Lecture 23: Fat-Soluble Vitamins Flashcards
Which two fat soluble vitamins are synthesized endogenously?
Vit D/K
Which two fat soluble vitamins are metabolized?
D/A
Provitamin A is a part of ___ family while Vit A is a part of ___ family
Carotenoids; Retinoids
B-carotene can convert to ___, which can convert to ___ , which can produce ____
retinal <—-> retinol
retinoic acid
11-cis retinal
What form of Vit A treats psoriasis and promyelocytic leukemia?
Trans retinoic acid
Which form of Vit A treats severe acne?
13-cis retinoic acid
What Vit A can you get from animal tissue vs. plants?
animal: retinyl esters; retinol
plants: b-carotene
Retinyl esters are broken down into ___ and ___ in the intestinal lumen
Fatty acids and retinol
In the intestine cells, retinol is re-esterified and incorporated into _____, which can be transported to liver/adipse
chylomicrons
How is Vit A stored? Where is it stored?
Retinyl Esters
-liver
-adipose
The liver can store 8-6 mths of Vit A with the help of a retinol binding protein known as _____
Transthyretin
Rhodopsin is typically bound to inactive 11 cis-retinol and opsin. When light strike, __ breaks down and actives ___ and ___
rhodopsin ; trans-retinal and cGMP
Conformational change in opsin generated nerve ___
impulse
All trans retinal can be use to make more _____
11-cis retinal
In target tissues, retinol is oxidized to ______
retinoic acid
What complex can active/inhibit genes?
Retinoic acid-receptor complex
What form of Vit A functions in gene regulation?
All-trans retinoic acid
If epithelial cells have a good supply of retinal, it is converted to retinoic acid and no ___ is made
Keratin
____ _____ suppresses synthesis of keratin by binding to nuclear receptor
Retinoic Acid
Why do epidermal epithelial cells usually undergo terminal keritinization?
Not vascularized, no retinal, therefore: no retinoic synthesis
______ cells secrete mucus to keep moist. They do not usually keratinize.
Internal Epithelial Cells
How does Vit A decrease cancer risk?
Acts as an anti-oxidant substance
Hypervitaminosis of Vit A?
Hypovitaminosis of Vit A?
Hypervitaminosis: Teratogen
Hypovitaminosis: Severe xeropthalmia
Mild hypovitaminosis of Vit A
-night blindness
-anemia
-follicular hyperkeratosis
What 4 populations require additional Vit A?
1) premature infants
2) people w/ fat malabsorption/deficiency/pancreatic insufficiency
3) hepatobil tree disease
4) intestinal mucosa dysfunction
How can ergocalciferol (Vit D2) can be obtained?
Dairy
How can cholecalciferol (Vit D3) be generated?
UV light converted 7-dehydrocholesterol to Vit D3
For Vit D3 to be converted to its active form two processes must occur, one in the ___ and the other in the ___.
Liver; kidney
CYP2R1 in the liver creates ____
CYP27B1 produces ____, active form of Vit D, which inhibits further Vit D3 production
25-OH-cholecalciferol
1,25-diOH-cholecalciferol
Ergosterol + UV = ?
Ergocalciferol
How does Vitamin D/PTH inhibit calcium excretion from kidney?
Stimulates calcium reabsorption
Under what two conditions do you require more Vit D?
1) Fat malabsorption disorder
2) Use of corticosteroids/anticonvulsants
Hyper vs. Hypovitaminosis of Vit D?
Hypervitaminosis: growth retardation, calcify soft tissues, permanent kidney damage
Hypovitaminosis: rickets; osteomalacia
What happens when serum calcium levels are low?
Increase PTH, calcitrol, more calcium is reabsorbed from bone, more renal absorption of calcium, more calcium absorbed from intestine
Three functions of 1,25-dihydroxycholecalciferol (calcitrol)?
1) Induces synthesis of calbindin
2) Works with PTH to ensure bone reabsorption
3) Works with PTH to inhibit calcium excretion from kidney
In the intestine, Vit D induces synthesis of ___, which absorbs dietary calcium
calbindin
What fat-soluble vitamin has no toxicity associated with excess of it?
Vit K
Under what two conditions would a patient require more Vit K than usual?
1) Broad spectrum abx’s
2) Counteract OD of coumadin
Why do newborns often get prophylactic dose of Vit K?
They have sterile GI and low liver stores of Vit K. Also, breast milk is low in Vit K
Hypovitaminosis of Vit K?
Hemorrhage
What can pre-dispose a patient to hypovitaminosis of Vit K?
1) Total parentral nutrition
2) Liver Dysfunction
3) Maladaption Syndrome
Role of Vit K?
Co-factor in gamma-carboxylation of glutamine residues in:
-Coag factors
-Bone proteins
Phylloquinone = Vit
K
While various forms of vit E are absorbed, which is the only one to be retained?
alpha-tocopherol
Main function of Vit E?
Anti-oxidant
Increase fragility of RBC membrane is associated with hypovitaminosis of what fat-soluble vitamin
Vit E
Epithelial cells will not make ___ as long as they are supplied with retinal to make retinoic acid
keratin
Three functions of Vit A?
Vision
Gene regulation
Anti-oxidant
______ is a component of the visual pigment rhodopsin
11 cis-retinal
Cholecalciferol is converted to the
active form by two hydroxylations - the first is in the ____ while the second is in the ____
Liver; kidney (yields active form of vit D: 1,25 diOH cholecalciferol)
