Vitamin A Flashcards
(22 cards)
What is Vitamin A?
-A fat soluble vitamin that is stored in the body
Vitamin A is …
-retinol (alcohol) or retinal (aldehyde)
What has the highest Vitamin A activity?
-B-carotene
What are the food sources of preformed vitamin A retinoids?
-egg yolk, dairy products (milk fat), organ meats and meats, fatty fish oils, fortified foods
What are the food sources of provitamin A?
-dark green and yellow fruits and vegetables
-ex. Spinach, carrots, sweet potato, squash, cantaloupe
What are factors that influence vitamin A absorption?
-intestinal parasite infections
-acute diarrhea in children
-bowel resections
-pancreatic disease and cystic fibrosis
-low dietary fat intake
-zinc deficiency and iron deficiency
-protein malnutrition
What is the plasma transporter for vitamin A?
-retinol binding protein (RBP)
Summarize the function of Retinoid binding protein (RBP)
-The relative abundance of RBP is highest in liver
-in plasma, RBP function to solubulize retinol and to deliver it to cells
-RBP concentrations vary with disease (PEM, liver diseases, Vitamin A deficiency)
Summarize the function of cellular retinol binding protein
-As in plasma, inside the aqueous environment of the cell, vitamin A is bound to protein
-CRBPI and CRBPII: Ligand- all trans-retinol (1 and 2), all trans-retinal(2)
Summarize the function of cellular retinoid-binding protein
-two forms of cellular retinoic acid -binding protein CRABP-I and CRABP-II
What are the functions of Vitamin A?
-Vision, immune function, epithelial cell differentiation, gene regulation, bone growth(bone growth will not be covered)
What other deficiency usually coexists with Vitamin A deficiency?
-Iron deficiency
What is associated with decreased RBP?
-Protein Malnutrition
Where is CRBP-I found and what does it bind to?
-Found in liver, kidneys, testes, and other tissues
-binds to all-trans-retinol
Where is CRBP-II found and what does it bind to?
-Found in enterocytes bind both all trans-retinol and retinal
Describe the process of dark adaptation
-Light exposure of rhodopsin causes dissociation of retinal from opsin in a process called “bleaching”
-Bright light thus will cause rhodopsin to be broken down(so eyes need time to adapt to light(rhodopsin regeneration takes place in darkness))
-Gradual increase in sight from bright light to dark room is linked to regeneration of rhodopsin in the rod cells
Describe Vitamin A’s role in immunity
-Plays central role in development and differentiation of white blood cells
-required to maintain skin and muscosal cells: this cells function as a barrier against infections and first line of defense
-Keratinization of muscous membranes can result in vitamin A deficiency and increase risk of infection
What type of protein is RBP?
-a negative “acute phase protein”
-it decreases in inflammation and serves as a marker of inflammation
-Vitamin A deficiency results in decreased concentration of RBP leading to further detrimental affects on the immune system
What happens to Mucus Cells without Vitamin A?
-They become filled with keratin and become dry and hard
What are indicators of Vitamin A deficiency?
-Eye Signs: Conjuctival Xerosis with Bitot’s Spots in young children
-dietary assessment
-epithelial cell differentiation (inc. keratin forming cells)
-impaired reproductive capacity and immune function
What are the Ocular signs of Vitamin A deficiency?
-Bitot’s spots(conjuctival scratches); Conjuctival and Corneal Xerosis(drying); Keratomalacia (corneal necrosis/ulceration); Nyctolopia (night blindness)
What are biochemical indicators of Vitamin A deficiency?
Vitamin A or RBP is low in plasma, breast milk, tears
-low plasma RBP
-Liver total retinol is gold standard but not practical for humans
