1. The Skeletal System- Osseous Tissue & Skeletal Structure Chapter 5

2. The skeletal system includes:
Bones
Cartilage
Joints
Ligaments
Other connective tissues

3. Functions of the Skeletal System
Support against gravity
Protection of soft internal organs
Movement (Leverage)
Storage
Minerals (calcium, phosphorous) – within the matrix of bone tissue
Energy reserve (adipose) – within the yellow marrow of long bones
Blood cell production – within red marrow of spongy bone tissue

4. The Structure of a Typical Bone
All bones have a combination of spongy (cancellous) & compact (dense) bone tissue

5. The Histological Features of Spongy Bone
Lamellae (layers) of matrix laid down in trabeculae - branching network of bony tissue
Osteocytes located within lacunae
Canaliculi branch out from lacunae
Many marrow cavities which contain red marrow & small blood vessels

6. The Histological Features of Compact Bone
Osteon/Haversian system - basic functional unit of compact bone
Concentric lamellae (layers) of matrix surrounding central (Haversian) canal
Osteocytes located within lacunae
Canaliculi branch out radially from lacunae
Central canals (containing BVs) run vertically down the length of the bone
Perforating (Volkmann’s) canals (containing BVs) run horizontally across the width

7. Bone Cells
In addition to Osteocytes, the mature bone cells found within the matrix of bone tissue, there are three other cells that are associated with bones
Osteoprogenitor cells
Osteoblasts
Osteoclasts

8. Bone Cells Osteoprogenitor cells Derived from mesenchymal cells
Can undergo mitosis
Mature into osteoblasts

9. Bone Cells Osteoblasts
Responsible for osteogenesis – create bone tissue
Mature into osteocytes

10. Bone Cells Osteoclasts Derived from embryological WBCs
Secrete enzymes for osteolysis – resorb/break down bone tissue
Necessary for calcium homeostasis

11. Anatomical Classification of Bones
Bones are classified by their basic shape
Flat bones
Sutural bones
Irregular bones
Long bones
Short bones
Sesamoid bones

12. Structure of a Typical Long Bone
diaphysis (compact bone)

13. The Structure of a Long Bone
diaphysis
epiphysis (spongy bone)
epiphysis

14. The Structure of a Long Bone
diaphysis
epiphysis
articular cartilage

15. The Structure of a Long Bone
epiphysis
metaphysis – location of
epiphyseal plate – in children
epiphyseal line – in adults
diaphysis
metaphysis
epiphysis
articular cartilage

16. The Structure of a Long Bone
medullary cavity
filled with yellow marrow in adults
lined with endosteum

17. The Structure of a Long Bone
Outer fibrous layer of dense irregular CT for attachment of tendons& ligaments; provides route for blood vessels & nerves; separates bone tissue from surrounding tissues
Double layered membrane surrounding bone except at articular cartilage
Inner cellular layer contains osteoprogenitor cells, osteoblasts, osteoclasts; therefore functions in bone growth & repair
periosteum

18. Bone Formation and Growth
Ossification - Process of converting other tissues to bone; begins around week 6-8 of embryological development as mesenchymal CT begins to differentiate
Two types of ossification processes occur during embryological formation:
Intramembranous
Endochondral

19. Intramembranous Ossification
Forms flat bones of skull, mandible, clavicle
Replacement of mesenchymal membrane with osseous tissue
Mesenchymal cells differentiate to osteoprogenitor cells, which then become osteoblasts
Osteoblasts create spongy bone tissue, which then remodels into compact bone where necessary
Other mesenchymal cells around the developing bone form the periosteum
Mesenchymal tissue forms
Osteoblasts begin to secrete osteoid forming spongy bone tissue
Blood vessels infiltrate tissue. Calcium salts deposit in osteoid. Periosteum develops

20. Endochondral Ossification
Most bones formed this way
Mesenchyme creates hyaline Cartilage model, which gets replaced by bone
Replacement begins in middle (diaphysis) & follows in ends (epiphyses)

21. Endochondral Ossification
Cartilage model grows in length (interstitial growth) & in width (appositional growth)
Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies.
Cartilage
model
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

22. Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies.
Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.
Enlarging
chondrocytes within
calcifying matrix
The perichondrium, which surrounded the cartilage model, now must be referred to as the periosteum.
Epiphysis
Diaphysis
Bone
formation
Cartilage
model
Figure 5.7
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

23. Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies.
Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.
Blood vessels penetrate the dying cartilage. Newly developed osteoblasts form a primary ossification center.
Enlarging
chondrocytes within
calcifying matrix
Epiphysis
Diaphysis
Marrow
cavity
Primary
ossification
center
Bone
formation
Blood
vessel
Cartilage
model
Figure 5.7
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

24. The medullary cavity begins to hollow out
Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies.
Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.
Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center.
Bone tissue continues to replace cartilage of the diaphysis, and & continues toward each epiphysis.
Enlarging
chondrocytes within
calcifying matrix
Epiphysis
Marrow
cavity
Diaphysis
Marrow
cavity
Primary
ossification
center
Blood
vessel
The medullary cavity begins to hollow out
Bone
formation
Blood
vessel
Cartilage
model
Figure 5.7
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

25. Blood vessels invade the epiphyses and osteoblasts form secondary centers of ossification.
Cartilage remains only at the ends (articular cartilage) & at metaphysis (epiphyseal plate)
Enlarging
chondrocytes within
calcifying matrix
Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies.
Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.
Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center.
The bone of the shaft thickens, and the cartilage near each epiphysis is replaced by shafts of bone.
Cartilage
model
Bone
formation
Epiphysis
Diaphysis
Marrow
cavity
Primary
ossification
center
Blood
vessel
Secondary
Epiphyseal
cartilage
Articular

26. An Overview of the Skeleton
There are 206 bones in the adult human body
Skeletal Divisions
Axial skeleton (80 bones)
Skull
Thoracic cage and sternum
Vertebral column
Appendicular skeleton (126 bones)
Upper, lower limbs
Pectoral girdle
Pelvic girdle

27. Bone Markings (Surface Features)
Table 5-1
General elevations & projections:
process
ramus
Markings for articulations:
head
condyle
facet

28. Bone Markings (Surface Features)
Spinous process
Processes for attachment:
trochanter (femur only)
tuberosity
tubercle
epicondyle
crest
line
spinous process (vertebrae only)
transverse process (vertebrae only)
Transverse process

29. Bone Markings (Surface Features)
Depressions:
fossa
sulcus
Spinous process
Transverse process
Openings:
foramen (canal)
meatus
fissure
sinus

30. Bone Markings (Surface Features)