• Skeletal System• Axial vs. Appendicular

• Number of Bones

• Functions• 1. Support

• 2. Mineral and Lipid storage

• 3. Hematopoiesis

• 4. Protection

• 5. Leverage

• Bone Shapes• 1. Long

• 2. Short

• 3. Flat

• 4. Irregular

• 5. Sutural

• 6. Sesamoid

• Structural Types • 1. Compact • 2. Spongy

IntroductionIntroduction

• 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

• 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

• 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

• 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?

• 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?

• Osteoblasts differentiate in mesenchymal fibrous connective tissue • ‘Dermal ossification’

• Dermal bones formed

• Examples: flat bones of skull; mandible; clavicle

Intramembranous Ossification Intramembranous Ossification

• 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

Endochondrial Ossification Endochondrial Ossification

• Gigantism• GH overproduced in puberity

• Acromegaly

• Post-puberity (bones thicken)

• Dwarfism • Pituitary growth failure

Abnormal Bone Growth Abnormal Bone Growth

• 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?

• 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

Calcium Homeostasis Calcium Homeostasis

• Osteopenia is a natural process

• Reduction in bone mass – osteoporosis

• Risk Factors • Sex-hormones• Smoking • Other

Consequences of Calcium Imbalances Consequences of Calcium Imbalances

• 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