1. Introduction to the Skeleton

2. Bones and Skeletal Tissue
The human skeleton is made of both cartilage and bone tissue.
An infant’s skeleton is primarily cartilage but as the infants grows it is replaced by bone.

3. Figure 6.17 Fetal primary ossification centers at 12 weeks.
Parietal bone
Occipital bone
Frontal bone
of skull
Mandible
Clavicle
Scapula
Radius
Ulna
Ribs
Humerus
Vertebra
Ilium
Tibia
Femur

4. Skeletal Cartilage
Cartilage consists primarily of water. This provides resilience and compressibility that protects the bones.
There are three types:

5. Skeletal Cartilage
Cartilage consists primarily of water. This provides resilience and compressibility that protects the bones.
There are three types:
Hyaline
Elastic
Fibrocartilage

6. Hyaline Cartilage Most abundant Chondrocytes appear spherical
Collagen is the only fiber
Locations:
Articular cartilage
Costal cartilage
Respiratory cartilage
Nasal cartilage

7. Fibro elastic Cartilage
Very compressible, chondrocytes are found in parallel rows
Found only in vertebral discs and meniscus of the knee.

8. Elastic Cartilage Similar to hyaline but contains elastic fibers
Found in areas where there is repeated bending
Two locations:
External ear
Epiglottis

9. Figure 6.1 The bones and cartilages of the human skeleton.
Epiglottis
Larynx
Thyroid
cartilage
Cartilage in
external ear
Cartilages in
nose
Trachea
Cricoid
cartilage
Lung
Articular
Cartilage
of a joint
Cartilage in
Intervertebral disc
Costal
cartilage
Respiratory tube cartilages
in neck and thorax
Pubic
symphysis
Bones of skeleton
Axial skeleton
Meniscus (padlike
cartilage in
knee joint)
Appendicular skeleton
Cartilages
Articular cartilage
of a joint
Hyaline cartilages
Elastic cartilages
Fibrocartilages

10. Perichondrium
This supplies nutrients via diffusion to the avascular cartilage.
This limits the thickness of the cartilage.

11. Chondrocytes
The chondrocyte is the cell responsible for the maintenance and growth of the cartilage.
They reside in lacunae

12. Cartilage can grow two ways:
Cartilage Growth
Cartilage can grow two ways:
Appositional growth
Interstitial growth

13. Appositional Growth
Appositional growth (from the edges) occurs where cells from the perichondrium lay down new a cartilage matrix.

14. Interstitial Growth
Growth from inside the cartilage. The chondrocytes divide in the lacunae laying down more matrix.

15. Skeletal Classification
There are 206 bones in the adult skeleton.

16. Skeletal Classification
The skeleton is divided into the:
Axial Skeleton
Appendicular Skeleton

17. Axial Skeleton Forms the long axis of the body.
Its primary roll is support and protection of the organs.

18. Appendicular Skeleton
Bones of the upper and lower limbs including the shoulder and hips. It is involved in locomotion.

19. Bones are further classified by shape. There are 4 types:
Bone Classification
Bones are further classified by shape.
There are 4 types:
Long Bones
Short Bones
Flat Bones
Irregular Bones

20. Long Bones
Are longer than wide. It consists of a shaft plus two ends.

21. Long Bones Are longer than wide. It consists of a shaft plus two ends.
Found on the Appendicular Skeleton.

22. Long Bones Are longer than wide. It consists of a shaft plus two ends.
Found on the Appendicular Skeleton.
Size doesn’t matter
Femur vs phalanges

23. Short Bones
Typically cube shape. These are found on the wrist (carpals) and ankle (tarsals)

24. Flat Bones Are flat and thin in 1 dimension. Often have a curve edge
Examples include ribs, scapula and skull

25. Irregular Shape
No specific shape, examples include the pelvic bones and vertebrae.

26. Figure 6.2 Classification of bones on the basis of shape.
Flat bone
(sternum)
(a)
Long bone
(humerus)
(b)
Irregular bone
(vertebra), right
lateral view
(d)
Short bone
(talus)

27. Function of the Skeletal System
Support- respiration
Protection-skull
Movement-Appendicular skeleton
Mineral Storage-calcium phosphate
Blood Cell Formation- Hematopoiesis
Fat Storage

28. Gross anatomy of Bone
The surface of the bone is covered by projections and ridges that serve as attachment points for ligaments and tendons.
Examples include:
Trochanters
Spines &
Grooves

30. Gross anatomy of Bone
Bone is can be classified as compact or spongy bone.

31. Gross anatomy of Bone
Compact bone is dense and has a smooth outer surface.

32. Gross anatomy of Bone
Spongy bone has a honey comb structure made up of small projections called trabeculae.

33. Structure of the long bone
Diaphysis is the long central shaft of a long bone

34. Structure of the long bone
Diaphysis is the long central shaft of a long bone
Epiphyses are the ends of the bone

35. Structure of the long bone
Diaphysis is the long central shaft of a long bone
Epiphyses are the ends of the bone
Membranes cover the exterior and interior of the bones

36. Structure of the long bone
Diaphysis is the long central shaft of a long bone
Epiphyses are the ends of the bone
Membranes cover the exterior and interior of the bones
Composed both of compact and spongy bone

37. Structure of the long bone
The diaphysis has a large central cavity and is filled with fat (yellow marrow).

38. Structure of the long bone
The epiphyses are filled with hematopoietic tissue (red marrow) which gives rise to the blood cells.

39. Structure of the long bone
The periosteum covers the exterior of the bone.
It contains bone forming cells and is involved with bone growing wider.

40. Articular
cartilage
Proximal epiphysis
Spongy bone
Epiphyseal line
Periosteum
Compact bone
Medullary
cavity (lined
by endosteum)
Diaphysis
Distal epiphysis
(a)

41. Figure 6.3c The structure of a long bone (humerus of arm).
Endosteum
Yellow
bone marrow
Compact bone
Periosteum
Perforating
(Sharpey’s) fibers
Nutrient
arteries
(c)

42. Microscopic Anatomy of Bone
Four cell types populate the bone tissues.
These are:
Osteogenic cells
Osteoblasts
Osteocytes
Osteoclasts

43. Microscopic Anatomy of Bone
Osteogenic cells are stem cells that give rise to other bone forming cells

44. Microscopic Anatomy of Bone
Osteoblasts are bone forming cells
Osteocytes maintains the bone matrix
Osteoclasts destroy bone

45. Figure 6.4 Comparison of different types of bone cells.
(a) Osteogenic cell
(b) Osteoblast
(c) Osteocyte
(d) Osteoclast
Stem cell
Matrix-synthesizing
cell responsible
for bone growth
Mature bone cell
that maintains the
bone matrix
Bone-resorbing cell

46. Microscopic Anatomy Compact Bone
The structural unit of the compact bone is the osteon or Haversian System.
It consists of a central canal that contains blood vessels and nerves.

47. Microscopic Anatomy Compact Bone
Branches from the nerves and blood vessels go transversely through Volkmann's canals.

48. Figure 6.7 Microscopic anatomy of compact bone.
Spongy bone
Central
(Haversian) canal
Perforating
(Volkmann’s) canal
Endosteum lining bony canals
and covering trabeculae
Osteon
(Haversian system)
Circumferential
lamellae
(a)
Perforating (Sharpey’s) fibers
Lamellae
Periosteal blood vessel
Periosteum
Nerve
Vein
Artery
Lamellae
Central
canal
Canaliculi
Lacuna (with
osteocyte)
Osteocyte
in a lacuna
Lacunae
Interstitial lamellae
(b)
(c)

49. Microscopic Anatomy Compact Bone
Osteocytes are found in the lacunae.

50. Figure 6.7c Microscopic anatomy of compact bone.
Lacuna (with
osteocyte)
Lamellae
Central
canal
Lacunae
Interstitial lamellae
(c)

51. Bone Formation (Remodeling)
Bone has an inorganic and organic component.
The inorganic component is calcium phosphate.
The organic component is made up of collagen and proteoglycans.

52. Bone Formation (Remodeling)
Bone is unique because is can repair itself and adjust to mechanical stresses.

53. Bone Formation (Remodeling)
Bone is unique because is can repair itself and adjust to mechanical stresses.
This is a complex process involving a tug of war between Osteoclasts and Osteoblasts.

54. Bone Formation (Remodeling)
Hormones such as Calcitonin (PHT), sex and growth hormones and vitamins such as Vitamin D are involved in this process.

55. Figure 6.12 Parathyroid hormone (PTH) control of blood calcium levels.
Calcium homeostasis of blood: 9–11 mg/100 ml
BALANCE
BALANCE
Stimulus
Falling blood
Ca2+ levels
Thyroid
gland
Osteoclasts
degrade bone
matrix and
release Ca2+
into blood.
Parathyroid
glands
Parathyroid
glands release
parathyroid
hormone (PTH).
PTH

56. Bone Formation (Remodeling)
Wolf’s law governs how a bone remodels.
Compression and tension work together to shape a bone.
For example, a person’s dominate arm has a thicker bone structure.

57. Figure 6.13 Bone anatomy and bending stress.
Load here (body weight)
Head of
femur
Tension
here
Compression
here
Point of
no stress

58. (a) Cross- sectional dimension of the humerus Added bone matrix
Figure Vigorous exercise can lead to large increases in bone strength.
(a)
Cross-
sectional
dimension of
the humerus
Added
bone matrix
counteracts
added stress
(b) Serving arm
Nonserving arm

59. Bone Formation (Remodeling)
Bones can grow two ways:
1) Longitudinal growth occurs in long bones between the diaphysis and epiphysis, along a region called the epiphyseal plate.
Cartilage expands and is replaced by bone.

60. Bone Formation (Remodeling)
Bones can grow two ways:
2) Appositional growth (width) occurs between the periosteum and endosteum.

61. Figure 6.11 Long bone growth and remodeling during youth.
Bone remodeling
Articular cartilage
Cartilage
grows here.
Epiphyseal plate
Cartilage
is replaced
by bone here.
Bone is
resorbed here.
Cartilage
grows here.
Bone is added
by appositional
growth here.
Cartilage
is replaced
by bone here.
Bone is
resorbed here.

62. Diseases & Injuries of the Bone
Fractures are the most common injury to bone. Most fractures will heal with time.

63. Diseases & Injuries of the Bone
Fractures are the most common injury to bone. Most fractures will heal with time.

64. Diseases & Injuries of the Bone

65. Diseases & Injuries of the Bone

66. Table 6.2 Common Types of Fractures (1 of 3)

67. Table 6.2 Common Types of Fractures (2 of 3)

68. Table 6.2 Common Types of Fractures (3 of 3)

69. Diseases & Injuries of the Bone
Osteoporosis is a disease of old age and is a major cause of hip fractures. The bone mass decreases. It is typically diagnosed with a bone density test.

70. Figure 6.16 The contrasting architecture of normal versus osteporotic bone.

71. Diseases & Injuries of the Bone

73. Diseases & Injuries of the Bone
Rickets and Osteomalacia results in soft bones. Ricketts is a child hood disease while Osteomalacia is in adults.
Rickets is often due to a Vitamin D deficiency.

74. Diseases & Injuries of the Bone