sources what does it do main mechanisms deficiency toxicity symptoms absorption things that stand out when treating a patient VITMAN A a general term given to all compounds that possess the biological activity of all trans retinol Retinoids aka preformed vitamin A what you get that s in your animal products retinal retinol retinoic acid Carotenoids aka provitamin A can be converted to retinol colorful pigments yellow orange that are in your food that can be converted to retinol carotene carotene and cryptoxanthin Carotenoids More than 600 of them Others lycopene canthaxanthin lutein Zeaxanthin Pro vitamin A Carotenoids Can be converted to retinol carotene cryptoxanthin carotene I II Sources A Retinoids B Carotenoids RDA Males 900 g d RAE Females 700 g d RAE encompasses all forms RAE retinol activity equivalents Foods of animal origin liver cheese fish liver oils of fish Yellow orange and red fruits and vegetables papayas carrots tomatoes squash cantaloupe broccoli spinach beets vegetarians can get all vitamin A they need from carotenoids C Supplements don t typically find a vitamin A pill because it can lead to a toxicity All trans retinyl acetate all trans retinyl palmitate III Retinol Activity Equivalents RAE A Foods 1 RAE 1 g retinol animal products 12 g carotene carrots 24 g carotene carotene is more active than other carotenoids but conversion is fairly poor B Supplements 1 RAE 1 g retinol IV Forms A Retinoids Retinol alcohol group Retinal aldehyde group Retinoic Acid carboxylic acid Retinyl Esters retinyl palmitate 16 C fatty acid ester group All of these can convert fairly easily between each other V VI A Carotenoids provitamin A B Carotenoids no provitamin A activity but do have antioxidant activity Over 600 60 can be converted to retinol carotene long unsaturated tail carotene cryptoxanthin Lutein Lycopene red coloration Zeaxanthin orange coloration Canthaxanthin red orange coloration VII Digestion and Absorption A Preformed vitamin A 70 90 bioavailable Micelle formation B Carotenoids 5 60 Small amounts of carotene passes through membrane unchanged Micelle formation Vitamin E large doses may inhibit absorption and the conversion of carotene C Factors influencing to retinol VIII Metabolism Vitamin A is kind of like a mineral because it is always bound to something A CRBP cellular retinol binding protein CRBP I liver kidney CRBP II intestine CRBP III liver kidney skeletal muscle heart CRBP IV heart kidney colon LRAT lecithin retinol acyl transferase B Esterifies a FA onto a CRBP bound retinol to form CRBP retinylpalmitate Figure on Blackboard Enterocyte CRBP carries out several conversions Transport 2 ways Bound to albumin or chylomicron Chylomicron remnant drops off retinyl esters off at tissues then comes into the liver Liver CRBP retinol main factor where we decide how we are going to use it can convert to retinoic acid and go into the nucleus to serve in functions like gene expression cell growth or cell differentiation to retinyl esters for storage or send to eye as Holo RBP for the visual cycle Eye cells for transport to eye need Holo RBP TTR IX Transport A Chylomicrons enterocyte to tissues B Lipoproteins liver to other tissues Predominately carotenoids C Holo RBP TTR complex Responsible for transport retinol from liver to tissues Retinol binds to RBP retinol binding protein In plasma we call this Holo RBP binds to transthyretin TTR Once in plasma Holo RBP TTR complex carried on protein T4 and carried to eye X Storage A As retinyl esters B Liver stellate cells are the predominate storage Once these are full you start to see retinyl esters in blood which means you have a toxicity of Vitamin A XI Functions A Retinol 1 Visual cycle a Eyes contain rods for black and white and cones for color 1 Rods dark adapted vision retinol only works within rods 2 Cones color b Rods retinol only works within rods 1 Rhodopsin main components of rods i 11 cis retinal when light hits the eye cis converts to trans which is how we see ii Opsin iii These two are the main components of rhodopsin 2 Light i Changes 11 cis retinal to all trans retinal ii This change activates Opsin Binds to a G protein GTP Sends visual signal to brain 3 11 cis retinal must be regenerated to send next visual signal to 4 Night blindness happens when we get older and with vitamin A brain deficiency i Delayed recovery of vision in dark after exposure to a flash of light ii Vitamin A status directly related 1 Retinoic acid differentiates keratinizing cells into mucus secreting cells such as eyes nose and other openings of your body multi pluri potent cell where if you have vitamin A you can make a mucus producing cell but if you don t it will make a keratinizing cell i Does this through gene expression mucus producing gene is turned on when there is Vitamin A to bind to DNA 2 Cellular differentiation a Keratinocytes 3 Gene expression a Retinoic acid binds to RAR retinoic acid receptors on DNA to regulate transcription described above also 4 Growth a Remodeling of epiphyseal cartilage b See stunted growth with insufficient vitamin A 1 Antioxidants eye health heart disease cell growth cellular differentiation and B Carotenoids proliferation a Macular degeneration oxidative damage to macula of eye b Inhibit oxidation of LDL s XII Assessment A Serum retinol reflects stores only when liver is depleted B Serum retinyl esters reflects toxicity levels in liver there should not be any retinyl esters in blood unless toxicity C RDR Relative dose response serum test before and after a dose of retinol D CIC conjunctival impression cytology test eye for goblet cells mucus producing cells in the eye XIII Deficiency A Signs and symptoms Night blindness Xerophthalmia basically dry eyes 1 Conjunctival and corneal xerosis 2 Bitot s spots keratinizing cells on cornea of eye Anorexia Stunted growth Increased susceptibility to infections Keratinization of mucosal cells with decreased differentiation follicular hyperkeratinosis rough goose bumpy skin B At risk Fat malabsorption Alcoholism retinal Dehydrogenase XIV Toxicity A Signs and symptoms Liver damage Retinol 1 2 Dry skin alopecia 3 Pharmacological doses acne medicine a Teratogenic birth defects not bound to RBP b Accutane pill for acne that is very effective for acne but causes birth defects Carotenoids 1 Carotenodermia or hypercarotenosis with C for coloration not K a Over ingestion of carrot and tomato tanning pills b Yellow jaundice like coloration around palms of hands and
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