Chapter 5: The Skeletal System— Part A

1. Chapter 5:The Skeletal System—Part A

2. The Skeletal System • Parts of the skeletal system: • Bones (skeleton) • Joints • Cartilages • Ligaments – fibrous cords that bind bones together • Divided into two divisions: • Axial skeleton – forms longitudinal axis (down center of body) • Appendicular skeleton– limbs & girdles (attachment areas of limbs to axial skeleton)

3. Skeletal Bones 206 total bones in body 80 126

4. Functions of Bones • Support of the body • Protection of soft organs • Movement due to skeletal muscles attached by tendons • Storage of minerals (Ca & P) and fats • Blood cell formation = hematopoeisis

5. The skullprotects the brain Bones protect soft organs…

6. Muscles attach to bone for movement

7. Bones store minerals

8. Blood cell formation in bone marrow

9. Bones of the Human Body • The adult skeleton has 206 bones • Two basic types of bone tissue: • Compact bone (dense) • Homogeneous • Spongy bone • Small needle-like pieces of bone • Many open spaces Figure 5.2b

10. Compact and spongy bone

11. Classification of Bones by Shape • Four types of bone: Long Short Flat Irregular

12. Classification of Bones on the Basis of Shape Figure 5.1 Hoban

13. Classification of Bones • Long Bones • Typically longer than wide • Have a shaft with heads at both ends • Containmostly compact bone • Examples: Femur, humerus • Includes all bones of limbs except wrist & ankle

14. Femur Note the thinner shaft area and the wider heads at both ends

15. Classification of Bones • Short Bones • Generally cube-shape • Contain mostly spongy bone • Examples: Carpals (wrist), tarsals (ankle) • Sesamoidbonesfound in tendons-- ex. patella

16. Carpals

17. Classification of Bones • Flat Bones • Thin and flattened • Usually curved • Two thin layers of compact bone around a layer of spongy bone • Examples: Skull, ribs, sternum

18. Sternum and ribs

19. Classification of Bones • Irregular Bones • Irregular shape • Do not fit into other categories • Example: Vertebrae and hip

20. Lumbar vertebrae

21. Gross Anatomy of a Long Bone • Diaphysis • Shaft • Composed of compact bone • Epiphysis • Ends of the bone • Composed mostly of spongy bone covered with thin layer of compact bone • Covered with articular (glassy hyaline) cartilage Figure 5.2a

22. Structures of a Long Bone • Periosteum • Outside covering of the diaphysis • Fibrous connective tissue membrane • Sharpey’s Fibers • Secure periosteum to underlying bone • Arteries • Supply bone cells with nutrients Figure 5.2c

23. Structures of a Long Bone • Articular cartilage • Covers the external surface of the epiphyses • Made of hyaline cartilage • Decreases friction at joint surfaces Figure 5.2a

24. Anatomy of a Long Bone • Epiphyseal plate • Flat plate of hyaline cartilage seen in young, growing bone • Epiphyseal line • Remnant of the epiphyseal plate • Seen in adult bones

25. Structures of a Long Bone • Medullary Cavity • Cavity of the shaft • Contains yellow marrow (mostly fat) in adults • Contains red marrow (for blood cell formation) in infants Figure 5.2a

26. Bone Markings • Surface features of bones • Sites of attachments for muscles, tendons, and ligaments • Passages for nerves and blood vessels • Categories of bone markings • Projections and processes – grow out from the bone surface • Depressions or cavities – indentations

29. Microscopic Anatomy of Bone • Osteon(Haversian System) • A unit of bone containing central canal and matrix rings • Haversian canal, osteocytes (mature bone cell), lacunae, lamellae • Central (Haversian) canal (run lengthwise) • Opening in the center of an osteon • Carries blood vessels and nerves • Perforating (Volkman’s) canal • Canal perpendicular to the central canal • Carries blood vessels and nerves

30. Hoban

31. Microscopic Anatomy of Bone • Lacunae • Cavities containing bone cells (osteocytes) • Arranged in concentric rings • Lamellae • Rings around the central canal • Sites of lacunae Detail of Figure 5.3 Hoban

32. Canaliculi • Tiny canals • Radiating outward from central canal to lacunae • Form a transport system connecting all bone cells to a nutrient supply • Calcium salts give hardness, while collagen fibers give flexibility

33. Hoban

34. Changes in the Human Skeleton • In embryos, the skeleton is primarily hyaline cartilage • During development, much of this cartilage is replaced by bone • Cartilage remains in isolated areas • Bridge of the nose • Parts of ribs • Joints Hoban

35. Changes in the Human Skeleton • Flat bones form on fibrous membranes • Most bones develop using hyaline structures as models = ossification • Ossification • Cartilage covered with bone matrix from osteoblasts • Inner cartilage digested leaving medullary cavity • Happens by birth Hoban

36. Bone Growth (Ossification) • Epiphyseal plates allow for lengthwise growth of long bone during childhood • New cartilage is continuously formed • Older cartilage becomes ossified • Cartilage is broken down • Enclosed cartilage is digested away, opening up a medullary cavity • Bone replaces cartilage through the action of osteoblasts

37. Bone Growth (Ossification) • Bones are remodeled and lengthened until growth stops • Bones are remodeled in response to two factors • Blood calcium levels • Pull of gravity and muscles on the skeleton • Bones grow in width (called appositional growth)

38. Bone startingto replacecartilage Bone collar Hyalinecartilagemodel In an embryo (a) Long Bone Formation and Growth Figure 5.4a, step 1

39. Hyalinecartilage New center ofbone growth Medullarycavity Bone startingto replacecartilage Bloodvessels Growthin bonelength Bone collar Hyalinecartilagemodel In an embryo In a fetus (a) Long Bone Formation and Growth Figure 5.4a, step 2

40. Articularcartilage Hyalinecartilage Spongybone New center ofbone growth New boneforming Epiphysealplatecartilage Growthin bonewidth Medullarycavity Bone startingto replacecartilage Bloodvessels Growthin bonelength New boneforming Bone collar Hyalinecartilagemodel Epiphysealplate cartilage In an embryo In a fetus In a child (a) Long Bone Formation and Growth Figure 5.4a, step 3

41. Long Bone Formation and Growth Figure 5.4b

42. Types of Bone Cells • Osteocytes—mature bone cells • Osteoblasts—bone-forming cells • Osteoclasts—bone-destroyingcells • Break down bone matrix for remodeling and release of calcium in response to parathyroid hormone • Bone remodeling is performed by both osteoblasts and osteoclasts

43. Long Bone Formation & Growth • Controlled by hormones • Growth hormone • Sex hormones (puberty) • Ends during adolescence • Epiphyseal plates converted to bone

44. Hoban

45. Epiphyseal plate

46. Bone Remodeling • Process by both osteoblasts and osteoclasts • Cells regenerate in response to blood Ca levels & pull of gravity & muscles on skeleton • Osteoclasts • Stimulated by parathyroid (in throat) hormone to break down bone & release Ca to blood • Hypercalcium • Increased blood Ca causes calcium to be deposited in bone • Stress on bone • Causes bones to thicken & the projection to increase size where muscles are attached

47. Bone Remodeling

48. Bone remodeling by osteoclasts

49. Bone Formation Issue: Rickets Softened bones bow due to decreasedcalcium or decreased vitamin D (needed to absorb calcium) Results from severe malnutrition in early life Treated by increasing Calcium, Phosphorus, and Vitamin D in diet, as well as exposure to sun.