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 Facial bones: 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
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 inferior articular 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 ) Lumbar (L1-L5)
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

51. Figure 6.16

52. Thorax
Thoracic cage = Sternum, costal cartilages & ribs and bodies of T1-T12
Sternum- form by 3 bones that fuse by age ~25yrs
= manubrium, body, xiphoid process
Ribs- 12 pairs
1-7 articulate with sternum directly costal cartilage= true ribs

53. Figure 6.17

54. Pectoral Girdle Attach bones of upper limbs to axial skeleton
Right & left Clavicle & Scapula

55. Figure 6.18

56. Upper Limb Humerus = arm bone Articulates with scapula at shoulder
Articulates with radius & ulna at elbow
Ulna – medial bone
Radius- lateral bone (thumb side)

57. Figure 6.19

58. Figure 6.20a

59. Figure 6.20b

60. Wrist & Hand Carpus (wrist) -8 bones Metacarpals – 5 bones of hand
Number 1-5 starting with thumb
Phalanges- 14 bones of fingers
Numbered like metacarpals
each finger but the thumb has proximal, medial & distal
Thumb only proximal & distal

61. Figure 6.21

62. Pelvic Girdle Pelvic girdle includes two hip bones
Joined in front at pubic symphysis
At back- attached to sacrum = sacroiliac joint
Pelvic (hip) bone also called coxal bones

63. Figure 6.22a

64. Figure 6.22b

65. Parts of Coxal Bones 3 bones fuse by age 23 to form coxal
Ilium- largest & most superior
Ischium- lower posterior part
Pubis lower anterior part

66. Figure 6.23

67. Lower Limb Femur- thigh bone Patella = kneecap in front of knee joint
Articulates with hip proximally and
the tibia and fibula distally
Patella = kneecap in front of knee joint
Tibia- large medial, weight bearing bone of leg
Fibula- lateral to tibia and smaller

68. Figure 6.24

69. Figure 6.25

70. Ankle & Foot Tarsus (ankle) has 7 bones Metatarsals (foot bones)
Large talus (ankle bone) and
Calcaneus (heel bone)
Metatarsals (foot bones)
Numbered from medial to lateral
Phalanges (toe bones)
Big toe has proximal and distal phalanges while others have proximal, medial and distal phalanges. Numbered like metatarsals

71. Figure 6.26

72. Figure 6.27

73. Male & Female Differences
Males usually have heavier bones
Related to muscle size & strength
Female pelvis is wider and shallower than the males- allows for birth

74. Aging & Skeletal System
Birth through adolescence more bone formed than lost
Young adults- gain & loss about equal
As levels of sex steroids decline with age: bone resorption > bone formation
Bones become brittle and lose Calcium

75. Figure 6.28