Transcript No Slide Title
Mineral Deposition
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Mineralization is crystallization process
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osteoblasts produce collagen fibers spiraled the length of the osteon
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minerals cover the fibers and harden the matrix
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ions (calcium and phosphate and from blood plasma) are deposited along the fibers
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ion concentration must reach the solubility product for crystal formation to occur Abnormal calcification (ectopic)
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may occur in lungs, brain, eyes, muscles, tendons or arteries (arteriosclerosis) 7-1
Mineral Resorption from Bone
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Bone dissolved and minerals released into blood
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performed by osteoclasts
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hydrochloric acid (pH 4) dissolves bone minerals enzyme (acid phosphatase) digests the collagen Dental braces reposition teeth and remodel bone
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create more pressure on one side of the tooth
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stimulates osteoclasts to remove bone decreased pressure stimulates osteoblasts 7-2
Calcium and Phosphate
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Phosphate is component of DNA, RNA, ATP, phospholipids, and pH buffers
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Calcium needed in neurons, muscle contraction, blood clotting and exocytosis 7-3
Ion Imbalances
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Changes in phosphate levels = little effect Changes in calcium can be serious
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hypocalcemia is deficiency of blood calcium
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causes excitability of nervous system if too low
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muscle spasms, tremors or tetany ~6 mg/dL
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laryngospasm and suffocation ~4 mg/dL
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with less calcium, sodium channels open more easily, sodium enters cell and excites neuron
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hypercalcemia is excess of blood calcium
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binding to cell surface makes sodium channels less likely to open, depressing nervous system
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muscle weakness and sluggish reflexes, cardiac arrest ~12 mg/dL Calcium phosphate homeostasis depends on calcitriol, calcitonin and PTH regulation 7-4
Carpopedal Spasm
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Hypocalcemia demonstrated by muscle spasm of hands and feet.
7-5
Hormonal Control of Calcium Balance
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Calcitriol, PTH and calcitonin maintain normal blood calcium concentration.
7-6
• • •
Calcitriol (Activated Vitamin D)
Produced by the following process
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UV radiation and epidermal keratinocytes convert precursor to vitamin D3
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liver converts it to calcidiol kidney converts that to calcitriol (vitamin D) Calcitriol behaves as a hormone that raises blood calcium concentration
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increases intestinal absorption and absorption from the skeleton
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increases stem cell differentiation into osteoclasts
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promotes urinary reabsorption of calcium ions Abnormal softness (rickets) in children and (osteomalacia) in adults without vitamin D 7-7
Calcitriol Synthesis and Action
7-8
Calcitonin
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Secreted (C cells of thyroid gland) when calcium concentration rises too high Functions
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reduces osteoclast activity as much as 70% increases the number and activity of osteoblasts Reduces bone loss in osteoporosis 7-9
Correction for Hypercalcemia
7-10
Parathyroid Hormone
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Glands on posterior surface of thyroid Released with low calcium blood levels Function = raise calcium blood level
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causes osteoblasts to release osteoclast-stimulating factor increasing osteoclast population
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promotes calcium resorption by the kidneys promotes calcitriol synthesis in the kidneys inhibits collagen synthesis and bone deposition by osteoblasts 7-11
Correction for Hypocalcemia
7-12
Other Factors Affecting Bone
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Hormones, vitamins and growth factors Growth rapid at puberty
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hormones stimulate osteogenic cells, chondrocytes and matrix deposition in growth plate
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girls grow faster than boys and reach full height earlier (estrogen stronger effect)
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males grow for a longer time and taller Growth stops (epiphyseal plate “closes”)
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teenage use of anabolic steroids = premature closure of growth plate and short adult stature 7-13