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)
What is the common structures of Vit E?
Chromanol ring + a-Tocopherol
What Vit E for has the highest F?
a-tocopherol
What are the sources of Vit E?
a-tocopherol
1 a-tocopherol equivalent (TE) = 1 mg of a-tocopherol
What is the primary function of Vit E?
Maintenance of membrane integrity in body cells by preventing oxidative destruction (perioxidation) of FA contained in phospholipids of the cellular membranes
What tissues are susceptible to oxidation?
Lungs, Brain, RBC
How is vitamin E regenated?
The reduction of vitamin E back to its antioxidant form requires vitamin C, reduced glutathionine (GSH), and NADPH
What is the synthetic form of Vit K? Natural?
Menadione (K3)
Phylloquinone (K1) - Plants
Menaquinone (K2) - Bacteria and animal
What is the primary function of Vitamin K?
Required as an enzymatic cofacotr involved in the carboxylation of glutamate residues on the N-terminal portion of important precursor proteins; forms y-carboxyglutamate
Sources of Vitamin K?
Dark green leafy veggies
What patient population is at risk for vit K def?
Neborn infant and people who have been injured or treated chronically with antibiotics (destruction of GTI bacteria that synthesize vit)
