Vitamin A Flashcards
What do retinoids include
- retinol - retinal - retinoic acid - retinyl esters - synthetic analogues
Examples of sources of Vitamin A
liver, dairy, fish, eggs
Stability of Vitamin A
degraded by oxygen light and heat
Bioavailability of Vitamin A
70-90% of Vitamin A is absorbed as long as the meal contains at least 10 g of FAT
During digestion of Vitamin A, what is retinol typically bound to?
fatty acid esters
what are the retinyl esters complexed with in the diet
proteins
how is retinol absorbed
the protein + retinyl esters need to be removed
how is the protein and retinyl ester removed?
by proteolytic enzymes in ST or duo.
what do retinol esters form once they are released from the proteins
fat globules
why do retinol esters form fat globules
because they are fat soluble
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
where is vitamin A absorbed?
in the duod and jejun
what is vitamin A absorbed by?
low doses - protein carrier high doses - passive diffusion
True or false - vitamin A can be absorbed through the skin
TRUE - topical applications
What does retinol require for transportation
esterification
what is esterification in the transport of retinol regulated by?
cellular retinol binding protein (CRBP)II
how is retinol bound to CRBP II converted to retinyl esters
LRAT ARAT
what are retinyl esters in the enterocyte incorporated into for transport
chylomicrons
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
When needed, what do retinyl esters do?
they are transported out of the liver in the blood via RBP and tranthyretin
what do RBP and tranthyretin do
carry retinol fom liver back to extrahepatic tissue
why is RBP bound to tranthyretin?
to prevent its filtration by the kidney
RBP levels are dependent on what
protein, retinol, zinc
True or false retinoic Acid can enter circulation through portal vein
true - it is bound to albumin for transport. retinol CANNOT
Where is esterified retinol stored
in the liver bound to CRBP - in the stellate cells- (some also in parenchymal)
The liver contains ___ of the bodys total vitamin A stores
90% - about 500,000IU in storage - able to last several years.
When does hypervitaminosis A develop
when stellate cells cannot take up anymore vitamin A and as a result serum levels start to rapidly increase
Is retinol or retinoic acid involved in dark adaptation
retinol
how is retinol transported to the retina
via circulation - where it moves into retinal pigment epithelial cells
what happens when retinol arrives at retinal pigment epithelial cells
LRAT converts retinol into all-trans retinyl esters - that can be stored
when retinyl esters are needed- what are they converted to
11-cis retinOL - and then into 11-cis retinAL
11-cis retinal is transported where?
rod cells
once in a rod cell, 11-cis retinal combines with what?
opsin
11-cis retinal + opsin
rhodopsin
once a photon is absorbed 11- cis retinal is converted to what?
11-trans retinal
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)
all-trans retinal is converted to what?
all trans retinol
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
how is vitamin A involved with normal cell differentiation
maintenance of integrity and function of epithelial tissues
What happens to squamous and keratinized cells during vitamin A deficiency
they increase
what happens to mucous secreting collumnar and cuboidal cells during vitamin A deficincy
they decrease
What type of immunity is Vitamin A involved in
humoral and cell mediated immunity WBC differentiation, activation of T-lymphocytes
Retinol or retinoic acid are required for spermatogenesis
RETINOL
during excretion retinol is oxidized and conjugated to make what
polar, non soluble metabolites
after retinol is oxidized and conjugated into polar non soluble metabolites, where is it exctreted?
60% urine 40% feces
Vitamin A deficiency is common in what age group
children under the age of 5 in developing worlds
Symptoms of Vitamin A deficiency
follicular hyperkeratinosis
delayed growth
impaired spermatogenesis
increased infections blindness
children who are deficient in vitamin A have a higher incidence of what?
respiratory disease and diarrhea + mortality
what is the leading cause of blindness in developing worlds?
vitamin A deficiency
what is the earliest evidence of vitamin A def
impaired dark adaptaion
mild vitamin A deficiency results in what
changes in the conjunctiva called Bitots spots
what do disappearance of goblet cells in conjuctiva result in
dryness from inadequate mucin production
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
severe or prolonged Vitamin A deficiency can result in what
xerophthalmia (dry eyes)
what is xerophthalmia characterized by
changes in cells of the cornea that result in corneal ulcers, scarring, and blindness
who has an increased risk of vitamin A deficiency
- hypothyroidism
- fat malabsorptive disorders
- LV or GB dz
- renal dz
- protein malnutr
- alcoholics
Clinical indications of Vitamin A supplementation
- retinitis pigmentosa
- diseases of the skin
- acute promyelocytic leukemia
Toxicuty of cause by the overconsumption of vitamin a or carotenoids
vitamin a
true or false, with vitamin A supplementation, teratogenicity is reported in newborn babies, therefore high doses are CI in pregnant women
true
early warning signs of vitamin A toxicity
- dry skin
- fatigue
- headache
- jt, mm, bone pain
Conraindications
- high doses in pregnant women
- end stage renal dz
- lv dz
- malnutrition
- alcoholism
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
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
What happens to iron when there is Vitamin A deficiency
there is decrease iron incorporation into RBCs
___ is required as a cofactor for the conversion of retinol to retinal
Zn
What does the RDR test?
measures plasma retinol levels before and 5 hours after oral administration
