1. Learning Plan 4--Ch. 6 Bones and Skeletal Tissue
Pages , Michael Aprill Lakeshore Technical College

2. Skeletal system is composed of bone & cartilage.
Bones of the Skeleton
Each bone is an organ.
Skeletal system is composed of bone & cartilage.
Two main groups of bone, by location
Axial skeleton
Appendicular skeleton

3. Classification of Bones by Shape (Fig. 6.2)
Long bones
Longer than they are wide
Short bones
Cube-shaped bones (in wrist and ankle)
Sesamoid bones (within tendons, e.g., patella)
Flat bones
Thin, flat, slightly curved
Irregular bones
Complicated shapes

4. Figure 6.2

5. Functions of Bones Support Protection Movement Storage
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

6. Blood cell formation (hematopoiesis) in marrow cavities
Functions of Bones
Blood cell formation (hematopoiesis) in marrow cavities
Adults: red marrow cavities of femur, head of humerus, & flat bones
Newborn: medullary cavities & spongy bone.
Triglyceride (energy) storage in bone cavities

7. Bone Markings: Projections (See Table 6.1)
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

8. Table 6.1

9. Bone Markings: Projections (See Table 6.1)
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

10. Table 6.1

11. Bone Markings: Depressions and Openings (See Table 6.1)
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

12. Table 6.1

13. Bone Textures (See Fig. 6.5)
Compact bone
Dense outer layer
Spongy (cancellous) bone
Honeycomb of trabeculae

14. Structure of a Long Bone (Fig. 6.3A-B)
Diaphysis (shaft)
Compact bone collar surrounds medullary (marrow) cavity
Medullary cavity in adults contains fat (yellow marrow)

15. Structure of a Long Bone (See Figure 6.3A-B)
Epiphyses
Expanded ends
Spongy bone interior
Epiphyseal line (remnant of growth plate)
Articular (hyaline) cartilage on joint surface
Functions to reduce friction between bones
Structure of a Long Bone (See Figure 6.3A-B)

16. Membranes of Bone Periosteum Outer fibrous layer
Inner osteogenic layer
Bone forming Cells (osteoblasts)—secrete bone matrix
Bone destroying cells (osteoclasts). Give rise to stem cells (osteogenic cells)

17. Membranes of Bone (Fig. 6.3C)
Endosteum
Delicate membrane on internal surfaces of bone
Also contains osteoblasts and osteoclasts

18. Microscopic Anatomy of Bone
(a) Osteogenic cell
(b) Osteoblast
Stem cell
Matrix-synthesizing
cell responsible
for bone growth
Figure 6.4a-b

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

20. Microscopic Anatomy of Bone: Compact Bone (See Fig. 6.6)
Haversian system, or osteon—structural unit
Lamellae
Weight-bearing
Column-like matrix tubes
Central (Haversian) canal
Contains blood vessels and nerves

21. Microscopic Anatomy of Bone: Compact Bone (See Fig. 6.7A-C)
Lacunae—small cavities that contain osteocytes
Canaliculi—hairlike canals that connect lacunae to each other and the central canal

22. Microscopic Anatomy of Bone: Spongy Bone
Trabeculae
Align along lines of stress
No osteons
Irregularly arranged lamellae, osteocytes, and canaliculi

23. 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

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

25. 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

26. Two Types of Ossification (osteogenesis) See Figure 6.8
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

27. Intramembranous Ossification (Fig. 6.8A-D)

28. Endochondral Ossification
Uses hyaline cartilage models
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. Postnatal Bone Growth Interstitial growth: Appositional growth:
 length of long bones
Only means by which diaphysis increases in length is epiphyseal (growth) plate
Epiphyseal plate closes & is replaced by bone.
Once epiphyseal line appears, it indicates interstitial growth has ended. Between ages
Appositional growth:
 thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces

32. Factors Affecting Bone Growth
Nutrition
Adequate minerals & vitamins
Calcium and phosphorus
Vitamin C
Vitamin K and B12
Sufficient levels of specific hormones
Insuline Like Growth Factors (IGFs)—needed during childhood.
Stimulated by hGH
Thyroid hormones & insulin
Sex steroids (estrogen & testosterone) at puberty stimulate sudden growth & modifications of skeleton to produce male/female forms.

33. Bone Deposit 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
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

34. 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

35. 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 and gravitational forces

36. Classification of Bone Fractures (See Table 6.2)
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

37. Classification of Bone Fractures
Orientation of the break to the 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

38. Table 6.2

39. Table 6.2

40. Table 6.2

41. Stages in the Healing of a Bone Fracture
Hematoma forms (after 6-8 hours)
Torn blood vessels hemorrhage
Clot (hematoma) forms
Site becomes swollen, painful, and inflamed

42. 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

43. 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

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

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

46. Homeostatic Imbalances
Osteoporosis
Loss of bone mass—bone resorption outpaces deposit
Spongy bone of spine and neck of femur become most susceptible to fracture
Risk factors
Lack of estrogen, calcium or vitamin D; petite body form; immobility; low levels of TSH; diabetes mellitus

47. 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

48. Developmental Aspects of Bones
Nearly all bones completely ossified by age 25
Bone mass decreases with age beginning in 4th decade
Decreased rate of protein synthesis:
Decreased collagen
Decreased bone growth hormone
Becomes brittle/susceptible to fracture