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Spinach has the worse calcium bioavailability
Same reason as with Iron, due to oxalate that bind to the free Ca and Fe and won't release it
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What inhibits Ca bioavailability?
- Phytates (beans)
- Polyphenols (tea/coffee)
- Oxalate (Spinach)
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When is absorption of Ca increased? (4)
- 1) low Ca diet
- 2) Pregnancy
- 3) Lactation
- 4) growth
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Ca utilizes what kind of absorption?
Paracellular
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What type of pH is needed to absorb Ca?
Low pH
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If the pH is high, what will bind and sequester Ca?
Phosphate to form insoluble calcium phosphate
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When Ca is low, what absorption path is used?
Transcellular
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Are Paracellular and Transcellular absorption Vit. D dependent/Ind.?
- Paracellular: independent
- Transcellular: dependent
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What form of Vit. D is necessary for transcellular absorption?
Calcitriol 1,25 (OH)2D3
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Where are TRPV5/6 located and what is their function?
- TRPV5 = kidney
- TRPV6 = liver
- **both absorb Ca for transcellular absorption
- **transcribed by calcitriol in the nucleus
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What binds Ca to keep it unbound from Phosphate?
Calbindin
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What are the two basolateral transporters of Ca?
- Ca-ATPase - primary active transport
- NA/CX - Secondary active transport
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How is Vit. D3 formed and what is it called?
7-dehydrocholesterol + UV light = Cholecalciferol (Vit. D3)
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What contains vit. D2 and what is it called?
- Found in plants/plankton
- Ergocalciferol
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What are the three forms of vitamin D called?
- Vitamin D: Calcitriol
- Vitamin D2: ergocalciferol
- Vitamin D3: Cholecalciferol
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What must general Vitamin D be transformed to in the liver and kidney?
- Liver: Calcidiol
- Kidney: Calcitriol
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What happens with the PTH with increased vitamin D and increased Ca?
PTH is inhibited
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Where does the PTH work, kidney or liver?
Kidney to produce Calcitriol
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What are the effects of calcitriol in the kidney? (4)
- Increase intestinal Ca absorption
- Mobilize Ca from bone
- increase renal absorption of Ca
- decrease Renal excretion of Ca
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What causes calciuria?
- Excess NaCl
- Problem with older women due to loss of estrogen
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What can counterbalance the NaCl effect ad Calcuria?
Potassium Citrate
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How does the thyroid gland effect Ca?
- When Ca is high, the thyroid gland releases calcitriol
- Calcitriol stops Ca bone mobilization
- Allows Vit. D to be used in other body systems
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What part of the bone is most susceptible to Osteo.?
Trabecular (center, spongy)
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When does Osteopenia become osteoporosis?
When BMD <-2.5
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What happens to Ca and Vit. D levels with aging?
They both decrease
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At what age should we worry about a low BMD?
30, b/c this is when we should be at our peak BMD
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What are the three risk factors for osteoporesis?
- 1) Age
- 2) BMD level low at age 30
- 3) Menopause
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What should you supplement with if you suffer from osteoporosis?
Vitamin D + Calcium
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Why is exercise important to inhibit osteoporosis?
It increases bone density
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