1. The Skeletal System

2. Skeletal System Notes
Standard SAP2b. Explain how the skeletal structures provide support and protection for tissues
EQ: How do bones and  the skeletal system function to help the body maintain homeostasis?

3. The Skeletal System Parts of the skeletal system
Bones (skeleton)
Joints
Cartilages
Ligaments
Divided into two divisions
Axial skeleton
Appendicular skeleton

4. Functions of Bones Support of the body Protection of soft organs
Movement due to attached skeletal muscles
Storage of minerals and fats
Blood cell formation

5. Bones of the Human Body The adult skeleton has 206 bones
Two basic types of bone tissue
Compact bone
Homogeneous
Spongy bone
Small needle-like pieces of bone
Many open spaces
Figure 5.2b

6. Classification of Bones on the Basis of Shape
Figure 5.1

7. Classification of Bones
Long bones
Typically longer than wide
Have a shaft with heads at both ends
Contain mostly compact bone
Examples: Femur, humerus

8. Classification of Bones
Short bones
Generally cube-shape
Contain mostly spongy bone
Examples: Carpals, tarsals

9. Classification of Bones
Flat bones
Thin and flattened
Usually curved
Thin layers of compact bone around a layer of spongy bone
Examples: Skull, ribs, sternum

10. Classification of Bones
Irregular bones
Irregular shape
Do not fit into other bone classification categories
Example: Vertebrae and hip

11. Classification of Bones on the Basis of Shape
Figure 5.1

12. Gross Anatomy of a Long Bone
Diaphysis
Shaft
Composed of compact bone
Epiphysis
Ends of the bone
Composed mostly of spongy bone
Figure 5.2a

13. Structures of a Long Bone
Periosteum
Outside covering of the diaphysis
Fibrous connective tissue membrane
Sharpey’s fibers
Secure periosteum to underlying bone
Arteries
Supply bone cells with nutrients
Figure 5.2c

14. Structures of a Long Bone
Articular cartilage
Covers the external surface of the epiphyses
Made of hyaline cartilage
Decreases friction at joint surfaces
Figure 5.2a

15. Structures of a Long Bone
Medullary cavity
Cavity of the shaft
Contains yellow marrow (mostly fat) in adults
Contains red marrow (for blood cell formation) in infants
Figure 5.2a

16. Bone Markings Sites of attachments for muscles, tendons, and ligaments
Categories of bone markings
Projections and processes – grow out from
the bone surface
Depressions or cavities – indentations

17. Summary 3-2-1 3 facts that you learned
2 things that you found interesting
1 question that you have

18. Microscopic Anatomy of Bone
Standard SAP2b. Explain how the skeletal structures provide support and protection for tissues
EQ: How does the microscopic structure of bones contribute to the functions of bones?

19. Microscopic Anatomy of Compact Bone
Osteon (Haversian System)
A unit of bone
Central (Haversian) canal
Opening in the center of an osteon
Carries blood vessels and nerves
Perforating (Volkman’s) canal
Canal perpendicular to the central canal

20. Microscopic Anatomy of Compact Bone
Figure 5.3

21. Microscopic Anatomy of Compact Bone
Lacunae
Cavities containing bone cells (osteocytes)
Arranged in concentric rings
Lamellae
Rings around the central canal
Sites of lacunae
Detail of Figure 5.3

22. Microscopic Anatomy of Compact Bone
Canaliculi
Tiny canals
Radiate from the central canal to lacunae
Form a transport system
Supply O2 and nutrients to osteocytes.

23. Microscopic Anatomy of Spongy Bone
Does not contain osteons
Consists of units called trabeculae
Irregular latticework of thin columns of bone tissue
Spaces between trabeculae filled with red marrow
In hip bones, ribs, sternum, backbone, ends of long bones.

24. Trabeculae structure

25. Summarizer
Describe the difference between compact bone and spongy bone in terms of gross and microscopic anatomy.

26. Types of Bone Cells Osteogenic Cells Unspecialized stem cells
Only bone cells that undergo cell division
Osteocytes
Mature bone cells
Osteoblasts
Bone-forming cells
Osteoclasts
Bone-destroying cells
Break down bone matrix for remodeling and release of calcium

27. Bone Formation Ossification – the process by which bones form
Bone growth occurs in 4 situations:
Initial formation in an embryo/ fetus
Growth during infancy, childhood, and adolescence until adulthood
Remodeling – replacing old tissue with new
Repair after a fracture

28. Initial Bone Formation
Skeleton begins as mesenchyme – embryonic connnective tissue that forms all other tissues
2 methods of bone formation
Intramembranous ossification
Bone forms in mesenchyme in sheet like layers
Endochondral ossification
Bone forms in hyaline cartilage made from mesenchyme

29. Intramembranous ossification
Simpler method
Forms flat bones of skull and mandible
Steps:
1. Ossification center develops – site where bone will be made
Osteoblasts secrete extracellular matrix of bone
2. Calcification – calcium and other mineral salts are deposited to harden the extracellular matrix

30. 3. Trabeculae form as the extracellular matrix hardens to form spongy bone 4. Periosteum develops from mesenchyme around the outside of bone - a layer of compact bone replaces surface layers of spongy bone

31. Endochondral Ossification

32. Bone Growth in Length Occurs at epiphyseal plate
New cartilage cells (chondrocytes) added to epiphyseal side of the plate
Old chondrocytes on diaphyseal side turn into bone tissue
Diaphyseal side increases in length

33. Bone Growth in Thickness
Osteoblasts add bone tissue to the outside
Osteoclasts break down bone on the inside
Medullary cavity enlarges as bone thickness increases

34. Bone Remodeling Ongoing process of replacing old bone tissue with new
Bone resporption – removal of minerals and collagen fibers by osteoclasts
Bone deposition - addition of minerals and collagen fibers to bone by osteoblasts

35. Bone Fractures

36. Bone Fracture Repair 1. phagocytes remove dead bone tissue
2. chonroblasts (cartilage forming cells) form cartilage at the fracture site
3. fibrocartilage converted to spongy bone
4. bone remodeling occurs -> osteoclasts absorb dead bone, spongy bone converted to compact bone
Takes longer to heal because calcium is deposited gradually