Vitamin A Flashcards Preview

Nutrition 1 Part 2 > Vitamin A > Flashcards

Flashcards in Vitamin A Deck (66):
1

What do retinoids include

- retinol - retinal - retinoic acid - retinyl esters - synthetic analogues

2

Examples of sources of Vitamin A

liver, dairy, fish, eggs

3

Stability of Vitamin A

degraded by oxygen light and heat

4

Bioavailability of Vitamin A

70-90% of Vitamin A is absorbed as long as the meal contains at least 10 g of FAT

5

During digestion of Vitamin A, what is retinol typically bound to?

fatty acid esters

6

what are the retinyl esters complexed with in the diet

proteins

7

how is retinol absorbed

the protein + retinyl esters need to be removed

8

how is the protein and retinyl ester removed?

by proteolytic enzymes in ST or duo.

9

what do retinol esters form once they are released from the proteins

fat globules

10

why do retinol esters form fat globules

because they are fat soluble

11

what happens to the fat globules after release from retinol esters

bile and phospholipids help emulsify to form micelles. brush border enzymes break off fatty acid chains to form free retinol

12

where is vitamin A absorbed?

in the duod and jejun

13

what is vitamin A absorbed by?

low doses - protein carrier high doses - passive diffusion

14

True or false - vitamin A can be absorbed through the skin

TRUE - topical applications

15

What does retinol require for transportation

esterification

16

what is esterification in the transport of retinol regulated by?

cellular retinol binding protein (CRBP)II

17

how is retinol bound to CRBP II converted to retinyl esters

LRAT ARAT

18

what are retinyl esters in the enterocyte incorporated into for transport

chylomicrons

19

what do chylomicrons carry the retinyl esters to?

peripheral cells and tissues in the body. the remaining retinyl esters are then brought to the liver in the chylomicron remnants

20

When needed, what do retinyl esters do?

they are transported out of the liver in the blood via RBP and tranthyretin

21

what do RBP and tranthyretin do

carry retinol fom liver back to extrahepatic tissue

22

why is RBP bound to tranthyretin?

to prevent its filtration by the kidney

23

RBP levels are dependent on what

protein, retinol, zinc

24

True or false retinoic Acid can enter circulation through portal vein

true - it is bound to albumin for transport. retinol CANNOT

25

Where is esterified retinol stored

in the liver bound to CRBP - in the stellate cells- (some also in parenchymal)

26

The liver contains ___ of the bodys total vitamin A stores

90% - about 500,000IU in storage - able to last several years.

27

When does hypervitaminosis A develop

when stellate cells cannot take up anymore vitamin A and as a result serum levels start to rapidly increase

28

Is retinol or retinoic acid involved in dark adaptation

retinol

29

how is retinol transported to the retina

via circulation - where it moves into retinal pigment epithelial cells

30

what happens when retinol arrives at retinal pigment epithelial cells

LRAT converts retinol into all-trans retinyl esters - that can be stored

31

when retinyl esters are needed- what are they converted to

11-cis retinOL - and then into 11-cis retinAL

32

11-cis retinal is transported where?

rod cells

33

once in a rod cell, 11-cis retinal combines with what?

opsin

34

11-cis retinal + opsin

rhodopsin

35

once a photon is absorbed 11- cis retinal is converted to what?

11-trans retinal

36

once photon is absorbed, what happens to the opsin attached to the retinal

it is separated as a nerve impulse is sent to the optic cortex of the brain ( via optic nerve)

37

all-trans retinal is converted to what?

all trans retinol

38

after all trans retinal is converted to all trans retinol, it is released from what? and to where?

rod cells - back into pigment epithelium of retina - where it can be converted to cis-retinal

39

how is vitamin A involved with normal cell differentiation

maintenance of integrity and function of epithelial tissues

40

What happens to squamous and keratinized cells during vitamin A deficiency

they increase

41

what happens to mucous secreting collumnar and cuboidal cells during vitamin A deficincy

they decrease

42

What type of immunity is Vitamin A involved in

humoral and cell mediated immunity WBC differentiation, activation of T-lymphocytes

43

Retinol or retinoic acid are required for spermatogenesis

RETINOL

44

during excretion retinol is oxidized and conjugated to make what

polar, non soluble metabolites

45

after retinol is oxidized and conjugated into polar non soluble metabolites, where is it exctreted?

60% urine 40% feces

46

Vitamin A deficiency is common in what age group

children under the age of 5 in developing worlds

47

Symptoms of Vitamin A deficiency

follicular hyperkeratinosis

delayed growth

impaired spermatogenesis

increased infections blindness

48

children who are deficient in vitamin A have a higher incidence of what?

respiratory disease and diarrhea + mortality

49

what is the leading cause of blindness in developing worlds?

vitamin A deficiency

50

what is the earliest evidence of vitamin A def

impaired dark adaptaion

51

mild vitamin A deficiency results in what

changes in the conjunctiva called Bitots spots

52

what do disappearance of goblet cells in conjuctiva result in

dryness from inadequate mucin production

53

what does inadequate mucin production in the eyes result in

enlargement and keratinization of epithelial cells and the appearance of bitots spots over the keratinized epithelia

54

severe or prolonged Vitamin A deficiency can result in what

xerophthalmia (dry eyes)

55

what is xerophthalmia characterized by

changes in cells of the cornea that result in corneal ulcers, scarring, and blindness

56

who has an increased risk of vitamin A deficiency

- hypothyroidism

- fat malabsorptive disorders

- LV or GB dz

- renal dz

- protein malnutr

- alcoholics

57

Clinical indications of Vitamin A supplementation

- retinitis pigmentosa

- diseases of the skin

- acute promyelocytic leukemia

58

Toxicuty of cause by the overconsumption of vitamin a or carotenoids

vitamin a

59

true or false, with vitamin A supplementation, teratogenicity is reported in newborn babies, therefore high doses are CI in pregnant women

true

60

early warning signs of vitamin A toxicity

- dry skin

- fatigue

- headache

- jt, mm, bone pain

61

Conraindications

- high doses in pregnant women

- end stage renal dz

- lv dz

- malnutrition

- alcoholism

62

ACUTE signs and sx of hyperviatminosis A

increase intracranial pressure n/v altered mental status H/A dizzy double vision weak jt, mm, bone pain

63

CHRONIC signs and sx of hyperviatminosis A

increase intracranial pressure ataxia anorexia H/A dry itchy skin alopecia, brittle nails conjunctivitis jt, mm, bone pain bone fractures LV damage

64

What happens to iron when there is Vitamin A deficiency

there is decrease iron incorporation into RBCs

65

___ is required as a cofactor for the conversion of retinol to retinal

Zn

66

What does the RDR test?

measures plasma retinol levels before and 5 hours after oral administration