been replaced by bone • Remains in isolated areas • Bridge of nose • Parts of ribs • joints

35. Bone Formation, Growth, and Remodeling • Most bones develop using hyaline cartilage structures as their “models” • Ossification- the formation of bone

36. Bone Formation, Growth, and Remodeling • Ossification • 2 major stages • 1. hylane cartilage model is completely covered with bone by bone forming cells called osteoblasts

37. Bone Formation, Growth, and Remodeling • Ossification • Step Two: • Hyaline cartilage model is digested away • Opens up a medullary cavity within newly formed bone

38. Bone Formation, Growth, and Remodeling • By birth • Most hyaline cartilage models have been converted to bone • Excepts two reasons • Articular cartilages –cover bone ends • Epiphyseal plates

39. Bone Formation, Growth, and Remodeling • Articular cartilages • Persist for life • Reduce friction at the joint surfaces

40. Bone Formation, Growth, and Remodeling • How is the articular cartilage injured? • Trauma- twisting, sport injury • Certain diseases • Gradually over time

41. Bone Formation, Growth, and Remodeling • When there is significant loss of the articular cartilage, the knee is considered to have “arthritis”.

42. Bone Formation, Growth, and Remodeling • Epiphyseal plates • Provide for longitudinal growth of long bones during childhood • New cartilage is formed on external surface • Old cartilage is broken down and replaced by bony matrix

43. Bone Formation, Growth, and Remodeling • Epiphyseal plates • Growth controlled by hormones • Ends during adolescence, when the epiphyseal plates are completely converted to bone

44. Bone Formation, Growth, and Remodeling • How do bones widen? –called Appositional Growth • Osteoblasts in the periosteum add bone to the external face • Osteoclasts in the endosteum remove bone from inner wall

45. What happens when long bone growth ends?

46. Bone Formation, Growth, and Remodeling • Bone Remodeling • Bones continually remodeled in response to 2 factors: • 1. calcium levels in the blood • 2. the pull of gravity and muscles on the skeleton

47. Bone Formation, Growth, and Remodeling • Bone Remodeling • When blood calcium levels are low • Parathyroid hormone (PTH) is released into blood • PTH activates osteoclasts (bone destroying cells) to break down bone matrix and release calcium

48. Bone Formation, Growth, and Remodeling • Bone Remodeling • When blood calcium levels are too high (hypercalcemia) • Calcium is deposited in bone matrix as hard calcium salts

49. Bone Formation, Growth, and Remodeling • Bone Remodeling • Essential for bones to: • retain normal proportions • Strengthen as body increases size and weight

50. Bone Formation, Growth, and Remodeling • Bone Remodeling • Bedridden or physically inactive people tend to lose bone mass and atrophy • Because they aren’t subjected to stress