Vitamin A

Question 1

What is Vitamin A?

Answer 1

-A fat soluble vitamin that is stored in the body

Question 2

Vitamin A is …

Answer 2

-retinol (alcohol) or retinal (aldehyde)

Question 3

What has the highest Vitamin A activity?

Answer 3

-B-carotene

Question 4

What are the food sources of preformed vitamin A retinoids?

Answer 4

-egg yolk, dairy products (milk fat), organ meats and meats, fatty fish oils, fortified foods

Question 5

What are the food sources of provitamin A?

Answer 5

-dark green and yellow fruits and vegetables
-ex. Spinach, carrots, sweet potato, squash, cantaloupe

Question 6

What are factors that influence vitamin A absorption?

Answer 6

-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

Question 7

What is the plasma transporter for vitamin A?

Answer 7

-retinol binding protein (RBP)

Question 8

Summarize the function of Retinoid binding protein (RBP)

Answer 8

-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)

Question 9

Summarize the function of cellular retinol binding protein

Answer 9

-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)

Question 10

Summarize the function of cellular retinoid-binding protein

Answer 10

-two forms of cellular retinoic acid -binding protein CRABP-I and CRABP-II

Question 11

What are the functions of Vitamin A?

Answer 11

-Vision, immune function, epithelial cell differentiation, gene regulation, bone growth(bone growth will not be covered)

Question 12

What other deficiency usually coexists with Vitamin A deficiency?

Answer 12

-Iron deficiency

Question 13

What is associated with decreased RBP?

Answer 13

-Protein Malnutrition

Question 14

Where is CRBP-I found and what does it bind to?

Answer 14

-Found in liver, kidneys, testes, and other tissues
-binds to all-trans-retinol

Question 15

Where is CRBP-II found and what does it bind to?

Answer 15

-Found in enterocytes bind both all trans-retinol and retinal

Question 16

Describe the process of dark adaptation

Answer 16

-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

Question 17

Describe Vitamin A’s role in immunity

Answer 17

-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

Question 18

What type of protein is RBP?

Answer 18

-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

Question 19

What happens to Mucus Cells without Vitamin A?

Answer 19

-They become filled with keratin and become dry and hard

Question 20

What are indicators of Vitamin A deficiency?

Answer 20

-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

Question 21

What are the Ocular signs of Vitamin A deficiency?

Answer 21

-Bitot’s spots(conjuctival scratches); Conjuctival and Corneal Xerosis(drying); Keratomalacia (corneal necrosis/ulceration); Nyctolopia (night blindness)

Question 22

What are biochemical indicators of Vitamin A deficiency?

Answer 22

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