1. Textbook Reference: chapter 5
Skeletal System
Textbook Reference: chapter 5

2. Unit ___ Goals
Differentiate between the axial and appendicular skeletons
Define the 5 functions of bone
Differentiate between the 2 types of boney tissue and the 4 classes of bone in the body
Identify the microscopic components to bone
Differentiate between the 3 types of bone cells
Describe the different modes of bone growth and the reasons for such growth
Define the need for spinal curvatures and the dangers of excessive curves
Define the function of intervertebral discs
Describe the reasons for gender differences of bones
Identify the major bones of the body and the class to which they belong

3. The Skeletal System
Your skeleton comprises ~ 20% of your total body mass
There are 206 bones in your body, separated into 2 divisions:
1. Axial skeleton: head, vertebrae and rib cage
2. Appendicular Skeleton: pelvis, scapulae and limbs

4. Axial: pink Appendicular: green

5. 5 Functions of Bones
Support: legs support the weight of body, ribs support thoracic cavity
Protections: protects all soft tissue organs
Movement: muscles use bones as levers, allowing for movement
Storage: fat stored in internal cavities of bones; calcium and phosphorus also stored
Blood Cell Formation: hematopoesis; the production of blood cells within marrow cavities

6. Bone Types There are two types of bones:
1. Compact bone: dense bone which is smooth and solid; surrounds all bone; appears dense
2. Spongy bone: internal portion of bone; consists of small needle-like projections of bone called trabeculae with many open spaces filled with marrow

7. Bone Types

8. Bone Classification
Bones come in many shapes and sizes and are classified into 4 distinct groups:
Long Bones
Longer than wide
Built to absorb stress
Consists of a shaft and 2 heads at each end
Mostly compact but some spongy bone internally
Examples: all bones of limbs except patella, carpals and tarsals

9. Long Bone: the femur

10. Bone Classification 2. Short Bones Roughly cube-like
Contains mostly spongy bone
Thin layer of compact bone on surface
Examples: carpals and tarsals
Sesamoid bone: a bone embedded in a tendon; varies in size and numbers/each individual; act to alter the pull of a tendon; i.e. patella

11. Short Bones: carpals of the wrist

12. Bone Classification 3. Flat Bones Thin, flattened and usually curved
2 parallel compact surfaces with a spongy layer between
examples: sternum, ribs and skull bones

13. Bone Classification 4. Irregular Bones
Do not fit any other classification
Complicated shapes
Mostly spongy with thin compact layer
Examples: vertebrae and hip bones

14. Anatomical Structure of a Long Bone
Diaphysis: shaft of long bone; walls made of compact bone
Periosteum: fibrous sheath that covers long bones
Highly vascularized
Functions in bone nourishment and attachment sites

15. Anatomical Structure of a Long Bone
Sharpey’s Fibers: connective tissue fibers that secures the periosteum to underlying bone
Epiphyses: ends of long bones
Enlarged for muscle attachment
Predominately spongy bone

16. Anatomical Structure of a Long Bone
Articular Cartilage: covers ends of epiphyses and provides a slippery surface that decrease friction at joint surfaces
Medullary Cavity: holds marrow in center of diaphysis
Yellow marrow: fat storage in adults, found in medullary cavity
Red marrow: found in diaphysis of infants, in flat bones & epiphyses of adults; makes red blood cells

17. Anatomical Structure of a Long Bone
Endosteum: sheath covering medullary cavity

18. Bone Composition Bone contains inorganic & organic components
Inorganic calcium carbonate & calcium phosphate; provides hardness
Organic collagen: to further reinforce the matrix

19. Osteoporosis: brittle bones
Normal Spongy Bone
Osteoporotic Spongy Bone

20. Bone Cells: 3 Types
Osteoblasts: arise from embryonic cells and found on outer surfaces of adult bones; aid in matrix production
Osteocytes: mature bone cells; trapped in lacunae
Osteoclasts: secretes substances that dissolve mineral salt crystals

21. Bone – cell types Note locations of Osteoclasts & osteoblasts
“Ruffled” Border

22. Microscopic Anatomy of Bone
Lacunae: cavities in bones where osteocytes are found
Lamellae: a circular layer of bone

23. Microscopic Anatomy of Bone
Haversion Canals: a system of interconnecting canals in adults compact one; runs lengthwise through bone, carrying blood vessels and nerves to all areas of bones
Canaliculi: tiny canals that connect all the bone cells to the nutrient supply; radiate outward from Haversion Canals

24. Microscopic Anatomy of Bone
Volkmann’s Canals: communication system from exterior of bone to interior; runs at right angle to diaphysis
Osteon/Haversion Systems: each haversian canal with lamellae, osteocytes and caniliculi

25. Haversion Systems

26. Bone Development Embryonic Skeleton: predominately hyaline cartilage

27. Bone Development
Young child to late adolescence: cartilage replaced by bone
Epiphyseal Growth Plates: allows for interstitial growth (lengthwise)
Cartilage near the epiphyses regenerates
Cartilage near the diaphysis hardens to bone eventually they’ll meet, halting lengthwise growth
Fontanels: in skull at birth; allows for growth of brain

28. Epiphyseal Growth Plate

29. Epiphyseal Growth Plates
Growing
Adult

30. Bone Development & Growth

31. Ossification The replacement of cartilage by bone
Cartilage is covered by osteoblasts
Cartilage is “eaten” away, leaving the medullary cavity open within the bone

33. Appositional Growth Outward growth of bone during adulthood
Bones change based on calcium levels & muscles acting on the skeleton
Decreased blood calcium leads to bone breakdown
Increased demand by muscles on bones causes bone to thicken
Weight gain also increase bone diameter
Adult bone constantly remodels (breakdown & growth) to help maintain homeostasis of blood mineral levels