Term
|
Definition
D2: ergocalciferol
D3: cholecalciferol |
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Term
| Where is Ergocalciferol found? |
|
Definition
Plants, fungi, molds, snails, worms
Ergosterol (UV)--> ergocalciferol D2 |
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Term
|
Definition
| Form found in animals and humans *lanolin (sheep) |
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Term
|
Definition
Produced in the skin by UVB-mediated photolytic non-enzymatic rx.
Lanolin--> previtamin D3
via 7-dehydrocholesterol |
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Term
|
Definition
undergoes a non enzymatic , thermal isomerization
previt d3--> vit d3 |
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Term
|
Definition
Bone health (levels of Ca and Phosphorous)
Promote bone mineralization
Monocyte macrophage, cell growth and differentiation |
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|
Term
| What is the major circulating form of Vit D? |
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Definition
| 25(OH)D (hormone), acts through VDR |
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Term
|
Definition
D3: 7 dehydrocholestorol vs D2: ergosterol
D3: production in humans: UV
D2: none in humans
D3: fully active in humans
D2: only 1/3 of D3 |
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Term
| Why do lifeguards not get Vit D poisoning? |
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Definition
| Previtamin D2 is thermaly unstable. Sunlight itself regulated formation. Extra is converted to lumisterol, tachysterol, etc. |
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Term
| Genomic action of 1,25 (OH)2 D |
|
Definition
- Binds to nuclear receptor (VDR nuc)
- Forms heterodimer with nuclear retinoid x receptor (RXR)
- Interacts with Vit D response element (VDRE) on DNA
- Modulates mRNA production of protein which increase calcium absorption is small intestine |
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Term
| Genomic action of 1,25 (OH)2 D--> outcome? |
|
Definition
| Modulated mRNA production of protein which increase calcium absorption in small intestine |
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Term
|
Definition
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|
Term
| Good food sources of Vit D? |
|
Definition
|
|
Term
|
Definition
19-50: 5 mcg
51-69: 10 mcg
70+ : 15 mcg |
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|
Term
| Vit D: conversion to active form |
|
Definition
Liver: 25 hydroxylase --> 25 (OH)D
Kidneys:
1 α hydroxylase --> 1,25 (OH)2 D
24-hydroxylase
- activated by 1,25 (OH)2D
- involved in catabolism of 1,25 (OH)2D to water soluble biologically inactive calcitroic acid |
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Term
| Active hormone form of Vit D? |
|
Definition
|
|
Term
| Major circulating form of Vit D? |
|
Definition
|
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Term
| Rate Limiting Enzyme in Vit D transformation? |
|
Definition
25-hydroxycalciferol-1-hydroxylase
- in proximal tubular epithelial cell of kidneys
+ by PTH (parathyroid hormone)
- by circulating fiberoblast growth factor 23 (FGF23)--> made by OSTEOCYTES
Gene: CYP27B1 hydroxylase |
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|
Term
| 1,25 (OH)2 D and Blood Ca [ ] |
|
Definition
↑ Ca absorption in Small Int.
- 1,25 (OH)2 D interacts with (VDR-RXR) receptor to
- ↑ expression of epithelial Ca channel protein (TRPV6)
- ↑ expression of the CaBP (Calbindin)
Calcium resorption
- ↑ expression of RANKL
RANK binds RANKL --> preosteoclasts to become mature osteoclasts
- mature osteoclasts remove Ca 2+ and HPO 4 2- from bone, maintaining Ca and P levels in blood. |
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Term
| How does body regulate plasma Ca? |
|
Definition
Parathyroid gland
- drop in serum Ca --> ↑ PTH
Role of PTH
- ↑ formation of active Vit D
Role of Vit D
- ↑ Ca absorption
- ↑ reabsorption of Ca by kidney
- ↑ bone resorption |
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|
Term
| 1, 25 (OH)2D and monocyte/marcophage? |
|
Definition
CD: cathelicidin, produced by monocyte/marcophage to respond to pathogen
1,25 (OH)2D ↑ expression of CD. May, also activate T and B lymphocytes and regulate cytokine and immonoglobulin synthesis |
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Term
| Rickets VS Osteomalacia (deficiency of vit D) |
|
Definition
Rickets (children)
Osteomalacia (Adults)
Ricket: enlargement of growth plate
stunted growth
Frontal and occipital bossing of head
- beading of ribs
- flaring of lower rib cage
Osteomalacia: softening of the bones due to defective bone mineralization.
Weak bones
Bone pain
Spinal bone pain
Pelvic bone pain
Leg bone pain
Muscle weakness
Hypocalcemia |
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Term
|
Definition
HYPOcalcemia
HYPOphosphatemia
↑ PTH
↑ serum alkaline phosphatase activity |
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Term
| What is the Minimal dose of UV B radiation? |
|
Definition
| (o.5 min erythemal dose) 3000 IU of Vit D3 |
|
|
Term
| What factors influence sun exposure? |
|
Definition
| Season, latitude, time of day, cloud voer, smog, sunscreen. |
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Term
| What groups are at risk of Vit D deficiency? Why? |
|
Definition
| Breast fed infants, older adults (skin cannot synthesize vit D efficiently and kidneys are less able to convert D to active hormone), limited sun exposure (alaska, religious reasons), dark skin (incr melanin), fat malabsorption, gastric by pass (alter circulation, small intestine where its absorbed) |
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Term
|
Definition
| Inadequate Ca intake. Inadequate Vit D inatake reduces Ca absoprtion. |
|
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Term
|
Definition
| Nausea, vomit, poor appetite, consipation, weakness, weight loss. Raise Ca levels in blood. Deposits of Ca and P in kidneys and soft tissues. |
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|
Term
| Current US vit D intake and status? |
|
Definition
| Optimal: 25(OH)D >37.5 (>15 ng/ml) |
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|
Term
| What is used to assess Vit D status? |
|
Definition
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