Chapter 5 Bone Formation and Remodeling Pages 141

Chapter 5 Bone Formation and Remodeling Pages 141 -145

Ossification (Bone Formation) and Growth 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 © 2015 Pearson Education, Inc.

Bone Formation and Growth By birth, most cartilage is converted to bone except: 1. Articular cartilages (the epiphyseal surfaces) 2. 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: 1. Blood calcium levels Negative feedback mechanisms to provide calcium to the nervous and muscular systems 2. Pull of gravity and muscles on the skeleton © 2015 Pearson Education, Inc.

Bone Remodeling Calcium Levels are LOW (hypocalcemia) ◦ Release of Parathyroid Hormone by the Parathyroid glands ◦ Activates osteoclasts (bone-destroying cells) Osteoclasts break down bone and release calcium ions into the blood stream Calcium Levels are HIGH (hypercalcemia) ◦ Release of Calcitonin Hormone by the Thyroid gland ◦ Activates osteoblasts (bone-building cells) Osteoblasts use calcium and phosphorus to build bone © 2015 Pearson Education, Inc.

Bone Growth Animation Showing appositional growth http: //highered. mheducation. com/sites/007 2495855/student_view 0/chapter 6/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 1. 2. 3. 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 Bony callus (hard) replaces the fibrocartilage callus 1. Osteoblasts and osteoclasts migrate in 4. Bone remodeling- compact bone replaces cartilage © 2015 Pearson Education, Inc.

Figure 5. 7 Stages in the healing of a bone fracture. Hematoma Bony callus of spongy bone External callus Internal callus (fibrous tissue and cartilage) 1 Hematoma forms. 2 Fibrocartilage callus forms. New blood vessels 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) © 2015 Pearson Education, Inc.

Table 5. 2 Common Types of Fractures.

Arm Bones

Hip and Thigh (Femur)

Hip and Thigh Bones

Anterior and Posterior View of Femur