1. The Skeletal System: Bone Tissue

2. Bone Tissue Bone is made up of several different tissues :
Bone, cartilage, dense connective tissue, epithelium, blood forming tissues, adipose tissue, and nervous tissue.
Each individual bone is an organ: bones along with their cartilages make up the skeletal system.

3. Functions of Skeletal System
Structural framework of body
Protection of organs
Assist with movement
Hemopoiesis = blood cell formation (marrow)
E. Yellow marrow = site of triglyceride (fat) storage

4. Structure of Bone Diaphysis Shaft of long bone Epiphysis Ends of bone
Metaphyses
Areas between epiphysis and diaphysis and include epiphyseal plates (growth plates)

5. Structure of Bone
Hyaline cartilage = ends of bones to reduce friction and absorb shock at joints
Periosteum = hard covering of bone that protects, assists in fracture repair, nourishes bone, and serves as an attachment point for tendons and ligaments
Marrow cavity = space within diaphysis
Endosteum = lining of marrow cavity

6. Histology of Bone Tissue

7. Four Principal Types of Bone Cells
Osteogenic cells = undergo cell division and develop into osteoblasts
Osteoblasts = bone-building cells
Osteocytes = mature bone cells
Osteoclasts = serve to break down bone tissue

8. Four Principal Types of Bone Cells

9. Bone Matrix
Contain inorganic salts (hydroxyapatite, calcium carbonate) and collagen fibers
Mineral salts confer hardness on bone while collagen fibers give bone its great tensile strength.

10. Compact vs Spongy Bone

11. Compact Bone Arranged in units called Haversian sytems (osteons)
Contain blood vessels and nerves
Aligned in same direction along paths of stress

12. Spongy Bone Does not contain osteons
Forms most of the short, flat, and irregular bones and epiphyses of long bones
Supports/protects red bone marrow

13. Bone is richly supplied with blood.
Blood Supply of Bone
Bone is richly supplied with blood.

14. Arterial Supply Periosteal Arteries
Pass through Volkmann’s canals (penetrating canals into compact bone) in which they supply the eriostemon and the outer layer of compact bone with blood.

15. Arterial Supply
Nutrient artery = passes through the nutrient canal of a bone (nutrient foramen) and sends branches into the central Haversian canals to provide for osteocytes.
Epiphyseal artery = artery that supplies the bone marrow with blood (extension of nutrient artery).

16. Bone Development

17. Intramembranous Ossification
Formation of all flat bones and jaw

18. Intramembranous Ossification
During development membrane-like layers of connective tissues appear at the site of future bones.
Then some primitive connective tissue cells enlarge and differentiate into bone-forming cells called osteoblasts.
Osteoblasts become active in membrane and deposit bony matrix around them.
Cells of the membranous tissues that are outside the developing bone give rise to the periosteum.
5. Osteoblasts on the inside of the periosteum form a layer of compact bone over the surface of the newly formed spongy bone.

19. Intramembranous Ossification

20. Endochondral Ossification
Replacement of cartilage with bone

21. Endochondral Ossification
Development of cartilage model (Hyaline cartilage)
- At site where bone is going to form, mesenchymal cells crowd together in the shape of future bone, perichondrium forms here.
2. Growth of Cartilage Model
- Chondrocytes grow and secrete more matrix

22. Endochondral Ossification
3. Development of Primary Ossification Center
(Occurs in the center of the diaphysis)
- Nutrient artery penetrates perichondrium and the calcifying cartilage; this stimulates osteogenic cells in the perichondrium to differentiate into osteoblasts (secrete bone tissue and matrix).
- The cells secrete beneath the perichondrium a thin shell of compact bone called the periosteal bone collar.
- Blood vessels and osteoblasts from periosteum and invade the disintegrating cartilage, and spongy bone forms in its place. (Medullary cavites formed, fill with bone marrow).

23. Endochondral Ossification
Development of Secondary Ossification Center (Occurs in the epiphyses of bone)
- Usually happens around time of birth
- This center appears in the epiphyses and spongy bone forms in all directions from them.
- As spongy bone is deposited in the diaphysis and epiphysis, a band of cartilage called the epiphyseal disk remains between the two ossification centers.

24. Endochondral Ossification
5. Formation of Articular Cartilage and Ephiphyseal Plate
- Hyaline cartilage that covers the epiphyses becomes the articular cartilage.
- Hyaline cartilage remains between the diaphysis and epiphysis is called the Epiphyseal Plate, which is responsible for the lengthwise growth of bones.

25. Endochondral Ossification

26. Bone Growth

27. Interstitial Growth Growth in Length
Grows from epiphyseal plate (growth plates)
When the epiphyseal plate closes and is replaced by bone, bone growth stops.

28. Appositional Growth Growth in Thickness
1. Bone grows in diameter as a result of addition of new bone tissue by osteoblasts around outer surface of the bone.

29. Bones and Homeostasis

30. Bone Remodeling Ongoing replacement of old bone tissue
Old bone is constantly destroyed by osteoclasts
New bone formed by osteoblasts

31. Fracture and Repair of Bone
Common Fractures:
a. Compound = open, protrude through skin
b. Closed = does not break skin
c. Comminuted = bone splinters; fragments
d. Greenstick = one side of bone breaks, while other side bends
e. Impacted = end of bone is driven into interior of another bone

33. Fracture Hematoma Blood leaks from torn vessels and a clot forms
Bone cells around fracture die and removed by osteoclasts
Stage lasts several weeks

34. Fibrocartilage Callus Formation
Granulation tissue (Procallus) is formed
Fibroblasts secrete collagen fibers to connect broken bones
Procallus is then transformed into a Fibrocartilaginous callus that connects the broken bones

35. Bony Callus Formation
Osteoblasts produce spongy bone which join the living and dead portions together
Fibrocartilage is converted into spongy bone

36. Bone Remodeling Compact bone replaces spongy bone around the fracture
Dead portions of original fragments are resorbed by osteoclasts

37. Bone Disorders Osteoporosis Rickets
Bone resorption outpaces bone formation
Hormonal change
Rickets
Disorder in which bones fail to calcify