Ch. 11 Calcium Homeostasis

Osteoclasts reabsorb break down old bone and then

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Osteoclasts reabsorb, break down old bone and then osteoblasts (bone forming cells) move into the area and lay down new matrix, which becomes mineralized. The process occurs and depends on the stresses that gravity and muscle tension impose on the bones, stimulating osteoblastic activity. Factors influencing bone remodeling: the following hormones favor bone formation and increased bone mass: insulin, GH, IGF-1, estrogen, testosterone & calcitonin. The following hormones favor increased bone reabsorption and decreased bone mass: parathyroid hormone, cortisol, T3 & T4. 3. How is parathyroid hormone secretion regulated? What are the major actions of parathyroid hormone? (Sect11F.1, Fig11.31)
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Biol 2173 Learning Objectives Spring 2013 Diagram p. 347 Parathyroid hormone production is controlled by the extracellular Ca 2+ concentration acting directly on secretory cells via plasma membrane Ca 2+ receptors. DECREASED plasma Ca 2+ concentration stimulates parathyroid hormone secretion, and increased plasma Ca 2+ concentration does the opposite. Major actions of PTH- overall increases calcium concentration; directly increases resorption of bone by osteoclasts, which causes calcium and phosphate ions to move from
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