1. Chapter 5 Bone Formation and Remodeling
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2. Ossification Animation This animation shows the development of the skeleton from conception through adulthood
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3. Ossification (Bone Formation) and Growth
There are two major phases of ossification in long bones
Osteoblasts (builder cells)
osteoblasts multiply (through mitosis)
cartilage calcifies- it is replaced with bone by the osteoblasts
Cartilage inside the diaphysis is digested away
This opens up the medullary cavity
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4. Bone Formation and Growth
By birth, most cartilage is converted to bone except:
Articular cartilages (the epiphyseal surfaces)
Epiphyseal plates
New cartilage is continuously formed by chondrocytes
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5. Bone Formation and Growth
Bones grow in two ways:
length (longitudinal)
width (appositional)
Growth in diameter
Controlled by growth hormones
Epiphyseal plates are converted from cartilage to bone during adolescence
Fused by the age of 18 (W), 21 (M)
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6. Bone Remodeling Bones are lengthened until growth stops
Bones are remodeled throughout life (every years) in response to two factors:
Blood calcium levels
Pull of gravity and muscles on the skeleton
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7. Bone Remodeling Parathyroid hormone (PTH)
Released when blood calcium levels are low
Activates osteoclasts (bone-destroying cells)
Osteoclasts break down bone and release calcium ions into the blood
Hypercalcemia (high blood calcium levels) prompts calcium storage to bones
Regulated by calcitonin (secreted by thyroid)
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8. Bone Growth Animation Showing appositional growth
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9. Bone Fractures- a break in a bone
Bone fractures are treated by reduction and immobilization
Closed reduction: bones are manually coaxed into position by physician’s hands
Open reduction: bones are secured with pins, screws, or wires during surgery
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10. Steps of Fracture Repair
Hematoma (blood-filled swelling) is formed
Fibrocartilage callus forms
A soft mixture of cartilage matrix, bony matrix, and collagen fibers splint the broken bone
Bony callus (hard) replaces the fibrocartilage callus
Osteoblasts and osteoclasts migrate in
Bone remodeling- compact bone replaces cartilage
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11. Figure 5.7 Stages in the healing of a bone fracture.
Hematoma
External callus
Bony callus of spongy bone
New blood vessels
Internal callus (fibrous tissue and cartilage)
Healed fracture
Spongy bone trabecula
Hematoma forms. 1
Fibrocartilage callus forms. 2
Bony callus forms. 3
Bone remodeling occurs. 4

12. Common Types of Fractures
Closed (simple) fracture: break that does not penetrate the skin
Open (compound) fracture: broken bone penetrates through the skin
Comminuted: bone breaks into many fragments
Compression: bone is crushed
Depressed: broken bone portion is pressed inward
Impacted: broken bone ends are forced into each other
Spiral: ragged break occurs when excessive twisting forces are applied to a bone
Greenstick: bone breaks incompletely (common in children)
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13. Table 5.2 Common Types of Fractures.