1. Skeletal System

2. I. Introduction A. Framework of bones & cartilage
B. Composed of various tissues
1. Bone
2. Cartilage
3. Epithelium
4. Fat
5. Neurons

3. C. Functions 1. Support 2. Protection 3. Movement 4. Mineral storage
5. Blood cell production
6. Fat storage

4. II. Bone Tissue A. Introduction 1. A kind of connective tissue
2. Crystals of inorganic calcium salts make it more rigid than other connective tissues
3. Network of collagen fibers provides flexibility & strength

5. B. Compact or dense bone tissue
1. Contains few spaces
2. Forms a layer over spongy bone
3. Provides protection, support & strength
4. Has a concentric ring structure

6. C. Spongy or cancellous bone tissue
1. Contains many large spaces
2. Makes up most of the bone tissue of:
i. Skull bones and vertebrae
ii. Epiphyses or tips of long bones

7. 3. Latticeworks of thin bone plates are called trabeculae
4. In some bones the spaces are filled with red marrow which produces blood cells
5. Spongy bone provides the greatest strength with the least weight

8. III. Bone Anatomy Parts of a typical long bone: A. Diaphysis
B. Epiphyses
C. Metaphysis
1. Where the diaphysis joins the epiphysis
2. Contains the epiphyseal plate were bone growth occurs

9. D. Medullary or marrow cavity
1. Space within the diaphysis
2. Contains fatty yellow marrow in adults
E. Endosteum
Layer of osteoblasts lining the marrow cavity & scattered osteoclasts
F. Articular cartilage
Thin layer of cartilage covering the epiphysis at a joint with another bone

10. G. Periosteum
1. Fibrous covering around the bone (where it is not covered by articular cartilage)
2. Consists of:
i. Connective tissue containing blood vessels
ii. Lymphatic vessels
iii. Nerves
iv. Cells that can become osteoblasts

12. IV. Microscopic Anatomy
A. Osteon or Haversian system
1. Structural unit of bone
2. Elongated cylinder parallel to bone’s long axis
3. Function as weight bearing pillars
4. Osteon is a hollow tube of bone
i. Like rings on a tree
ii. Each ring is called a lamella
5. Collagen fibers in adjacent lamella run in opposite directions

13. B. Central or Haversian canal
1. Canal that runs through the center of the osteon
2. Contains small blood vessels
3. Nerve fibers

14. C. Perforating or Volmann's canals
1. Lie at right angles to the central canal
2. Connect nerves & blood vessels in central canals with rest of the body

15. D. Osteocytes
1. Mature bone cells
2. Found in lacunae at the junctions of the lamellae
3. Canaliculi connect lacunae

16. E. Circumferential lamellae
1. Located on the outside or surface of the shaft
2. Surround the osteons inside the bone
3. Like bark on a tree

18. V. Bone formation & growth
A. Ossification – bone formation
1. Embryo begins with a 'skeleton' of cartilage & fibrous membranes shaped like bones
2. Ossification begins week after conception & continues throughout adulthood

19. 4. Once a framework is made, calcification occurs
3. Embryonic connective tissue cells multiply & enlarge & form cartilage & bone
4. Once a framework is made, calcification occurs
Calcium is deposited making the bone hard

20. 6. Bones also increase in diameter during growth
5. In long bones:
i. Shaft ossifies first
ii. Epiphyses ossify secondarily
iii. Epiphyseal plate between the shaft & ends remains cartilage
Permits growth of the bone shaft
iv. When lengthening stops the epiphyseal plate becomes the epiphyseal line
6. Bones also increase in diameter during growth

21. Allows bones & blood to exchange calcium
B. Bones are continuously remodeled
1. Bone tissue is reabsorbed & replaced
Allows bones & blood to exchange calcium
2. Controlled by remodeling units
i. Osteoblasts
ii. Osteoclasts
3. Diet must contain enough:
i. Calcium
ii. Phosphorus
iii. Vitamin D

22. C. Bone regulation hormones
1. Growth hormone
i Pituitary gland in the brain
ii. Regulates general body growth

23. 2. Calcitonin
i. Thyroid gland in the throat
ii. Promotes calcium deposition into bones
iii. Osteoblasts
3. Parathyroid hormone
i. Parathyroid glands in the throat
ii. Promotes removal of calcium from the bones
iii. Osteoclasts

24. 4. Serotonin
i. Made in the intestine
ii. A neurotransmitter
iii. Inhibits osteoblast production
iv. Shifts balance to the osteoclasts
v. Bone degradation

25. D. Hormonal control of remodeling
1. When blood concentration of Ca2+ is too high
i. Rising blood levels of stimulate calcitonin release
ii. Calcitonin stimulates the osteoblasts to deposit Ca2+ into bones
iii. Ca2+ concentration of blood returns to the homeostatic level

26. 2. When blood concentration of Ca2+ is too low
i. Falling Ca2+ levels stimulate parathyroid hormone release
ii. Hormone stimulates osteoclasts to degrade the bone
iii. Ca 2+ released into the blood
iv. Ca2+ levels in blood increase to the homeostatic level

27. E. Remodeling & mechanical factors
1. Functions to strengthen parts of the skeleton that are under stress
2. How this occurs is still uncertain
But may involve locally produced growth factors that stimulate the osteoblasts

28. 3. Aging shifts the balance between organic matter & calcium in bones
4. More inorganic salts & less organic matter
5. Causes less flexible & more brittle bones

29. VI. What looking at bones can tell you
A. Sex
1. Female pelvic opening
i. Wide & oval-shaped
ii. Wide to permit the passage of babies head

30. 2. Males
i. Narrow pelvic opening & heart-shaped
ii. Thicker skulls
iii. More prominent browridge

31. B. Age
1. Different bones have specific times that they stop growing
2. Teeth erupt at specific ages
3. Tooth wear

32. C. Other kinds of information
1. Based on minerals incorporated into bones:
i Diet
ii. Location person grew up based on the proportions of isotopes in the bones
2. Shapes & sizes of bones
i. Size of muscles
ii. Activities of a person