Transcript Chapter 5 Bone Formation and Remodeling

Pages 141-145
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There are two major phases of ossification in
long bones
1. Osteoblasts (builder cells)
 osteoblasts multiply (through mitosis)
 cartilage calcifies- it is replaced with bone by the
osteoblasts
2. Cartilage inside the diaphysis is digested away

This opens up the medullary cavity
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By birth, most cartilage is converted to bone
except:
1. Articular cartilages (the epiphyseal surfaces)
2. Epiphyseal plates
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New cartilage is continuously formed by
chondrocytes
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Bones grow in two ways:
◦ length (longitudinal)
◦ width (appositional)
 Growth in diameter
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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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Bones are lengthened until growth stops
Bones are remodeled throughout life (every
7-10 years) in response to two factors:
1. Blood calcium levels
2. Pull of gravity and muscles on the skeleton
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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
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Hypercalcemia (high blood calcium levels)
prompts calcium storage to bones
◦ Regulated by calcitonin (secreted by thyroid)
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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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1.
2.
Hematoma (blood-filled swelling) is formed
Fibrocartilage callus forms
1. A soft mixture of cartilage matrix, bony matrix, and
collagen fibers splint the broken bone
3.
Bony callus (hard) replaces the fibrocartilage
callus
1. Osteoblasts and osteoclasts migrate in
4.
Bone remodeling- compact bone replaces
cartilage
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Figure 5.7 Stages in the healing of a bone fracture.
Hematoma
External
callus
Internal
callus
(fibrous
tissue and
cartilage)
1 Hematoma
forms.
2 Fibrocartilage
callus forms.
New
blood
vessels
Bony
callus of
spongy
bone
Healed
fracture
Spongy
bone
trabecula
3 Bony callus
forms.
4 Bone
remodeling
occurs.
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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Table 5.2 Common Types of Fractures.