Chapter 5 The Skeletal System 115 Copyright Goodheart-Willcox Co., Inc. Growth and Development of Bones Over the course of the life span from birth through old age, some parts of the body grow, while others tend to shrink. Knowledge of the processes by which bones grow and develop is the key to understanding why these phenomena occur. Osteoblasts and Osteoclasts Specialized bone cells called osteoblasts carry out the work of building new bone tissue. Other specialized cells called osteoclasts resorb, or eliminate, weakened or damaged bone tissue. nutrients and removal of waste products throughout the Haversian system. The multiple Haversian systems are joined by perforating (Volkmann’s) canals, also running sideways. SELF CHECK 1. What percentage of bone weight comes from its mineral content? 2. What is collagen? 3. Where is cortical bone typically found? 4. Where is trabecular bone typically found? 5. What is the purpose of a Haversian system? Periosteum Cortical bone Blood vessel Haversian canal Perforating (Volkmann’s) canal B Magnified view A Pie-shaped section Spongy bone Osteons (Haversian system) Blood vessel continues into medullary cavity containing marrow Lamellae Lamella Osteocyte Canaliculus Lacuna Haversian canal © Body Scientifi c International Figure 5.7 A—A microscopic view of the inside of bone tissue. B—An even more magnified view of the diaphysis. Understanding Medical Terminology Osteoblast and osteoclast are similar-sounding names for these specialized bone cells. An easy way to avoid confusing them is to remember the “b” in osteoblast is the same as the “b” in build. Similarly, the “cl” in osteoclast is the same as the “cl” in clear. Osteoblasts build bone and osteoclasts clear away old or damaged bone.