Block 2: ADEK Flashcards
What are the components of vitamin A?
beta-ionone rign with an isoprenoid chain
What are the forms of Vitamin A?
- Retinol (alcohol) - vision
- Retinal (aldehyde) - vision
- Retinoic acid (acid) - growth and differentiation
What is the precursor or Vit A? And its precursor?
Gamma carotene -> beta-carotene -> vit A
Describe the conversion of b-carotene to retinol?
B-caroten is cleaved by 15, 15-carotenoid dioxygenase to form retinal (theoretically forms 2 retinal however doesn’t happen in vivo)
How much of b-carotene is lost in the intestine without being converted to retinol?
> 30%
Conversion of food source dietary vitamin A (retinol)
Dietary or supplementary 1 μg → 1 μg retinol
Supplementary β-carotene (oily) 2 μg → 1 μg retinol
Dietary β- carotene (food) 12 μg → 1 μg retinol
Dietary ⍺-carotene (food) 24 μg → 1 μg retinol
How is Vit A absorbed into the body?
Chylomicron remnant deliver retinyl esters and part of carotenoids to liver -> hydrolyzed to retinol by binding to CRPB and transported to tissues (stellate cells)
What are the functions of VitA?
Retinol and retinal: Vision
Retinoic acid: Embroyonic devo and repro, bone metabolism, hematopoiesis (cell growth and proliferation)
How does vit a contribute to vision?
- When light hits retinal portion of rhodopsin it shapes shape (isomerization back to trans form)
- All trans retinal formed is converted to 11-cis retinal
What are the gene transcription receptors of Vit A? MOA?
- RAR
- RXR
- Retinoic acid binds to receptors inducing dimerization where confo change causes co-receptors to dissociate from receptor
- Receptors can bind to responce elements on DNA and upregulate or down the expression of target gene
Sources of Vit A?
Liver and carrots
Def of Vit A?
- Growth retardation
- Infections
- Keritinization
- Xeropthalamia (Bitots spot)
Toxicity of Vit A?
10x RDA -> hypervitaminosis A
What are the forms of Vit D?
Vit D2 (ergocalciferol)
Vit D3 (cholecalciferol)
Describe the synthesis cholecalciferol?
Irradiation of 7-dehydrocholesterol (intermediate in cholesterol synthesis) from sunlight to previtamin D3 -> 2-3 days to D3 -> transported through skin to blood by DBP
How is 7-dehydrocholesterol synthesized?
Sebaceous glands of the skin secreted onto the surface and reabsorbed into the epidermis
Describe the activation of Vit D3?
In the liver, 24,25-hydroxyl form is the inactive form that gets converted to the 1,25 form which is active
What is the primary function of calcitriol?
Increased absorption of Ca2+ and P:
1. Carried into the nucleus of the enterocyte where it binds to receptor proteins and acts as a steroid hormone
Describe the activity of calcitriol?
- Stimulates and synthesizes of new mRNA
- mRNA is translated to calbindin (protein)
- Calbindin is a calcium binding protein in the intestinal mucosa required for Ca2+ transport across cell membranes
What are the signs of Vitamin D def?
Due to inadequate intake or sunlight exposure:
1. Rickets in children
2. Osteomalacia in adults
3. Osteoporosis
Increase high BP and CV risk
What are signs of vit D tox?
Hypervitaminosis D from OD
* excessive exposure to sun doesn’t cause tox by overproduction of endogenous cholecalciferol
* Hypercalcemia
What are sx of Vit D poisoning
- Dehydration
- V
- Anorexia
- Irritability
- C
- Fatigue
What is the receptor of Vit D?
Vitamin D receptor (VDR), a type 1 nuclear receptor and DNA transcription factor
What are the classes of Vit E?
- Tocopherols (saturated side chains)
- Tocotrienols (unsaturated side chains)
