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Biochemistry: Vitamin D
Vitamin D
30
Chemistry
Graduate
05/16/2010

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Cards

Term
What are fomrs of Vit D?
Definition
D2: ergocalciferol
D3: cholecalciferol
Term
Where is Ergocalciferol found?
Definition
Plants, fungi, molds, snails, worms
Ergosterol (UV)--> ergocalciferol D2
Term
Cholecalciferol
Definition
Form found in animals and humans *lanolin (sheep)
Term
7-dehydrocholesterol
Definition
Produced in the skin by UVB-mediated photolytic non-enzymatic rx.
Lanolin--> previtamin D3
via 7-dehydrocholesterol
Term
Previtamin D3
Definition
undergoes a non enzymatic , thermal isomerization
previt d3--> vit d3
Term
Function of Vit D
Definition
Bone health (levels of Ca and Phosphorous)
Promote bone mineralization

Monocyte macrophage, cell growth and differentiation
Term
What is the major circulating form of Vit D?
Definition
25(OH)D (hormone), acts through VDR
Term
Vit D3 vs D2
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
Term
Why do lifeguards not get Vit D poisoning?
Definition
Previtamin D2 is thermaly unstable. Sunlight itself regulated formation. Extra is converted to lumisterol, tachysterol, etc.
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
Term
Genomic action of 1,25 (OH)2 D--> outcome?
Definition
Modulated mRNA production of protein which increase calcium absorption in small intestine
Term
One mcg is how many IU?
Definition
40
Term
Good food sources of Vit D?
Definition
Cod liver oild
Salmon
Egg
Term
Recommendation of Vit D?
Definition
19-50: 5 mcg
51-69: 10 mcg
70+ : 15 mcg
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
Term
Active hormone form of Vit D?
Definition
1,25 (OH)2D
Term
Major circulating form of Vit D?
Definition
25 (OH) D
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
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.
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
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
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
Term
Lab findings in Rickets?
Definition
HYPOcalcemia
HYPOphosphatemia
↑ PTH
↑ serum alkaline phosphatase activity
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.
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)
Term
Vit D and Osteoporosis?
Definition
Inadequate Ca intake. Inadequate Vit D inatake reduces Ca absoprtion.
Term
Too much Vit D?
Definition
Nausea, vomit, poor appetite, consipation, weakness, weight loss. Raise Ca levels in blood. Deposits of Ca and P in kidneys and soft tissues.
Term
Current US vit D intake and status?
Definition
Optimal: 25(OH)D >37.5 (>15 ng/ml)
Term
What is used to assess Vit D status?
Definition
25 (OH) D
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