1. The Skeletal System: Overview, Anatomy, and Growth
Bone Functions
Classification of Bones
Long Bone Structure
Bone Markings
Microscopic Anatomy
Bone Composition
Role of Cartilage on Bone
Bone Formation and Growth

2. Functions of Bones of the Human Body
Support
For the body and soft organs
Protection
For brain, spinal cord, and vital organs
Movement
Levers for muscle action
Storage
Minerals (calcium and phosphorus) and growth factors
Triglyceride (energy) storage in bone cavities
Blood cell formation (hematopoiesis) in marrow cavities

3. 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

4. Classification of Bones on the Basis of Type or Shape

5. The Skeletal System: Overview, Anatomy, and Growth
Bone Functions
Classification of Bones
Long Bone Structure
Bone Markings
Microscopic Anatomy
Bone Composition
Role of Cartilage on Bone
Bone Formation and Growth

6. Gross Anatomy of a Long Bone
(Sharpey’s) fibers

7. Depressions and openings
Bone Markings
Projections for muscle or
ligament attachment
Tuberosity
Crest
Trochanter
Line
Tubercle
Epicondyle
Spine
Process
Depressions and openings
Meatus
Sinus
Fossa
Groove
Fissure
Foramen
Projections for joints
Head
Facet
Condyle
Ramus

8. The Skeletal System: Overview, Anatomy, and Growth
Bone Functions
Classification of Bones
Long Bone Structure
Bone Markings
Microscopic Anatomy
Bone Composition
Role of Cartilage on Bone
Bone Formation and Growth

9. Four Types of Bone Cells
Osteogenic cell
Osteoblast
Osteocyte
Osteoclast
Mature bone cell
that maintains the
bone matrix within lacunae
Stem cell
Matrix-synthesizing
cell responsible
for bone growth, found at edge of bone
Bone-resorbing cell
Bone remodeling is a process mediated by both osteoblasts and osteoclasts
Figure 6.4a-b
Figure 6.4c-d

10. Microscopic Anatomy of Bone

11. 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

12. The Skeletal System: Overview, Anatomy, and Growth
Bone Functions
Classification of Bones
Long Bone Structure
Bone Markings
Microscopic Anatomy
Bone Composition
Role of Cartilage on Bone
Bone Formation and Growth

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

14. Chemical Composition of Bone: Inorganic
Hydroxyapatites (mineral salts)
65% of bone by mass
Mainly calcium phosphate crystals
Responsible for hardness and resistance to compression
Ca10(PO4)6(OH)2

15. Collagen provides shear and stretching strength
Bone is Contains Both Organic and Inorganic Components
Artery with
capillaries
Structures
in the
central
canal
Vein
Nerve fiber
Lamellae
Collagen
fibers
run in
different
directions
Collagen provides shear and stretching strength
Hydroxyapatite
(CaPO4) provides
compression
strength and hardness
Twisting
force

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

17. The Skeletal System: Overview, Anatomy, and Growth
Bone Functions
Classification of Bones
Long Bone Structure
Bone Markings
Microscopic Anatomy
Bone Composition
Role of Cartilage on Bone
Bone Formation and Growth

18. Skeletal Cartilages Hyaline cartilages Elastic cartilages
Provide support, flexibility, and resilience
Most abundant type
Elastic cartilages
Similar to hyaline cartilages, but contain elastic fibers
Fibrocartilages
Collagen fibers—have great tensile strength

19. Skeletal Cartilages
Contain no blood vessels or nerves
Dense connective tissue girdle of perichondrium contains blood vessels for nutrient delivery to cartilage

20. Growth of Cartilage Appositional Interstitial
Cells secrete matrix against the external face of existing cartilage
Interstitial
Chondrocytes divide and secrete new matrix, expanding cartilage from within
Calcification of cartilage occurs during
Normal bone growth
Old age

21. The Skeletal System: Overview, Anatomy, and Growth
Bone Functions
Classification of Bones
Long Bone Structure
Bone Markings
Microscopic Anatomy
Bone Composition
Role of Cartilage on Bone
Bone Formation and Growth
Intramembranous Growth
Endochondral Growth
Interstitial Growth and the Epiphyseal Plate

22. 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

23. 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

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

25. Intramembranous Ossification II
Osteoblast
Osteoid
Osteocyte
Newly calcified bone matrix
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. 2
Figure 6.8, (2 of 4)

26. Intramembranous Ossification III
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)

27. Intramembranous Ossification IV
Fibrous periosteum
Osteoblast
Plate of compact bone
Diploë (spongy bone) cavities contain red marrow
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. 4

28. Endochondral Ossification
Uses hyaline cartilage models
(a model is a structure made in the proper proportions of shape and size that can be used in forming another similar structure. Bone is formed as it destroys the model from which it’s made)
Requires breakdown of hyaline cartilage prior to ossification

29. 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

30. 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

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

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

33. 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

34. 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

35. 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

36. The Skeletal System: Overview, Anatomy, and Growth
Bone Functions
Classification of Bones
Long Bone Structure
Bone Markings
Microscopic Anatomy
Bone Composition
Role of Cartilage on Bone
Bone Formation and Growth
Intramembranous Growth
Endochondral Growth
Interstitial Growth and the Epiphyseal Plate

37. Postnatal Bone Growth: Growth of Long Bones
Articular cartilage
Epiphyseal plate
Interstitial growth:
 length of long bones
Appositional growth:
 thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces
Cartilage
grows here.
Cartilage
is replaced
by bone here.
Cartilage
grows here.
Cartilage
is replaced
by bone here.

38. Composition of the Epihyseal Plate
Epiphyseal plate cartilage organizes into four important functional zones:
Proliferation/Growth Zone (cartilage cells divide)
Hypertrophic zone (cells grow bigger)
Calcification zone (hydroxyapatite deposited)
Ossification (osteogenic) zone (where new bone is actively being formed)

39. Zones of Epiphyseal Plate Cartilage
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

40. Hormonal Regulation of Bone Growth
Growth hormone 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

41. The Skeletal System: Overview, Anatomy, and Growth
Bone Functions
Classification of Bones
Long Bone Structure
Bone Markings
Microscopic Anatomy
Bone Composition
Role of Cartilage on Bone
Bone Formation and Growth
Intramembranous Growth
Endochondral Growth
Interstitial Growth and the Epiphyseal Plate