Determinarea Vitaminei A.docx

8/14/2019 Determinarea Vitaminei A.docx

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Determinarea vitaminei A

Descoperirea de vitamina A poate fi derivat de la cercetare datnd de la 1906, indicnd

faptul c ali factori dectcarbohidrati ,proteine , igrsimi au fost necesare pentru a menine

bovine sntoase. Deoarece "ap-solubil factorul B "(vitamina B ) a fost recent descoperit,

cercetatorii au ales numele de "grsime-solubil factorul A" (vitamina A). n 1919, Steenbock

(Universitatea din Wisconsin), a propus o relaie ntre pigmeni galben de plante (beta-caroten) si

vitamina A. Vitamina A a fost prima oara sintetizat in 1947 de doi chimiti olandeze, David

Adriaan van Dorp i Jozef Ferdinand Arens.

Vitamina A(retinol sau vitamina A, retinei, iar patru carotenoide , inclusivbeta-caroten )

este ovitamina care este nevoie deretinei a ochiului, n forma unui metabolit specific, moleculade lumin absoarberetiniene , care este necesar att pentru sczut -lumina (scotopic viziune) i

viziune de culoare . Vitamina A, de asemenea, funcioneaz ntr-un rol foarte diferite ca form

oxidat ireversibil deretinol cunoscut sub numelede acid retinoic , care este un important

hormon-ca factor de crestere pentruepiteliale celule i altele.

n alimente de origine animal, principala forma de vitamina A este unester , n

principalpalmitat de retinil , care este convertit laretinol (chimic unalcool ), n intestinul

subire. Funciile de retinol formular ca o form de depozit de vitamine, i pot fi convertite la ide la ei vizual activaldehida form,retinei . Acidul asociat (acid retinoic), un metabolit care

poate fi sintetizat ireversibil de vitamina A, vitamina are doar o activitate parial, i nu n funcie

de nivelul retinei pentru ciclul vizuale.

Toate formele de vitamina A au unbeta-ionone inel de la care unisoprenoid lan este ataat,

numit ungrupde retinil. Ambele caracteristici structurale sunt eseniale pentru activitatea de

vitamina, pigmentul portocaliu dinmorcovi -beta-caroten -poate fi reprezentat ca dou grupuri

de retinil conectate, care sunt utilizate n organism pentru a contribui la un nivel de vitamina.

alfa-caroten sigama- caroten au, de asemenea, un grup de retinil singur, ceea ce le da o oarecare

activitate de vitamina. Nici unul dintre celelalte caroten au activitate de vitamina. Carotenoide

beta-criptoxantindispune de un grup de ionone i are o activitate de vitamina la om.
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Vitamina A poate fi gsit n dou forme principale dealimente :

Retinolul , forma de vitamina A absorbit atunci cnd mnnc surse de alimentare deorigine animal, este un galben, grsime-solubil substan. Deoarece formularul de

alcool pur este instabil, vitamina se gaseste in tesuturile ntr-o form de ester de retinil.Acesta este, de asemenea, produs comercial i administrat ca esteri, cum ar fiacetat de

retinil saupalmitat .

Caroteni alfa-caroten, beta-caroten si gamma-caroten funcioneaz ca vitamina A laierbivorele i animale omnivor, care dein enzima necesare pentru a converti acesti

compusi laretinei . n general, sunt carnivore convertoare srace ale ionine care conin

carotenoizi, i carnivore pure, cum ar fi pisici i dihori domestici nu dispun debeta-

caroten 15,15 '-monooxygenase i nu se poate converti orice carotenoide a retinei

(rezultat n nici unadintre carotenoizi fiind forme de vitamina A pentru aceste specii).

Echivalene de retinoizisi carotenoide (UI)

Deoarece unele carotenoide pot fi convertite n vitamina A, ncercri au fost fcute

pentru a determina ct de mult din ele n dieta este echivalent cu o sum anumit de retinol,

astfel nct se pot face comparaii de beneficiul de diferite produse alimentare. Situaia poate fi

confuz, deoarece echivalene acceptate s-au schimbat. Timp de muli ani, un sistem de

echivalene n care ounitate internaional(UI) a fost egal cu 0,3micrograme de retinol, 0,6

micrograme de -caroten, sau de 1,2 micrograme de alte carotenoide provitamina A, a fost

folosit. Mai trziu, o unitate numit echivalent retinol (RE), a fost introdus. nainte de 2001, unul

RE corespundea micrograme retinol 1, 2 g -caroten dizolvat n ulei (acesta este numai parial

dizolvat n cele mai multe pastile de suplimente nutritive, datorit solubilitii foarte sraci, n

orice mediu), 6 g -caroten n alimente normale ( deoarece nu este absorbit, precum i atunci

cnd n uleiuri), i 12 micrograme, fie-caroten ,-caroten , sau -criptoxantina n produselealimentare.

Mai nou de cercetare a artat c absorbia de provitamina A de carotenoide este doar

jumtate la fel de mult ca sa crezut anterior. Ca urmare, n 2001, SUAInstitutul de Medicina a

recomandat o nou unitate, activitate echivalent retinol (RAE). Fiecare micrograme RAE
http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Food&usg=ALkJrhiA30H6ym3SGuLTRn_LdAY_lZlrTQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Food&usg=ALkJrhiA30H6ym3SGuLTRn_LdAY_lZlrTQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinol&usg=ALkJrhhWkTeb4cDfvbPFypoE4IE2tXvj3ghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinyl_acetate&usg=ALkJrhi7SonMuzcQoMMe-_tXqFI3Li5epAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinyl_acetate&usg=ALkJrhi7SonMuzcQoMMe-_tXqFI3Li5epAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinyl_acetate&usg=ALkJrhi7SonMuzcQoMMe-_tXqFI3Li5epAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinyl_palmitate&usg=ALkJrhi4FXIo_Dnqkm3YEn_ENijyf1I_zAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Carotene&usg=ALkJrhheZ1qXerT80gzo9hkYm_leIJKw3Ahttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinal&usg=ALkJrhjfdSL_HKZzRqTXRU_qtcC3ArI7CAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Beta-carotene_15,15%27-monooxygenase&usg=ALkJrhj--czvtlgDbmn1_vvURUYMLAkDighttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Beta-carotene_15,15%27-monooxygenase&usg=ALkJrhj--czvtlgDbmn1_vvURUYMLAkDighttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Beta-carotene_15,15%27-monooxygenase&usg=ALkJrhj--czvtlgDbmn1_vvURUYMLAkDighttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/International_unit&usg=ALkJrhhuvICOywthlGFwzS0QLdZK5w3rLAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/International_unit&usg=ALkJrhhuvICOywthlGFwzS0QLdZK5w3rLAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Microgram&usg=ALkJrhhTCFR9_GJpr0tAVm2iYb9bbK5DWwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Alpha-carotene&usg=ALkJrhg5sXANPVj58WK3vhzMSuFv0S_EkQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Alpha-carotene&usg=ALkJrhg5sXANPVj58WK3vhzMSuFv0S_EkQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Gamma-carotene&usg=ALkJrhiB1IJ0e__WVZzYBqBt8_z9qcmdEQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Gamma-carotene&usg=ALkJrhiB1IJ0e__WVZzYBqBt8_z9qcmdEQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Gamma-carotene&usg=ALkJrhiB1IJ0e__WVZzYBqBt8_z9qcmdEQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Cryptoxanthin&usg=ALkJrhgfKyxZN_V9X07jF5bgXa9xgwKe3Qhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Institute_of_Medicine&usg=ALkJrhgKJpobkV696MBC5JJwSMMGJCDVVwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Institute_of_Medicine&usg=ALkJrhgKJpobkV696MBC5JJwSMMGJCDVVwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Cryptoxanthin&usg=ALkJrhgfKyxZN_V9X07jF5bgXa9xgwKe3Qhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Gamma-carotene&usg=ALkJrhiB1IJ0e__WVZzYBqBt8_z9qcmdEQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Alpha-carotene&usg=ALkJrhg5sXANPVj58WK3vhzMSuFv0S_EkQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Microgram&usg=ALkJrhhTCFR9_GJpr0tAVm2iYb9bbK5DWwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/International_unit&usg=ALkJrhhuvICOywthlGFwzS0QLdZK5w3rLAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Beta-carotene_15,15%27-monooxygenase&usg=ALkJrhj--czvtlgDbmn1_vvURUYMLAkDighttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Beta-carotene_15,15%27-monooxygenase&usg=ALkJrhj--czvtlgDbmn1_vvURUYMLAkDighttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinal&usg=ALkJrhjfdSL_HKZzRqTXRU_qtcC3ArI7CAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Carotene&usg=ALkJrhheZ1qXerT80gzo9hkYm_leIJKw3Ahttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinyl_palmitate&usg=ALkJrhi4FXIo_Dnqkm3YEn_ENijyf1I_zAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinyl_acetate&usg=ALkJrhi7SonMuzcQoMMe-_tXqFI3Li5epAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinyl_acetate&usg=ALkJrhi7SonMuzcQoMMe-_tXqFI3Li5epAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinol&usg=ALkJrhhWkTeb4cDfvbPFypoE4IE2tXvj3ghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Food&usg=ALkJrhiA30H6ym3SGuLTRn_LdAY_lZlrTQ


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corespunde micrograme retinol 1, 2 g de -caroten n ulei, 12 g de "dietetic", beta-caroten, sau 24

micrograme de alte trei dietetice provitamina-A carotenoizi.

Deoarece conversia de retinol de carotenoide provitamina de ctre organismul uman este

reglementat n mod activ de ctre suma de retinol la dispoziia organismului, conversiile seaplic strict doar pentru vitamina A-deficit de oameni. Absorbia de provitamine depinde n

mare msur de cantitatea de lipide ingerate cu provitamina, lipide crete absorbia de

provitamina.

Concluzia care poate fi tras de cercetare noi este faptul c fructele i legumele nu sunt

la fel de utile pentru obinerea de vitamina A, aa cum a fost gandit, cu alte cuvinte, UI c aceste

alimente au fost raportate s conin au fost n valoare de mult mai puin dect acelai numr de

UI de grsime, uleiuri i dizolvate ntr-o anumit msur () suplimente. Acest lucru este

important pentruvegetarieni , caorbirea de noapte este rspndit n rile n care carnea de

puin sau vitamina A-fortificate alimente sunt disponibile.

O probvegan dieta pentru o zi, care ofer suficiente de vitamina A a fost publicat de

ctre Consiliul pentru Alimentaie i Nutriie .Pe de alt parte, valorile de referin pentru retinol

sau echivalentele sale, oferite deAcademia Nationala de Stiinte , au sczut. ADR (pentru

barbati) din 1968 a fost de 5000 UI (1500 retinol micrograme). n 1974, ADR a fost stabilit la1000 RE (1000 micrograme retinol), n timp ce acumaporturile de referin alimentareste de

900 RAE (900 micrograme sau 3000 UI retinol). Acest lucru este echivalent cu 1800

micrograme de -caroten supliment (3000 UI) sau de 10800 g de -caroten n alimente (18000

UI).
http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vegetarian&usg=ALkJrhh0pvfvTm5LFTZBGVovOK682fHnhAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Night_blindness&usg=ALkJrhgO3CzhPHbCOtwfxA-n1TmRQ_L_zwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vegan&usg=ALkJrhgqMreodMCVHzbyzmZNvnYXFdgXpwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vegan&usg=ALkJrhgqMreodMCVHzbyzmZNvnYXFdgXpwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/United_States_National_Academy_of_Sciences&usg=ALkJrhhlvkiPzaukaIwy1SU-3awmu2WXNwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Recommended_daily_allowance&usg=ALkJrhjT8BDTC_7zwzDo5xPos8Z5ffL9yQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Dietary_Reference_Intake&usg=ALkJrhhDyET27wUaFEOvtKvzvh46qMfExghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Dietary_Reference_Intake&usg=ALkJrhhDyET27wUaFEOvtKvzvh46qMfExghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Dietary_Reference_Intake&usg=ALkJrhhDyET27wUaFEOvtKvzvh46qMfExghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Dietary_Reference_Intake&usg=ALkJrhhDyET27wUaFEOvtKvzvh46qMfExghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Recommended_daily_allowance&usg=ALkJrhjT8BDTC_7zwzDo5xPos8Z5ffL9yQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/United_States_National_Academy_of_Sciences&usg=ALkJrhhlvkiPzaukaIwy1SU-3awmu2WXNwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vegan&usg=ALkJrhgqMreodMCVHzbyzmZNvnYXFdgXpwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Night_blindness&usg=ALkJrhgO3CzhPHbCOtwfxA-n1TmRQ_L_zwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vegetarian&usg=ALkJrhh0pvfvTm5LFTZBGVovOK682fHnhA


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Surse

Vitamina A se gaseste in mod natural in multe alimente:

ficat (de vita, porc, pui, curcan, pete) (6500 micrograme 722%), inclusivulei de ficat decod

Verzii ppdie(5588 UI 112%)[14] de morcovi (835 g 93%) broccoli frunze (800 g 89%) - PotrivitUSDA de baze de datebuchetelele de broccoli au

mult mai puin.[15]

cartofi dulci (709 micrograme 79%) unt (684 g 76%) varz(681 micrograme 76%) spanac (469 g 52%) dovleac (400 g 41%) varza (333 micrograme 37%) Brnz Cheddar(265 micrograme 29%) pepene galben pepene galben (169 micrograme 19%) ou (140 micrograme 16%) caise (96 micrograme 11%) papaya (55 micrograme 6%) mango (38 micrograme 4%) mazre(38 micrograme 4%) broccoli (31 micrograme 3%) lapte (28 micrograme 3%)

Not: datele preluate de laUSDA de baze de date valorile bracketate sunt echivalene de

retinol de activitate (RAEs) i procentul de adulti de sex masculinADR , la 100 degrame de

produs alimentar (medie).
http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Liver_(food)&usg=ALkJrhinGu7OgriDG8ZPydf0HNRjS3uulghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Cod_liver_oil&usg=ALkJrhh2VothBdjOgdbG3z3Qd7VaH9thaAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Cod_liver_oil&usg=ALkJrhh2VothBdjOgdbG3z3Qd7VaH9thaAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Cod_liver_oil&usg=ALkJrhh2VothBdjOgdbG3z3Qd7VaH9thaAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Taraxacum&usg=ALkJrhi4aHdtGIRP-xjKhjU63u-KLCHawwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Taraxacum&usg=ALkJrhi4aHdtGIRP-xjKhjU63u-KLCHawwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-13http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-13http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-13http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Carrot&usg=ALkJrhi23in73hwhSLxIYA_8N6RlTrs-gghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Broccoli&usg=ALkJrhiTMvVgnbMxMCLLyziOSNLmdnb1xAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://www.nal.usda.gov/fnic/foodcomp/search/&usg=ALkJrhgNXmI1HjwrbY-FcSI-Dhluzxg-zghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-14http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-14http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-14http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Sweet_potato&usg=ALkJrhi8JONUUm1nsPhLyvuAkvgwxOJicghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Butter&usg=ALkJrhi3Q8gh6nThRt4if4TKuitfcYRoAQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Kale&usg=ALkJrhh-WLLVAL74BvFQLEfKLE7OreVJEQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Kale&usg=ALkJrhh-WLLVAL74BvFQLEfKLE7OreVJEQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Spinach&usg=ALkJrhgrk0F2A2MHxTimuwCOHvEx-wd6ewhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Pumpkin&usg=ALkJrhheJZvBA7aGqfhbDZ0vSV84tvOg7ghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Collard_greens&usg=ALkJrhig5OO4W3_t_nI9ZYVUTJxAWO4_YAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Cheddar_cheese&usg=ALkJrhi35Rt6l6xZvPwPEPt8Cdwoa8NH7Ahttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Cheddar_cheese&usg=ALkJrhi35Rt6l6xZvPwPEPt8Cdwoa8NH7Ahttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Cantaloupe_melon&usg=ALkJrhhk089nSS69Jz5iV8Le_kr6Gt9jSghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Egg_(food)&usg=ALkJrhjLEYtp4UKPPb2zGWrNVUWUx5Wg-Ahttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Apricot&usg=ALkJrhhygzo0lfxpZoirxAi3Y8rJ8No6Xwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Papaya&usg=ALkJrhgzhWWGFIu8OE-AnRJMucQwQ1Gs2Qhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Mango&usg=ALkJrhg6fnBbTX6D-gX-LysZ8Tvzgk5U3ghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Pea&usg=ALkJrhjEuAQQKS8dMy7N4mfjay04KYX17whttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Pea&usg=ALkJrhjEuAQQKS8dMy7N4mfjay04KYX17whttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Broccoli&usg=ALkJrhiTMvVgnbMxMCLLyziOSNLmdnb1xAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Milk&usg=ALkJrhipSQBplv_YLC-bg9GQ51wRaWc0pwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://www.nal.usda.gov/fnic/foodcomp/search/&usg=ALkJrhgNXmI1HjwrbY-FcSI-Dhluzxg-zghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://www.nal.usda.gov/fnic/foodcomp/search/&usg=ALkJrhgNXmI1HjwrbY-FcSI-Dhluzxg-zghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Recommended_Dietary_Allowance&usg=ALkJrhj5nx6XjQCd4wBkEwllIGd4bbiksAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Recommended_Dietary_Allowance&usg=ALkJrhj5nx6XjQCd4wBkEwllIGd4bbiksAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Gram&usg=ALkJrhgqgRIRn1Hhl_S1jZV1Mgqp4Qoi6ghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Gram&usg=ALkJrhgqgRIRn1Hhl_S1jZV1Mgqp4Qoi6ghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Recommended_Dietary_Allowance&usg=ALkJrhj5nx6XjQCd4wBkEwllIGd4bbiksAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://www.nal.usda.gov/fnic/foodcomp/search/&usg=ALkJrhgNXmI1HjwrbY-FcSI-Dhluzxg-zghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Milk&usg=ALkJrhipSQBplv_YLC-bg9GQ51wRaWc0pwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Broccoli&usg=ALkJrhiTMvVgnbMxMCLLyziOSNLmdnb1xAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Pea&usg=ALkJrhjEuAQQKS8dMy7N4mfjay04KYX17whttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Mango&usg=ALkJrhg6fnBbTX6D-gX-LysZ8Tvzgk5U3ghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Papaya&usg=ALkJrhgzhWWGFIu8OE-AnRJMucQwQ1Gs2Qhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Apricot&usg=ALkJrhhygzo0lfxpZoirxAi3Y8rJ8No6Xwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Egg_(food)&usg=ALkJrhjLEYtp4UKPPb2zGWrNVUWUx5Wg-Ahttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Cantaloupe_melon&usg=ALkJrhhk089nSS69Jz5iV8Le_kr6Gt9jSghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Cheddar_cheese&usg=ALkJrhi35Rt6l6xZvPwPEPt8Cdwoa8NH7Ahttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Collard_greens&usg=ALkJrhig5OO4W3_t_nI9ZYVUTJxAWO4_YAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Pumpkin&usg=ALkJrhheJZvBA7aGqfhbDZ0vSV84tvOg7ghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Spinach&usg=ALkJrhgrk0F2A2MHxTimuwCOHvEx-wd6ewhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Kale&usg=ALkJrhh-WLLVAL74BvFQLEfKLE7OreVJEQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Butter&usg=ALkJrhi3Q8gh6nThRt4if4TKuitfcYRoAQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Sweet_potato&usg=ALkJrhi8JONUUm1nsPhLyvuAkvgwxOJicghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-14http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://www.nal.usda.gov/fnic/foodcomp/search/&usg=ALkJrhgNXmI1HjwrbY-FcSI-Dhluzxg-zghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Broccoli&usg=ALkJrhiTMvVgnbMxMCLLyziOSNLmdnb1xAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Carrot&usg=ALkJrhi23in73hwhSLxIYA_8N6RlTrs-gghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-13http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Taraxacum&usg=ALkJrhi4aHdtGIRP-xjKhjU63u-KLCHawwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Cod_liver_oil&usg=ALkJrhh2VothBdjOgdbG3z3Qd7VaH9thaAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Cod_liver_oil&usg=ALkJrhh2VothBdjOgdbG3z3Qd7VaH9thaAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Liver_(food)&usg=ALkJrhinGu7OgriDG8ZPydf0HNRjS3uulg


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Funciilor metabolice

Vitamina A joaca un rol ntr-o varietate de funcii de pe tot corpul, cum ar fi:

Viziune

Gene transcriere Funcia imunitar Dezvoltrii embrionare i de reproducere Metabolismului osos Hematopoieza Si sanatatea pielii celulare Antioxidant de activitate

Viziune

Rolul de vitamina A n ciclul vizual este legat de forma retinei. n cadrul ochi, 11 - cis-

retinieneeste obligat s rodopsinei (tije) i iodopsin (conuri), de la reziduuri conservate lizin.

Ca lumina intra in ochi, de 11 - cis-retinieneeste izomerizai la toate "trans" form. All-"trans"

disociaz de retina de la opsin ntr-o serie de trepte numit foto-albire. Acest izomerizare induce

un semnal nervos de-a lungul nervului optic la centrul vizual al creierului. Dup separarea de la

opsin, toate-"trans"-retiniene este reciclat i convertit napoi la 11 - "cis", retina forma de o serie

de reactii enzimatice. n plus, unele din toate "trans", a retinei pot fi convertite la toate, "trans",

forma retinol si apoi transportate cu un interphotoreceptor-retinol de proteina de legare (IRBP),

la celulele epiteliale de pigment. Esterificarea n continuare n toate de esteri de "trans" retinil

permit stocarea de all-trans-retinol n celulele epiteliale de pigment s fie refolosite atunci cand

este nevoie.Etapa final este de conversie de 11 - cis-retinieneva rebind la opsin de a reforma

rodopsinei n retinei. Rodopsinei este necesar pentru a vedea n lumin sczut (de contrast),

precum i pentru vederea de noapte. Acesta este motivul pentru care o deficienta de vitamina Ava inhiba procesul de reformare a rodopsinei i conduce la una din primele simptome, orbire

noapte.
http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Haematopoiesis&usg=ALkJrhhZ7sNf05TWu2iSq6YYWYTBxrhTlAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Haematopoiesis&usg=ALkJrhhZ7sNf05TWu2iSq6YYWYTBxrhTlA


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Gene transcriere

Vitamina A, n forma de acid retinoic, joac unrol important n transcriere gena. Odat

ce retinol a fost preluat de ctre o celul, aceasta poate fi oxidat pentru a retinei (retinaldehyde),

prin dehidrogenazelor retinol i apoi retinaldehyde poate fi oxidat la acid retinoic dedehidrogenazelor retinaldehyde. De conversie de retinaldehyde la acid retinoic este un pas

ireversibil, ceea ce nseamn c producia de acid retinoic este strict reglementat, ca urmare a

activitii sale ca un ligand pentru receptorii nucleare.

Dermatologie

Vitamina A, i mai precis, acidul retinoic, pare a menine sntatea pielii normale prin

comutarea de pe gene si diferentierea keratinocitelor (celule imature ale pielii) in celule matureepidermice,mecanismele exacte spatele agenti farmacologici retinoid terapie n tratamentul

bolilor dermatologice sunt in curs de cercetare. Pentru tratamentul deacnee , de droguri retinoid

cel mai prescris este de 13-cis retinoic acid (isotretinoin ). Acesta reduce dimensiunea i

secreia glandelor sebacee. Dei este cunoscut faptul ca 40 mg de isotretinoin se va rupe pn la

echivalentul a 10 mg de ATRA - mecanismul de aciune al medicamentului (numele original

Accutane de brand), rmne necunoscut i este o chestiune de unele controverse.

Isotretinoin reduce numrul de bacterii n ambele conducte si suprafata pielii. Acest

lucru este considerat a fi un rezultat al reducerii n sebum, o sursa de substante nutritive pentru

bacterii. Isotretinoin reduce inflamatia prin inhibarea rspunsurilor chemotactici de monocite i

neutrofile. Izotretinoinul, de asemenea, a fost demonstrat de a iniia remodelare a glandelor

sebacee, determinnd schimbri n expresia genelor care induc selectivapoptoza . Isotretinoin

este unteratogen , cu un numr de potenial de efecte secundare. Prin urmare, utilizarea sa

necesit supraveghere medical.

Retiniana / retinol comparativ cu acid retinoic

Vitamina A obolani defavorizate pot fi pstraten stare bun de sntate, cu suplimente

deacid retinoic . Acest lucru inverseaz efectele de cretere piticirea de deficit de vitamina A,

precum i etapele timpurii alexeroftalmie . Cu toate acestea, astfel de obolani arat infertilitate
http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Acne&usg=ALkJrhjH7kjNpjkwdSGHWyHVVirAGEPFEghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Isotretinoin&usg=ALkJrhgbOX3lxSpaAiIWzmqnLSa0hLKowQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Apoptosis&usg=ALkJrhje9Y6MnjngzUG_BzrllT8k6eHvUAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Apoptosis&usg=ALkJrhje9Y6MnjngzUG_BzrllT8k6eHvUAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Teratogen&usg=ALkJrhilpdv8gqo_JAfrTDQagWdXch_GMwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinoic_acid&usg=ALkJrhhG2_mheQtw9uuNk0W524HcFGifGAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Xerophthalmia&usg=ALkJrhgkfoTEcEeHWykGxnowHekpTyhv4ghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Xerophthalmia&usg=ALkJrhgkfoTEcEeHWykGxnowHekpTyhv4ghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Xerophthalmia&usg=ALkJrhgkfoTEcEeHWykGxnowHekpTyhv4ghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinoic_acid&usg=ALkJrhhG2_mheQtw9uuNk0W524HcFGifGAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Teratogen&usg=ALkJrhilpdv8gqo_JAfrTDQagWdXch_GMwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Apoptosis&usg=ALkJrhje9Y6MnjngzUG_BzrllT8k6eHvUAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Isotretinoin&usg=ALkJrhgbOX3lxSpaAiIWzmqnLSa0hLKowQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Acne&usg=ALkJrhjH7kjNpjkwdSGHWyHVVirAGEPFEg


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(n att brbai, ct i femei), i continu degenerare a retinei, artnd c aceste funcii necesit

retinei sau retinol, care sunt intraconvertable, dar care nu pot fi recuperate de la acid retinoic

oxidat. Cerina de retinol pentru a salva reproducere in vitamina A obolani cu deficit de acum

este cunoscut a fi cauzat de o cerin pentru sinteza local de acid retinoic de retinol n testicul i

de embrioni.

Deficien

Deficit de vitamina A este estimat a afecta aproximativ o treime din copiii sub vrsta de

cinci ani n jurul lumii. Se estimeaz de a pretinde viaa de 670.000 copii sub cinci ani anual.

Aproximativ 250,000-500,000 copii n rile n curs de dezvoltare devin orb n fiecare an pentru

a cauza deficit de vitamina A, cu cea mai mare prevalen n Asia de Sud i Africa.

Deficit de vitamina A poate avea loc fie ca un primar sau un deficit secundar. Un primar

de vitamina A deficit apare n rndul copiilor i adulilor care nu consuma un aport adecvat de

provitamina A carotenoizi din fructe i legume sau de vitamina A semifabricate de la animale i

de produse lactate. Intarcare timpurie de la laptele matern poate crete, de asemenea, riscul de

deficit de vitamina A.

Un deficit de vitamina secundar este asociat cu sindrom de malabsorbie cronic de

lipide, productia de bila tulburri i de pres, i de expunerea cronic la oxidani, cum ar fi fumul

de tigara, i alcoolismul cronic. Vitamina A este o vitamin solubil n grsimi idepinde de

solubilizare micelar pentru dispersie n intestinul mic, ceea ce duce la utilizarea incorect de

vitamina A de la low-diete de grasimi. Deficitul de zinc poate afecta, de asemenea, absorbia,

transportul, metabolismul i de vitamina A., Deoarece este esenial pentru sinteza de vitamina A,

proteine de transport i ca cofactor n conversia de la retinol retiniene n populaiile subnutriti,

prize de comune mici de vitamina A si zinc, crete gradul de severitate al deficitului de vitamina

A i conduce semne fiziologice i simptome de deficit. Un studiu nBurkina Faso au aratatreducerea majora a morbiditatii malariei combinat cu vitamina A sizinc , n suplimentarea copiii

mici.

Datorita functiei unice de retina ca un cromofor vizual, una dintre cele mai vechi

manifestri specifice i dedeficit de vitamina A este cu probleme de vedere, n special n lumin
http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Burkina_Faso&usg=ALkJrhiu9JEVDz_eV5gmAjEpA3muZJLmDQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Burkina_Faso&usg=ALkJrhiu9JEVDz_eV5gmAjEpA3muZJLmDQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Zinc&usg=ALkJrhiAMe4uEGoQBFh3Pp4NbNftIrNgMghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Zinc&usg=ALkJrhiAMe4uEGoQBFh3Pp4NbNftIrNgMghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Burkina_Faso&usg=ALkJrhiu9JEVDz_eV5gmAjEpA3muZJLmDQ


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redus -orbirea de noapte . Deficit persistent d natere la o serie de schimbri, cea mai

devastatoare care apar n ochi. Unele alte modificri oculare sunt menionate caxeroftalmie . n

primul rnd exist uscaciune a conjunctivei (xeroza ), ca lacrimal normal i mucus-secretoare

epiteliului este nlocuit de un epiteliu keratinized. Aceasta este urmata de acumularea de resturi

de keratina din plci mici, opace (pete Bitot lui ) i, eventual, eroziuneade suprafata corneei

uniformizat, cu nmuiere i distrugerea corneei (keratomalacia ) i orbire totala. Alte modificri

includ afectat imunitate (risc crescut de infectii ale urechii, infecii ale tractului urinar, boala

meningococica), hiperkeratoza (noduli albe la foliculii de par),keratoza pilaris imetaplazie

scuamoasa a epiteliului mucoasei cailor respiratorii superioare i a vezicii urinare la un epiteliu

keratinized. Cu relaii la stomatologie, un deficit de vitamina A duce la smalt hipoplazie.

Vitamina alimentare adecvat, dar nu in exces A, este deosebit de important pentrufemeile gravide i care alpteaz, pentru dezvoltarea normal a ftului. Deficiene nu pot fi

compensate prinpostnatale suplimentarea. Excesul de vitamina A, care este cel mai frecvent cu

suplimente de ridicat de vitamina doze, poate provocamalformaii congenitalei, prin urmare,

nu trebuie s depeasc valorile zilnice recomandate.

Vitamina A inhibarea metabolice, ca urmare a consumului de alcool in timpul sarcinii

este mecanismul de elucidat pentru sindromul de alcool fetal i se caracterizeaz prin efecte

teratogene potrivesc cel mai bine de vitamina A deficit matern.

Suplimentarea cu vitamina A

Eforturile globale de sprijinire a guvernelor naionale, n abordarea deficit de vitamina A

sunt conduse de Alianta Globala pentru Vitamina A (Gava), care este un parteneriat informal

ntre A2Z,canadian Ageniei Internaionale pentru Dezvoltare ,Helen Keller International ,

Iniiativa de micronutrieni,UNICEF ,USAID , iBanca Mondial. Comun Gava activitate

este coordonat de ctre Iniiativa Micronutrienti.

n timp ce strategii includ aportul de vitamina A, printr-o combinaie a alptrii i aportul

dietetic, livrare pe cale oral de doze mari de suplimente n continuare strategia principal pentru

reducerea deficitului. O meta-analiz a 43 studii au aratat ca vitamina A suplimentarea de copii

sub cinci care sunt la risc de deficit reduce mortalitatea cu pn la 24%. Aproximativ 75% din
http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinol&usg=ALkJrhhWkTeb4cDfvbPFypoE4IE2tXvj3g#Night_visionhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Xerophthalmia&usg=ALkJrhgkfoTEcEeHWykGxnowHekpTyhv4ghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Xerophthalmia&usg=ALkJrhgkfoTEcEeHWykGxnowHekpTyhv4ghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Xerosis&usg=ALkJrhhW_WKhveF35qMSipfyGahsVvn06whttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Xerosis&usg=ALkJrhhW_WKhveF35qMSipfyGahsVvn06whttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Bitot%27s_spots&usg=ALkJrhhcBhO2sDmt0vnEScWitrBsOi51Nwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Bitot%27s_spots&usg=ALkJrhhcBhO2sDmt0vnEScWitrBsOi51Nwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Keratomalacia&usg=ALkJrhgx-gTcrZUecYBHgsWFtG5ZvsIGNghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Keratomalacia&usg=ALkJrhgx-gTcrZUecYBHgsWFtG5ZvsIGNghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Keratosis_pilaris&usg=ALkJrhj-XdbaAFhQ7rAXq2QZDT8biongwwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Squamous_metaplasia&usg=ALkJrhj3HTJS7ekZE1VGCcfzHRpH_3T6gwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Squamous_metaplasia&usg=ALkJrhj3HTJS7ekZE1VGCcfzHRpH_3T6gwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Squamous_metaplasia&usg=ALkJrhj3HTJS7ekZE1VGCcfzHRpH_3T6gwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Postnatal&usg=ALkJrhhhr4muSobDYOMly1J8h8BUJpTFRAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Birth_defects&usg=ALkJrhiEFWFAGlTgdww3IOMZKnbZzPiXFwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Birth_defects&usg=ALkJrhiEFWFAGlTgdww3IOMZKnbZzPiXFwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Birth_defects&usg=ALkJrhiEFWFAGlTgdww3IOMZKnbZzPiXFwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Canadian_International_Development_Agency&usg=ALkJrhhqKe0tFc9VqhHp6itiZ8Hf07_-hwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Canadian_International_Development_Agency&usg=ALkJrhhqKe0tFc9VqhHp6itiZ8Hf07_-hwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Canadian_International_Development_Agency&usg=ALkJrhhqKe0tFc9VqhHp6itiZ8Hf07_-hwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Helen_Keller_International&usg=ALkJrhj80Nlvt6wRLCslYM2UmK0lM4tLsAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Micronutrient_Initiative&usg=ALkJrhgtb6jkrJ0ALBRqWISp5p1imdzO-whttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Micronutrient_Initiative&usg=ALkJrhgtb6jkrJ0ALBRqWISp5p1imdzO-whttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/UNICEF&usg=ALkJrhgRtBMF6l7gamyJRl8jVRiAx4BNBAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/USAID&usg=ALkJrhhZOmvDjBbnoFqsOlYNY8wUf2y3Sghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/World_Bank&usg=ALkJrhiwLNgYWyUIPK_H3kuS_FJEti2Rxwhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/World_Bank&usg=ALkJr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vitamina A necesare pentru activitatea de suplimentarea de ctre rile n curs de dezvoltare este

furnizat de ctre Iniiativa de micronutrieni, cu sprijin de la Agenia Canadian pentru

Dezvoltare Internaional. Abordri de fortificare a alimentelor sunt din ce n ce mai realizabil,

dar nu poate asigura un nivel de acoperire nc.

Organizaia Mondial a Sntii estimeaz c Suplimentarea cu vitamina A a reuit s

evite 1,25 milioane de decese cauzate de deficit de vitamina A n 40 de ri din 1998. n 2008, sa

estimat c o investiie anual de 60 milioane de suplimente de vitamina A si zinc, combinate ar

genera beneficiile de mai mult de 1 miliard de USD pe an, cu fiecare dolar cheltuit de beneficii

de mai mult de US $ 17. Aceste intervenii combinate s-au clasat de Consensul de la Copenhaga

2008, ca de investiii din lume cel mai bun de dezvoltare.

Toxicitate

Deoarece vitamina A este solubila in grasimi, care dispune de orice excese luate n prin

diet este mult mai greu dect cu ap, solubile vitamine B si vitamina C, vitamina A de toxicitate

este posibil.

n general, toxicitatea acut apare la doze de 25.000UI /kg de greutate corporal, cu

toxicitate cronic apare la 4.000 UI / kg de greutate corporal pe zi timp de 6-15 luni.[38]Cu

toate acestea, toxice hepatice pot s apar la niveluri ct mai sczute 15.000 UI pe zi, la 1,4

milioane UI pe zi, cu o doz zilnic medie toxica de 120000 UI pe zi, n special cu consumul

excesiv de alcool. La persoanele cuinsuficien renal, 4000 UI poate provoca daune

substaniale. n plus, consumul excesiv de alcool poate crete toxicitatea. Copiii se pot atinge

niveluri toxice la 1.500 UI / kg de greutate corporal.

Un consum excesiv de vitamina poate duce la greata, iritabilitate,anorexie (apetitului

redus), vrsturi, vedere nceoat, dureri de cap, pierderea parului, dureri musculare si

abdominale i de slbiciune, somnolen, i alterarea statusului mental. n cazurile cronice,

caderea parului, piele uscat, uscarea mucoaselor, febra,insomnie , oboseala, pierderea in

greutate, fracturi osoase, anemie, i diaree pot fi deloc evident pe partea de sus a simptomelor

asociate cu o toxicitate mai puin grav. Unele dintre aceste simptome sunt, de asemenea,

comune pentru acnee tratament cuisotretinoin . Cronic doze mari de vitamina A, i, de
http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/International_unit&usg=ALkJrhhuvICOywthlGFwzS0QLdZK5w3rLAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/International_unit&usg=ALkJrhhuvICOywthlGFwzS0QLdZK5w3rLAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Kilogram&usg=ALkJrhh0mNZAwQ_M06E5EMdRkRIBclG5lghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-37http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-37http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-37http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Renal_failure&usg=ALkJrhgioivdv9vzrL_IKGeM1yLoBGqYOAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Renal_failure&usg=ALkJrhgioivdv9vzrL_IKGeM1yLoBGqYOAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Renal_failure&usg=ALkJrhgioivdv9vzrL_IKGeM1yLoBGqYOAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Anorexia_(symptom)&usg=ALkJrhiSdlc45O4_QONTe1hBUx1KjbMWlAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Insomnia&usg=ALkJrhgPfFX9cx9NxL3gjj6TrYU9l-X2rAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Insomnia&usg=ALkJrhgPfFX9cx9NxL3gjj6TrYU9l-X2rAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Isotretinoin&usg=ALkJrhgbOX3lxSpaAiIWzmqnLSa0hLKowQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Isotretinoin&usg=ALkJrhgbOX3lxSpaAiIWzmqnLSa0hLKowQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Insomnia&usg=ALkJrhgPfFX9cx9NxL3gjj6TrYU9l-X2rAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Anorexia_(symptom)&usg=ALkJrhiSdlc45O4_QONTe1hBUx1KjbMWlAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Renal_failure&usg=ALkJrhgioivdv9vzrL_IKGeM1yLoBGqYOAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-37http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Kilogram&usg=ALkJrhh0mNZAwQ_M06E5EMdRkRIBclG5lghttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/International_unit&usg=ALkJrhhuvICOywthlGFwzS0QLdZK5w3rLA


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asemenea, farmaceuticeretinoizi , cum ar fi13-cis de acid retinoic , poate produce sindromul

pseudotumor cerebri . Acest sindrom include dureri de cap, vedere nceoat i confuzie,

asociat cu creterea presiunii intracerebrale. Simptomele incep sa se rezolva atunci cand aportul

de substane ofensatoare este oprit.

Aportul cronic de 1500 RAE de vitamina A pot fi asociate cu fracturi de old i

osteoporozei, deoarece suprima cldirea osoas, stimulnd n acelai timp distrugerea osului.[43]

Acest lucru se poate datora faptului c un exces de vitamina A poate bloca exprimarea anumitor

proteine dependente de vitamina K pentru a reduce eficacitatea de vitamina D, dar nu a fost nc

dovedit. Un aport ridicat de vitamine a fost asociat cu fracturi spontane la animale. Studiile

efectuate pe culturi de celule s-au legat de resorbie osoas a crescut i a sczut formarea osoas,

cu prize mari. Aceast interaciune poate s apar, deoarece vitaminele A i D, pot concurapentru acelai receptor i apoi s interacioneze cu hormon paratiroidian, care reglementeaz de

calciu. ntr-adevr, un studiu de Forsmo et al.arat o corelaie ntre densitatea mineral osoas

sczut i de aportul prea mare de vitamina A.

Efectele toxice ale vitaminei A au fost dovedit a afecta n mod semnificativ n curs de

dezvoltare fetusi. Dozele terapeutice utilizate pentru tratamentul acneei s-au dovedit a perturba

activitatea celulelor neuronale cefalice. Fatul este deosebit de sensibil la vitamina A de toxicitate

n timpul perioadei de organogeneza. Aceste toxice avea loc doar cu semifabricate (retinoizi),vitamina A. (cum ar fi de la ficat) Formularele de carotenoide (cum ar fi beta-caroten ca n

morcovi), nu d astfel de simptome, cu excepia cazului n suplimente i alcoolism chronoic, dar

aportul alimentar excesiv de beta-caroten poate duce lacarotenodermia , care provoac

modificri de culoare portocaliu-galben a pielii.

Fumatorii si consumatorii de alcool cronice au fost observate de a avea risc crescut de

mortalitate din cauza cancerului pulmonar, cancerul esofagian, cancerul gastro-intestinale si a

cancerului de colon. hepatic (ficat), a prejudiciului a fost gasit in studiile umane i animale, n

cazul n care consumul de alcool este asociat cu doze mari de vitamina A i beta-caroten

suplimentarea.
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Cercetatorii au reusit sa creeze solubile n ap forme de vitamina A, care au crezut ar

putea reduce potentialul de toxicitate. Cu toate acestea, un studiu din 2003 a constatat n ap

solubil vitamina A. a fost de aproximativ 10 ori mai toxic ca vitamina solubila in grasimi Un

studiu din 2006 a constatat copii de ap-solubil vitamina A si D, care sunt de obicei solubila in

grasimi, sufera de astm de dou ori la fel de mult ca un grup de control completat cu vitamine

solubile in grasimi.[51]

Vitamina A i derivaii si, n uz medical

Retinil palmitat a fost folosit in creme de piele, n cazul n care este defalcate la retinol si

aparent metabolizat la acid retinoic, care are o activitate puternic biologice, aa cum este descris

mai sus.

Celeretinoizi , (de exemplu,acidul 13-cis-retinoic ), constituie o clasa de compusi

chimici chimic legate de acid retinoic, i sunt folosite n medicin pentru a modula functii gene,

n loc de acest compus. Cum ar fi acidul retinoic, compuii aferente nu au vitamina A plin de

activitate, dar nu au efecte puternice asupra expresiei genelor si diferentierea celulelor epiteliale.

Farmaceutic folosesc doze de mega natural derivai de acid retinoic sunt utilizate n

prezent pentru cancer, HIV, i n scopuri dermatologice. La doze mari, efectele secundare sunt

similare cu vitamina A de toxicitate. Reacii adverse severe legate de vitamina A de toxicitate,

precum i o gam mic optim de utilizare sunt obstacole-cheie n dezvoltarea de vitamina A-

derivate farmaceutic pentru uz terapeutic.

Cromatografia de lichide

Termenul de cromatografie de lichide este utilizat pentru a denumi o gama extinsa de

sisteme cromatografice care au n comun faptul ca utilizeaza o faza mobila lichida.

Comparativ cu cromatografia de gaze, cea de lichide are avantajul ca permite si

analizarea probelor greu volatile sau instabile termic, iar faptul ca si faza mobila participa la

separare ofera posibilitati suplimentare pentru realizarea unor separari eficiente.
http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-pmid17157660-50http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-pmid17157660-50http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-pmid17157660-50http://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinyl_palmitate&usg=ALkJrhi4FXIo_Dnqkm3YEn_ENijyf1I_zAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinoid&usg=ALkJrhgy4ZDMAoTdoi6mYUGuP8ZH3zwaeQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/13-cis-retinoic_acid&usg=ALkJrhiSL7-wSZ7A-Hys5-kMhwnhnxpJ5Ahttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/13-cis-retinoic_acid&usg=ALkJrhiSL7-wSZ7A-Hys5-kMhwnhnxpJ5Ahttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinoid&usg=ALkJrhgy4ZDMAoTdoi6mYUGuP8ZH3zwaeQhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Retinyl_palmitate&usg=ALkJrhi4FXIo_Dnqkm3YEn_ENijyf1I_zAhttp://translate.googleusercontent.com/translate_c?hl=ro&langpair=en%7Cro&rurl=translate.google.ro&u=http://en.wikipedia.org/wiki/Vitamin_A&usg=ALkJrhjlA-ta3u6JhIkZ8sfl_8JSYn6_ZQ#cite_note-pmid17157660-50


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Cromatografia de lichide clasica a fost caracterizata de utilizarea unor coloane cu

diametre mari, umplute cu particule de faza stationara de o granulatie fina si prin care faza

mobila trecea sub influenta fortei gravitationale. Aceste sisteme, care se mai folosesc azi n

separarile cromatografice lichid-solid, au permis realizarea separarii unor amestecuri complexe

de substante n conditii foarte bune, nsa viteza de separare este mica iar analiza suplimentara a

compusilor separati prin metode spectroscopice este mai dificila. Aparitia cromatografiei de

lichide de nalta performanta (HPLC) a permis eliminarea acestor deficiente si chiar impunerea

cromatografiei de lichide ca o metoda mai performanta de analiza dect cromatografia de gaze.

Principalele avantaje ale cromatografiei de lichide de nalta performanta sunt:

- Capacitate de separare ridicata

- Viteza ridicata a separarii

- Posibilitatea monitorizarii continue a efluentului coloanei

- Realizarea unor analize repetate si reproductibile utiliznd aceeasi coloana

- Automatizarea procedurii analitice si a prelucrarii datelor

Primul cromatograf de lichide modern a fost construit de Csaba Horvth la Universitateadin Yale n 1964 si a tehnica fost denumita cromatografie de lichide de nalta presiune (HPLC).

n continuare, termenul care s-a impus a fost cel de cromatografie de lichide de nalta

performanta. Prima separare realizata de grupul lui Horvth a fost cea a unor componente ale

acizilor nucleici. Dezvoltarea extraordinara a acestei tehnici n ultimii zeci de ani se datoreste n

mare masura faptului ca a permis analiza unor compusi care puteau fi separati foarte greu pe alte

cai, de exemplu a biomoleculelor.

Principalele tipuri de cromatografie de lichide sunt:

- cromatografia de adsorbtie lichid-solid (LSC)

- cromatografia de repartitie lichid-lichid (LLC)


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- cromatografia ionica (IC)

- cromatografia prin excluziune (SEC)

Factorii care influenteaza disponibilitatea fazei stationare

Asa cum rezulta din ecuatia volumului de retentie, nu numai taria interactiunii dintre

solut si faza stationara va fi cea care determina retentia solutului ci si volumul fazei stationare

prezente n sistem si accesibile solutului. Volumul fazei stationare cu care componentele

amestecului de analizat pot interactiona depinde de starea fizica a fazei stationare si a suportului.

Daca faza stationara este un solid poros si dimensiunile porilor suportului sunt comparabile cu

diametrele moleculare ale componentelor de separat, atunci faza stationara va fi selectiva pentru

marimea moleculelor acestora. Moleculele anumitor soluti vor putea patrunde n interiorulporilor si vor interactiona cu mai multa faza stationara dect alte molecule mai mari care vor fi

partial excluse de la aceste interactiuni. Asadar, separarea va fi controlata de fenomenul de

excluziune bazat pe marimea moleculelor si de aceea se numeste cromatografie de excluziune.

Daca faza stationara va fi chirala, cantitatea de faza stationara disponibila pentru a interactiona

cu solutul va fi doar aceea care din punct de vedere steric se potriveste cu orientarea spatiala a

moleculei de solut. Acest tip de cromatografie se numeste cromatografie de lichide chirala.

Trebuie mentionat ca n functie de natura fazei stationare ambele aceste tipuri, cromatografia deexcluziune sau cromatografia chirala, pot sa se ncadreze fie n categoria cromatografiei lichid-

lichid fie n a celei de tip lichid-solid.

Eficienta de separare a coloanei cromatografice

n timpul deplasarii prin coloana cromatografica nu este suficient ca benzile de elutie ale

celor doi soluti sa migreze diferentiat, ci este necesar ca ele sa fie destul de nguste pentru ca sa

se separe ct mai complet una de alta. Parametrul de eficienta care ne arata posibilitatea separarii

a doi compusi pe baza selectivitatii termodinamice este coeficientul de separare , definit pe baza

raportului factorilor de capacitate a celor doi soluti.


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Se observa ca coeficientul de separare coreleaza interactiunile din faza stationara si cele

din faza mobila.

Asadar n cromatografia de lichide, coeficientul de separare poate fi optimizat prin doua

modalitati:

- alegerea corespunzatoare a fazei stationare;

- alegerea corespunzatoare a fazei mobile.

Toti factorii care modifica interactiunile moleculare sau intensitatea acestora, att n faza

mobila ct si n sau faza stationara vor determina n acelasi timp si modificarea selectivitatii.

n cromatografia de lichide, faza stationara (indiferent ca este polara sau nepolara) va

adsorbi ntotdeauna n mod preferential o anumita componenta a eluentului, iar grosimea

stratului de adsorbtie (df)depinde de natura fazei stationare si a solventului adsorbit (Figura 1)Cu

ct ne ndepartam de suprafata, cu att scade taria legaturii acestei adsorbtii si este discutabil

unde trebuie plasata delimitarea dintre faza mobila adsorbita si cea neadsorbita. Daca se modifica

compozitia fazei mobile acest lucru determina automat si schimbarea compozitiei stratului de

faza mobila adsorbita la suprafata fazei stationare, iar drept consecinta modificarea interctiunilor

dintre solut si cele doua faze.


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Figura 1. Formarea stratului de faza mobila adsorbita pe suprafata fazei stationare

Analiza calitativa n cromatografia de lichide

Primul parametru care a fost utilizat pentru identificare n cromatografia de lichide a fostvolumul de retentie ajustat Vr. Exista nsa o problema majora privind utilizarea acestui

parametru, aceea legata de determinarea volumului mort. Volumul de retentie ajustat este

diferenta dintre volumul de retentie si volumul mort, nsa volumul mort (V M) ar trebui sa fie

doar volumul fazei mobile din coloana si nu volumul total de lichid care se gaseste ntre injector

si detector. Volumul mort total (VMt) va include si volumele aferente injectorului, tubulaturii de

conectare ntre injector, detector si coloana si celulei de masura. El se poate determinat doar

utiliznd un solut care nu se adsoarbe pe faza stationara si care are aceeasi marime moleculara cu

cea a solutului analizat pentru a avea aceleasi interactiuni de excluziune. Daca nsa volumul de

retentie ajustat este mult mai mare dect volumul mort total, atunci orice solut care nu se

adsoarbe poate fi utilizat pentru determinarea volumului mort si n acest caz volumul de retentie

ajustat poate fi utilizat drept parametru calitativ. Aceasta utilizare este nsa limitata de

dependenta volumului de retentie ajustat de conditiile de analiza, mai ales de lungimea coloanei

si debitul fazei mobile.

Tehnici ale cromatografiei de lichide

1. Cromatografia de adsorbtie lichid-solid

Cromatografia lichid-solid (LSC), numita si cromatografie de adsorbtie, utilizeaza o faza

mobila lichida si o faza stationara solida formata dintr-o pulbere poroasa avnd capacitate mare

de adsorbtie si o suprafata specifica ce variaza ntr-un domeniu foarte larg, ntre 50-1000 m2/g.

Acest tip de cromatografie se bazeaza pe interactiunea moleculelor solutului cu centrii activi

aflati pe suprafata unui adsorbent solid care reprezinta faza stationara. Adsorbentul se poate gasi

fie ntr-o coloana (n cazul cromatografiei pe coloana) fie pe suprafata unei placi (n cazul

cromatografiei n strat subtire). Granulatia umpluturii variaza pe un domeniu larg, de la 5 m n

cazul celor folositi n HPLC si pna la mai mult de 100 m n cazul celor folositi n

cromatografia pe coloane clasice.


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Cromatografia lichid-solid poate fi utilizata cu rezultate bune att pentru separarea

compusilor polari ct si a celor nepolari si este folosita cu precadere n separarile cantitative ale

amestecurilor de substante organice, atunci cnd aceste amestecuri nu sunt foarte complexe. n

general, compusii care se pot separa cel mai bine prin tehnica LSC sunt cei care au caracter

neionic si sunt solubili n solventi organici. Compusii neionici solubili n apa se separa mai bine

prin cromatografie de lichide pe faza inversa sau cromatografie cu faze chimic legate.

Din punct de vedere istoric, a fost prima tehnica cromatografica utilizata (vet).

Faze mobile utilizate n cromatografia lichid-solid

n cromatografia LSC se utilizeaza un mare numar de faze mobile lichide, ct si

amestecuri ale acestora de compozitie fixa sau compozitie variabila n timp. n crom

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