2011 Calcium Metabolsim and Control of Growth

2011 Calcium Metabolsim and Control of Growth - Dr. Kennon...

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E-76 Dr. Kennon M. Garrett CALCIUM HOMEOSTASIS AND CONTROL OF GROWTH Reading: Vander et al., Human Physiology, 12 th ed. pp. 340-349. Behavioral Objectives 1. List the functions of osteoclasts and osteoblasts in bone resorption and bone formation 2. List the hormones responsible for Ca regulation. 3. Describe the synthesis of 1,25-dihydroxy vitamin D3 4. Describe the mechanisms by which parathyroid hormone regulates Ca homeostasis. 5. List factors that affects growth. 6. List effects and mechanisms of growth hormone on growth. 7. Describe the regulation of growth hormone release. 8. List effects of IGF-1 on growth. 9. List other hormones that affect growth and know what effects they have on growth. I. Calcium Regulation A. Organs involved in Ca 2+ regulation 1. GI tract Ca 2+ is absorbed from the small intestine. Approximately 1 gm of Ca 2+ is ingested each day and the GI tract absorbs about 1/3 of the ingested Ca 2+ . The absorption of Ca 2+ is regulated by 1,25- dihydroxyvitamin D 3 . 2. Kidneys The kidneys reabsorb 99% of the filtered Ca 2+ . 90% is reabsorbed in the proximal tubule and loop of Henle. 9% is reabsorbed in the distal segment and is regulated by parathyroid hormone. The kidneys play an indirect role in Ca 2+ regulation though the synthesis of 1,25- dihydroxyvitamin D 3 3. Bone - the major storage site for Ca 2+ and phosphate
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E-77 B. Hormones involved in Ca 2+ regulation 1. Parathyroid hormone (PTH) - primary hormone responsible for Ca 2+ homeostasis 2. 1,25-dihydroxyvitamin D 3 (1,25-dihydroxycholecalciferol, calcitrol) 3. Calcitonin C. Sources of body Ca 2+ Total body calcium - 1 - 2 kg Bone - 99% of total Ca 2+ Extracellular - 0.1%, In plasma, 50% of Ca 2+ is bound to serum proteins and inorganic anions Intraceullular - 0.9% II. Bone structure A. Compact bone (aka cortical bone) 80% of bone mass B. Spongy bone (aka trabecular bone) 20% of total bone mass C. Extracellular bone composition 1. osteoid - organic matrix made up of collagen and other proteins 2. hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 )- crystals that form the mineral matter of bone. The hydroxyapatite crystals precipitate on the osteoid. D. Bone Cells (Fig 11-29) 1. osteoclasts - cells that resorb bone 2. osteoblasts - cells that form bone 3. osteocytes - cells in the interior of bone
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E-78 III. Bone remodeling Osteoclasts are located on the surface of bone. They secrete acid and enzymes that dissolve bone and release Ca 2+ and phoosphate into the extracellular fluid. This Ca 2+ and phhosphate can be picked up by the blood vessels or taken up by neighboring osteoblasts. Osteoblasts are adjacent to the osteocytes. These cells synthesize and secrete osteoid into the extracellular matrix. They also secrete Ca 2+ and phosphate to form hydroxyapatite crystals on the osteoid. As the bone is formed around the osteoblats, they are trapped in the bone matrix and become osteocytes. The balance between the bone reabsorption by the osteoclasts and the bone formation by the osteoblasts
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2011 Calcium Metabolsim and Control of Growth - Dr. Kennon...

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