Chapter 5 Bone Formation and Remodeling Pages 141-145

Ossification Animation This animation shows the development of the skeleton from conception through adulthood http://www.pennmedicine.org/encyclopedia/ em_DisplayAnimation.aspx?gcid=000112&pti d=17

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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

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) © 2015 Pearson Education, Inc.

Bone Remodeling Bones are lengthened until growth stops Bones are remodeled throughout life (every 7-10 years) in response to two factors: Blood calcium levels Pull of gravity and muscles on the skeleton © 2015 Pearson Education, Inc.

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) © 2015 Pearson Education, Inc.

Bone Growth Animation Showing appositional growth http://highered.mheducation.com/sites/007 2495855/student_view0/chapter6/animation __bone_growth_in_width.html

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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

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

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) © 2015 Pearson Education, Inc.

Table 5.2 Common Types of Fractures.