anim_bone_growth_remodeling_answer_key.doc

Bone Growth & Remodeling To complete this worksheet, select: Module: Support and Movement Activity: Animations Title: Bone Growth & Remodeling Complete the following worksheet and add it to your notes. Contrast the effects of appositional and interstitial growth. Which occurs at the periosteum? Postpartum, bones develop in thickness through appositional buildup at the periosteum. In contrast, interstitial growth allows for the lengthwise development of long bones at the epiphyseal plates located at the end of the bones (epiphysis.) What is bone remodeling, and why does it occur? Bone remodeling is the action of reshaping and resizing bone tissue to adapt to changing physical requirements. Bone growth occurs from infancy until the mid-20’s. However, bone remodeling never ceases and persists throughout an individual’s lifespan. Intramembranous Ossification How does bone shaft thickness and width remain proportional during bone remodeling? a. Osteoclast activity It is through the action of osteoclasts, as well as appositional growth that the bone dimensions are proportionally maintained while it is remodeled. b. Appositional growth (periosteum and endosteum) This is the other factor that controls the bone’s symmetry (ie. thickness and articulations) while it is reshaped. All bones undergo widening, but only some undergo interstitial lengthening. Which bones undergo interstitial lengthening? Only the bones located in the appendages experience interstitial lengthening. a. Where does bone lengthening occur? This specifically transpires at the epiphyseal plates. Describe the four zones of the epiphyseal plate, and the function of each: a. Zone of Resting Cartilage this is a region of hyaline cartilage made of dormant chondrocytes. This region secures the plate to the epiphysis. b. Zone of Proliferating Cartilage this is the mitotic layer of chondrocytes that drives the resting layer outward. This action results in elongation the diaphysis. c. Zone of Hypertrophic Cartilage this is site where chondrocytes build up and enlarge, which in turn expands the lacunae. Its overall effect adds to the lengthening of the shaft. d. Zone of Calcified Cartilage this is a thin area (a few cells thick) containing expiring and deceased chondrocytes. This layer grounds the epiphyseal plate to the diaphysis. Describe the role of the osteoclasts and osteoblasts. Osteoclasts act to decompose the calcified cartilage. Osteoblasts, in turn, replace the calcified cartilage with bone extracellular matrix What forms the epiphyseal line? This happens when an individual reaches their adult stature. Once bone growth ceases, the epiphyseal plate’s cartilage is replace by bone and the epiphyseal line is left as a reminant of the epiphyseal plate. What is the role of the periosteum? This membrane found to cover the surface of bone. It is composed of connective tissue, osteogenic cells, and osteoblasts. It is critical for bone growth, repair, & nourishment. It is also offers an attachment site for tendons and ligaments. Describe the role of the following with regard to bone widening. a. Osteogenic cells These progenitor cells give rise to osteoblasts that participates in bone formation. b. Osteoblasts These cells produce bony matrix that is composed of organic compounds & inorganic salts. c. Groove formation This is the bony area produced by osteoblasts that is found around a periosteal blood vessel. d. Central canal The ridges of the groove formation merge forming this central canal structure. This encompasses the periosteal blood vessel. e. Endosteum This is the lining that develops around the blood vessel within the central canal. It also contains osteogenic cells. f. Lamellae formation Osteoblasts continue to add bony matrix that form these circular structures called lamellae. g. New Osteon formation This is accomplished as osteoblasts continue creating lamellae inwardly to the periosteal blood vessel which lead to the creation of a new structural unit of bone. Describe the role of osteoclasts along the inner surface of bone at the endosteum. While the bone boundary expands outward on the periphery at the periosteum, osteoclasts found on the endosteum break down the inner surface of bone. This leads to a bone with a larger breadth & bigger medullary cavity.