skeletal system axial vs. appendicular number of bones functions 1. support 2. mineral and lipid...
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• Skeletal System• Axial vs. Appendicular
• Number of Bones
• Functions• 1. Support
• 2. Mineral and Lipid storage
• 3. Hematopoiesis
• 4. Protection
• 5. Leverage
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• Bone Shapes• 1. Long
• 2. Short
• 3. Flat
• 4. Irregular
• 5. Sutural
• 6. Sesamoid
• Structural Types • 1. Compact • 2. Spongy
IntroductionIntroduction
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• Structure of a Long Bone• Diaphysis – ”shaft”
• medullary cavity
• Epiphyses • distal and proximal
• Metaphyses
• Cartilage• Articulating surface
• Hyaline cartilage
• Periosteium • Covers compact bone
• Endosteum • Medullary cavity membrane
Structural Characteristics of BoneStructural Characteristics of Bone
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• Osteons – Haversian Units • Central (Haversian canal)
• Lamellae
• Osteocytes in ‘lacunae’
• Perforating Canals
• Periosteal arteries
• Canaliculi
• Other Cell Types • Osteogenic
• Osteoblasts
• Osteoclast cells
Histology of Compact Bone Tissue Histology of Compact Bone Tissue
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• Calcium salts interact to form hydroxyapaptite crystals
• Calcium phosphate + calcium hydroxide
• Calcium carbonate is added along with ions (sodium, magnesium, etc.)
• Collagen fibers give bone flexibility
Matrix of BoneMatrix of Bone
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• 1. Do not contain osteons.
• 2. Lamellae – irregular arrangement• Trabeculae
• 3. Light
• 4. Support and protects red bone marrow
• Location • Short, flat and irregular bone
• Location of Red Marrow• Hips, ribs, breastbone, vertebrae, epiphysis of long bones
How Does Spongy Bone Histology differ from Compact Bone?How Does Spongy Bone Histology differ from Compact Bone?
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• Bones begin their formation during embryonic development
• Ossification vs. calcification
• Two methods of bone formation: • 1. Intramembranous Ossification
• 2. Endochondral Ossification
How do Bones Form?How do Bones Form?
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• Osteoblasts differentiate in mesenchymal fibrous connective tissue • ‘Dermal ossification’
• Dermal bones formed
• Examples: flat bones of skull; mandible; clavicle
Intramembranous Ossification Intramembranous Ossification
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• A cartilage model is replaced by bone.
• Six-Eight weeks bones are made of cartilage
• Cartilage continues to expand (interstitial growth) and new cartilage develops at outer surface (appositional growth)
• Role of osteoclast cells
• Ossification centers
Endochondrial OssificationEndochondrial Ossification
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Endochondrial Ossification Endochondrial Ossification
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• Gigantism• GH overproduced in puberity
• Acromegaly
• Post-puberity (bones thicken)
• Dwarfism • Pituitary growth failure
Abnormal Bone Growth Abnormal Bone Growth
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• Diet• Calcium and phosphate
• Homones• Calcitriol - from vitamin D
• Growth Hormone
• Estrogen – females
• Androgens – males
• Vitamins• D, A, K and B12
What is needed to allow for normal bone growth and repair? What is needed to allow for normal bone growth and repair?
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• Two hormones must be balanced: • Parathyroid hormone (PTH)• Calcitonin
• Homeostatic Control• Effects of PTH – counteracts low calcium levels
• Stimulates osteoclast activity
• Increases intestinal absorption of calcium ions
• Decreases rate of calcium
• Effects of calcitonin – counteracts high calcium levels • Inhibits osteoclast activity
• Increases rate of excretion of calcium ions
• Calcium Reserves
Homeostatic Control Homeostatic Control
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Calcium Homeostasis Calcium Homeostasis
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• Osteopenia is a natural process
• Reduction in bone mass – osteoporosis
• Risk Factors • Sex-hormones• Smoking • Other
Consequences of Calcium Imbalances Consequences of Calcium Imbalances
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• Fractures • Compound vs. Simple
• Stress Fractures
• Repair• Blood clot (hematoma) forms
• Internal and external callus eventually replaced by bone.
• Remodeling • Bone constantly removed and replaced
• Young: 1/5th replaced every year
• Spongy bone replaced faster, more often
Bad Breaks, Repair and Remodeling Bad Breaks, Repair and Remodeling