1. Bones and Skeletal Tissues: Part A6
Bones and Skeletal Tissues: Part A

2. Contain no blood vessels or nerves
Skeletal Cartilages
Contain no blood vessels or nerves
Surrounded by dense connective tissue called perichondrium which contains blood vessels for nutrient delivery to cartilage
Hyaline cartilages
Provide support, flexibility, and resilience
Most abundant type
Articular, costal, respiratory, & nasal

3. Skeletal Cartilages Elastic cartilages Fibrocartilages
Similar to hyaline cartilages, but contain elastic fibers (more flexible)
External ear & epiglottis of larynx only
Fibrocartilages
Collagen fibers—have great tensile strength
Must withstand great pressure; knee & intervertebral discs

4. Respiratory tube cartilages in neck and thorax
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
Figure 6.1

5. Growth of Cartilage Appositional Interstitial
Cells secrete matrix against the external face of existing cartilage
Results in outward expansion due to the production of cartilage matrix on the outside of the tissue
Interstitial
Chondrocytes divide and secrete new matrix, expanding cartilage from within
Results in expansion from within the cartilage matrix due to division of lacunae-bound chondrocytes and secretion of matrix.
Calcification of cartilage occurs during normal bone growth and old age.

6. Two main groups, by location
Bones of the Skeleton
Two main groups, by location
Axial skeleton (brown)
the skull, vertebral column, and rib cage
Appendicular skeleton (yellow)
bones of the upper and lower limbs & the girdles that attach them to the axial skeleton

7. Cartilage in Cartilages in external ear nose Articular Cartilage
of a joint
Cartilage in
Intervertebral disc
Costal
cartilage
Pubic
symphysis
Meniscus (padlike
cartilage in
knee joint)
Articular cartilage
of a joint
Figure 6.1

8. Classification of Bones by Shape
Long bones
Longer than they are wide
definite shaft and two ends
all limb bones except patellas, carpals, and tarsals.
Short bones
Cube-shaped bones
carpals and tarsals (in wrist and ankle)
Sesamoid bones (within tendons, e.g., patella)

9. Classification of Bones by Shape
Flat bones
Thin, flat, slightly curved
most skull bones, the sternum, scapulae, and ribs.
Irregular bones
Complicated shapes that do not fit in any other class
vertebrae and coxae

10. Figure 6.2

11. Functions of Bones Support Protection Movement
For the body and soft organs
Protection
For brain, spinal cord, and vital organs
Movement
Levers for muscle action

12. Functions of Bones Storage
Minerals (calcium and phosphorus) and growth factors
Blood cell formation (hematopoiesis) in marrow cavities
Triglyceride (energy) storage in bone cavities

13. Gross Anatomy: Bone Markings
Bulges, depressions, and holes serve as
Sites of attachment for muscles, ligaments, and tendons
Joint surfaces
Conduits for blood vessels and nerves

14. Bone Markings: Projections
Sites of muscle and ligament attachment
Tuberosity—rounded projection
Crest—narrow, prominent ridge
Trochanter—large, blunt, irregular surface
Line—narrow ridge of bone
Tubercle—small rounded projection
Epicondyle—raised area above a condyle
Spine—sharp, slender projection
Process—any bony prominence

15. Table 6.1

16. Bone Markings: Projections
Projections that help to form joints
Head
Bony expansion carried on a narrow neck
Facet
Smooth, nearly flat articular surface
Condyle
Rounded articular projection
Ramus
Armlike bar

17. Table 6.1

18. Bone Markings: Depressions and Openings
Meatus
Canal-like passageway
Sinus
Cavity within a bone
Fossa
Shallow, basinlike depression
Groove
Furrow
Fissure
Narrow, slitlike opening
Foramen
Round or oval opening through a bone

19. Table 6.1

20. Spongy (cancellous) bone
Bone Textures
Compact bone
Dense outer layer
Appears smooth & solid
Spongy (cancellous) bone
Honeycomb of trabeculae (needle-like or flat pieces)
Internal

21. Structure of a Long Bone
Diaphysis (tubular shaft)
Compact bone collar surrounds medullary (marrow) cavity
Medullary cavity in adults contains fat (yellow marrow)

22. Structure of a Long Bone
Epiphyses
Expanded ends
Spongy bone interior
Outer layer of compact bone
Epiphyseal line- between diaphysis & epiphyses; remnant of growth (epiphyseal) plate
Articular (hyaline) cartilage on joint surfaces

23. Articular cartilage Compact bone Proximal epiphysis Spongy bone
Epiphyseal
line
Periosteum
Compact bone
Medullary
cavity (lined
by endosteum)
(b)
Diaphysis
Distal
epiphysis
(a)
Figure 6.3a-b

24. Membranes of Bone Periosteum
Outer fibrous layer that covers the external surface
Inner osteogenic layer
Osteoblasts (bone-forming cells)
Osteoclasts (bone-destroying cells)
Osteogenic cells (stem cells)
Nerve fibers, nutrient blood vessels, and lymphatic vessels enter the bone via nutrient foramina
Secured to underlying bone by Sharpey’s fibers

25. Membranes of Bone Endosteum Internal connective tissue covering
Delicate membrane on internal surfaces of bone
Also contains osteoblasts and osteoclasts

26. Endosteum Yellow bone marrow Compact bone Periosteum Perforating
(Sharpey’s) fibers
Nutrient
arteries
(c)
Figure 6.3c

27. Structure of Short, Irregular, and Flat Bones
Periosteum-covered compact bone on the outside
Endosteum-covered spongy bone within
Spongy bone called diploë in flat bones
Bone marrow between the trabeculae (endosteum)

28. Spongy bone
(diploë)
Compact
bone
Trabeculae
Figure 6.5

29. Location of Hematopoietic Tissue (Red Marrow)
Red marrow cavities of adults
Trabecular cavities of the heads of the femur and humerus (epiphyses in long bones)
Trabecular cavities of the diploë (spongy) of flat bones
Red marrow of newborn infants
Medullary cavities and all spaces in spongy bone (all flat bones, epiphyses, and medullary cavities)

30. Microscopic Anatomy of Bone
Cells of bones
Osteogenic (osteoprogenitor) cells
Stem cells in periosteum and endosteum that give rise to osteoblasts
Osteoblasts
Bone-forming cells

31. (a) Osteogenic cell (b) Osteoblast Stem cell Matrix-synthesizing
cell responsible
for bone growth
Figure 6.4a-b

32. Microscopic Anatomy of Bone
Cells of bone
Osteocytes
Mature bone cells
Osteoclasts
Cells that break down (resorb) bone matrix

33. (c) Osteocyte (d) Osteoclast Mature bone cell that maintains the
bone matrix
Bone-resorbing cell
Figure 6.4c-d

34. Microscopic Anatomy of Bone: Compact Bone
Haversian system, or osteon—structural unit of compact bone
Lamellae
Weight-bearing
Column-like matrix tubes
Surrounds Haversian canal
Central (Haversian) canal
Contains blood vessels and nerves

35. Artery with capillaries Structures in the Vein central canal
Nerve fiber
Lamellae
Collagen
fibers
run in
different
directions
Twisting
force
Figure 6.6

36. Microscopic Anatomy of Bone: Compact Bone
Perforating (Volkmann’s) canals
At right angles to the central canal (long axis)
Connects blood vessels and nerves of the periosteum and central canal
Lacunae—small cavities that contain osteocytes
Canaliculi—hairlike canals that connect lacunae to each other and the central canal

37. Microscopic Anatomy of Bone: Compact Bone
Circumferential lamellae are located just beneath the periosteum, extending around the entire circumference of the bone
Interstitial lamellae lie between intact osteons, filling the spaces in between

38. 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)
Figure 6.7a-c

39. Microscopic Anatomy of Bone: Spongy Bone
Trabeculae
Align along lines of stress
No osteons
Contain irregularly arranged lamellae, osteocytes, and canaliculi
Capillaries in endosteum supply nutrients

40. Nerve Vein Lamellae Artery Central canal Canaliculus Osteocyte Lacunae
in a lacuna
Lacunae
(b)
Figure 6.3b

41. Chemical Composition of Bone: Organic
Cells: Osteogenic cells, osteoblasts, osteocytes, osteoclasts
Osteoid—organic bone matrix secreted by osteoblasts
Ground substance (proteoglycans, glycoproteins)
Collagen fibers
Provide tensile strength and flexibility

42. Chemical Composition of Bone: Inorganic
Hydroxyapatites (mineral salts)
65% of bone by mass
Mainly calcium phosphate crystals
Responsible for hardness and resistance to compression

43. Osteogenesis (ossification)—bone tissue formation
Bone Development
Osteogenesis (ossification)—bone tissue formation
Stages
Bone formation—begins in the 2nd month of development
Postnatal bone growth—until early adulthood
Bone remodeling and repair—lifelong

44. Two Types of Ossification
Intramembranous ossification
Membrane bone develops from fibrous membrane
Forms flat bones, e.g. clavicles and cranial bones
Endochondral ossification
Cartilage (endochondral) bone forms by replacing hyaline cartilage
Forms most of the rest of the skeleton

45. Mesenchymal cell Collagen fiber Ossification center Osteoid Osteoblast1
Ossification centers appear in the fibrous connective tissue membrane.
• Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center.
Figure 6.8, (1 of 4)

46. Newly calcified bone matrix
Osteoblast
Osteoid
Osteocyte
Newly calcified bone matrix 2
Bone matrix (osteoid) is secreted within the fibrous membrane and calcifies. • Osteoblasts begin to secrete osteoid, which is calcified within a few days.
• Trapped osteoblasts become osteocytes.
Figure 6.8, (2 of 4)

47. Mesenchyme condensing to form the periosteum
Trabeculae of woven bone
Blood vessel 3
Woven bone and periosteum form. • Accumulating osteoid is laid down between embryonic blood vessels in a random manner. The result is a network (instead of lamellae) of trabeculae called woven bone.
• Vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum.
Figure 6.8, (3 of 4)

48. Diploë (spongy bone) cavities contain red marrow
Fibrous periosteum
Osteoblast
Plate of compact bone
Diploë (spongy bone) cavities contain red marrow 4
Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears.
• Trabeculae just deep to the periosteum thicken, and are later replaced with mature lamellar bone, forming compact bone plates.
• Spongy bone (diploë), consisting of distinct trabeculae, per- sists internally and its vascular tissue becomes red marrow.
Figure 6.8, (4 of 4)

49. Endochondral Ossification
Uses hyaline cartilage models
Requires breakdown of hyaline cartilage prior to ossification

50. Childhood to adolescence
Week 9
Month 3
Birth
Childhood to adolescence
Articular cartilage
Secondary ossification center
Spongy bone
Epiphyseal blood vessel
Area of deteriorating cartilage matrix
Epiphyseal plate cartilage
Hyaline cartilage
Medullary cavity
Spongy bone formation
Bone collar
Blood vessel of periosteal bud
Primary ossification center 1
Bone collar forms around hyaline cartilage model.
Cartilage in the center of the diaphysis calcifies and then develops cavities. 2
The periosteal bud inavades the internal cavities and spongy bone begins to form. 3
The diaphysis elongates and a medullary cavity forms as ossification continues. Secondary ossification centers appear in the epiphyses in preparation for stage 5. 4
The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages. 5
Figure 6.9

51. Primary ossification center
Week 9
Hyaline cartilage
Bone collar
Primary ossification center
Bone collar forms around hyaline cartilage model. 1
Figure 6.9, step 1

52. Area of deteriorating cartilage matrix2
Cartilage in the center of the diaphysis calcifies and then develops cavities.
Figure 6.9, step 2

53. Blood vessel of periosteal bud
Month 3
Spongy bone formation
Blood vessel of periosteal bud 3
The periosteal bud inavades the internal cavities and spongy bone begins to form.
Figure 6.9, step 3

54. Epiphyseal blood vessel Secondary ossification center
Birth
Epiphyseal blood vessel
Secondary ossification center
Medullary cavity
The diaphysis elongates and a medullary cavity forms as ossification continues. Secondary ossification centers appear in the epiphyses in preparation for stage 5. 4
Figure 6.9, step 4

55. Childhood to adolescence
Articular cartilage
Spongy bone
Epiphyseal plate cartilage
The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages. 5
Figure 6.9, step 5

56. Childhood to adolescence
Week 9
Month 3
Birth
Childhood to adolescence
Articular cartilage
Secondary ossification center
Spongy bone
Epiphyseal blood vessel
Area of deteriorating cartilage matrix
Epiphyseal plate cartilage
Hyaline cartilage
Medullary cavity
Spongy bone formation
Bone collar
Blood vessel of periosteal bud
Primary ossification center 1
Bone collar forms around hyaline cartilage model.
Cartilage in the center of the diaphysis calcifies and then develops cavities. 2
The periosteal bud inavades the internal cavities and spongy bone begins to form. 3
The diaphysis elongates and a medullary cavity forms as ossification continues. Secondary ossification centers appear in the epiphyses in preparation for stage 5. 4
The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages. 5
Figure 6.9

57. Postnatal Bone Growth Interstitial growth:  length of long bones
Occurs at ossification zone
rapid division of the upper cells in the columns of chondrocytes
calcification and deterioration of cartilage at the bottom of the columns
replacement by bone tissue

58. Growth in Length of Long Bones
Appositional growth:
 thickness & width
deposition of bone matrix by osteoblasts beneath the periosteum
Epiphyseal plate cartilage organizes into four important functional zones:
Proliferation (growth)
Hypertrophic
Calcification
Ossification (osteogenic)

59. Cartilage cells undergo mitosis.
Resting zone
Proliferation zone
Cartilage cells undergo
mitosis. 1
Hypertrophic zone
Older cartilage cells
enlarge. 2
Calcification zone
Matrix becomes calcified;
cartilage cells die; matrix
begins deteriorating. 3
Calcified cartilage
spicule
Osteoblast depositing
bone matrix
Ossification zone
New bone formation is
occurring.
Osseous tissue
(bone) covering
cartilage spicules 4
Figure 6.10

60. Hormonal Regulation of Bone Growth
Growth hormone from the anterior pituitary stimulates epiphyseal plate activity
Thyroid hormone modulates activity of growth hormone
Testosterone and estrogens (at puberty)
Promote adolescent growth spurts
End growth by inducing epiphyseal plate closure

61. Bone growth 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.
Figure 6.11

62. Bone Deposit
Bone remodeling: balanced bone deposit and removal
Occurs where bone is injured or added strength is needed
Requires a diet rich in protein; vitamins C, D, and A; calcium; phosphorus; magnesium; and manganese

63. Sites of new matrix deposit are revealed by the
Bone Deposit
Sites of new matrix deposit are revealed by the
Osteoid seam
Unmineralized band of matrix
Calcification front
The abrupt transition zone between the osteoid seam and the older mineralized bone

64. Bone Resorption Osteoclasts secrete
Lysosomal enzymes (digest organic matrix)
Acids (convert calcium salts into soluble forms)
Dissolved matrix is transcytosed across osteoclast, enters interstitial fluid and then blood

65. What controls continual remodeling of bone?
Control of Remodeling
What controls continual remodeling of bone?
Hormonal mechanisms that maintain calcium homeostasis in the blood
Mechanical stress and gravitational forces

66. Hormonal Control of Blood Ca2+
Calcium is necessary for
Transmission of nerve impulses
Muscle contraction
Blood coagulation
Secretion by glands and nerve cells
Cell division

67. Hormonal Control of Blood Ca2+
Primarily controlled by parathyroid hormone (PTH)
 Blood Ca2+ levels 
Parathyroid glands release PTH
PTH stimulates osteoclasts to degrade bone matrix and release Ca2+
 Blood Ca2+ levels

68. Stimulus Thyroid gland Osteoclasts Parathyroid degrade bone glands
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
Figure 6.12

69. Hormonal Control of Blood Ca2+
May be affected to a lesser extent by calcitonin
 Blood Ca2+ levels 
Parafollicular cells of thyroid release calcitonin
Osteoblasts deposit calcium salts
 Blood Ca2+ levels
Leptin has also been shown to influence bone density by inhibiting osteoblasts

70. Response to Mechanical Stress
Wolff’s law: A bone grows or remodels in response to forces or demands placed upon it
Observations supporting Wolff’s law:
Handedness (right or left handed) results in bone of one upper limb being thicker and stronger
Curved bones are thickest where they are most likely to buckle
Trabeculae form along lines of stress
Large, bony projections occur where heavy, active muscles attach

71. Load here (body weight)
Head of
femur
Tension
here
Compression
here
Point of
no stress
Figure 6.13

72. Classification of Bone Fractures
Bone fractures may be classified by four “either/or” classifications:
Position of bone ends after fracture:
Nondisplaced—ends retain normal position
Displaced—ends out of normal alignment
Completeness of the break
Complete—broken all the way through
Incomplete—not broken all the way through

73. Classification of Bone Fractures
Orientation of the break to the long axis of the bone:
Linear—parallel to long axis of the bone
Transverse—perpendicular to long axis of the bone
Whether or not the bone ends penetrate the skin:
Compound (open)—bone ends penetrate the skin
Simple (closed)—bone ends do not penetrate the skin

74. Common Types of Fractures
All fractures can be described in terms of
Location
External appearance
Nature of the break

75. Table 6.2

76. Table 6.2

77. Table 6.2

78. Stages in the Healing of a Bone Fracture
Hematoma forms
Torn blood vessels hemorrhage
Clot (hematoma) forms
Site becomes swollen, painful, and inflamed

79. Hematoma 1
A hematoma forms.
Figure 6.15, step 1

80. Stages in the Healing of a Bone Fracture
Fibrocartilaginous callus forms
Phagocytic cells clear debris
Osteoblasts begin forming spongy bone within 1 week
Fibroblasts secrete collagen fibers to connect bone ends
Mass of repair tissue now called fibrocartilaginous callus

81. 2 External callus Internal callus (fibrous tissue and cartilage)
New blood vessels
Spongy bone trabecula
Fibrocartilaginous callus forms. 2
Figure 6.15, step 2

82. Stages in the Healing of a Bone Fracture
Bony callus formation
New trabeculae form a bony (hard) callus
Bony callus formation continues until firm union is formed in ~2 months

83. Bony callus of spongy bone3
Bony callus forms.
Figure 6.15, step 3

84. Stages in the Healing of a Bone Fracture
Bone remodeling of callus
In response to mechanical stressors over several months
Final structure resembles original

85. Healed fracture 4
Bone remodeling occurs.
Figure 6.15, step 4

86. Bony callus of spongy bone
Hematoma
External callus
Bony callus of spongy bone
Internal callus (fibrous tissue and cartilage)
New blood vessels
Healed fracture
Spongy bone trabecula 1
A hematoma forms. 2
Fibrocartilaginous callus forms. 3
Bony callus forms. 4
Bone remodeling occurs.
Figure 6.15

87. Homeostatic Imbalances
Osteomalacia and rickets
bone is inadequately mineralized
Calcium salts not deposited
Rickets (childhood disease) causes bowed legs and other bone deformities
Cause: vitamin D deficiency or insufficient dietary calcium

88. Homeostatic Imbalances
Osteoporosis
Normal matrix but loss of bone mass—bone resorption outpaces deposit
bones become more porous and lighter, increasing the likelihood of fractures
Spongy bone of spine and neck of femur become most susceptible to fracture
Risk factors
Lack of estrogen (older women:menopause), calcium or vitamin D; petite body form; immobility; low levels of TSH; diabetes mellitus

89. Figure 6.16

90. Osteoporosis: Treatment and Prevention
Calcium, vitamin D, and fluoride supplements
 Weight-bearing exercise throughout life
Hormone (estrogen) replacement therapy (HRT) slows bone loss
Some drugs (Fosamax, SERMs, statins) increase bone mineral density

91. Paget’s Disease
Excessive and haphazard bone formation and breakdown, usually in spine, pelvis, femur, or skull
Pagetic bone has very high ratio of spongy to compact bone and reduced mineralization
Unknown cause (possibly viral)
Bone deformation
Treatment includes calcitonin and biphosphonates

92. Developmental Aspects of Bones
The skeleton derives from embryonic mesenchymal cells
Embryonic skeleton ossifies predictably so fetal age easily determined from X rays or sonograms
At birth (12 weeks gestation), most long bones are well ossified (except epiphyses…form secondary ossification centers)

93. Parietal bone Occipital bone Frontal bone of skull Mandible Clavicle
Scapula
Radius
Ulna
Ribs
Humerus
Vertebra
Ilium
Tibia
Femur
Figure 6.17

94. Developmental Aspects of Bones
Throughout childhood, bone growth exceeds bone resorption; in young adults, these processes are in balance.
Nearly all bones completely ossified by age 25
Bone mass decreases with age beginning in 4th decade
Rate of loss determined by genetics and environmental factors
In old age, bone resorption predominates