Fat Soluble Vitamins Flashcards
What are the fat soluble vitamins?
A,D,E,K
What do fat soluble vitamins need for absorption?
Bile and fats (emulsifiers)
What is an emulsifier?
Consists of a water loving hydrophilic head and an oil loving hydrophobic tail. The hydrophilic head is directed to the aqueous phase while the hydrophobic tail is directed to oil phase.
Where are excess vitamins stored?
Liver and adipose tissue
Digestion and absorption of fat soluble vitamins
1) Bound to proteins as we eat them.
2) Once in stomach, they are degraded into small peptides releasing vitamins.
3) Form micelles with bile salts allowing them to passively transport into intestinal enterocytes.
4) They are packaged into chylomicrons and released into lymphatic system.
5) Travel up the thoracic duct and enter left subclavian vein to enter circulation.
How do we obtain Vitamin A?
Retinyl esters from animal food and beta carotene from plant food. Retinal esters are converted into Retinol while beta carotene is converted into Retinal. Retinal is converted into Retinoic Acid
What is retinol important for?
Supports reproduction.
What is Retinal important for?
Participates in vision.
What is retinoic acid important for?
regulates growth
Is the conversion of Retinol into Retinal reversible?
Yes they can interconvert.
Is the conversion of Retinal into Retinoic Acid reversible?
No.
Liver is rich in Vitamin A (remember polar bear story). What form of vitamin A?
Retinyl esters
What vegetables are best for vitamin A and in what form?
Sweet potatoes and carrots. Vitamin A in form of Beta Carotene.
Biochemically, what is the difference between retinol, retinal, retinoic acid, and beta-carotene?
Retinol has a hydroxyl group, Retinal has an aldehyde, retinoic acid has a carboxyl group, and Beta carotene is a dimer of two retinal molecules.
What is the form of vitamin A that is circulating within chylomicrons in the plasma?
Retinol Ester
Where is retinol stored?
Retinol is stored in the stelatte cells.
Functions of Vitamin A
Vision Maintenance of cornea, epithelial cells, mucous membranes, skin Bone and tooth growth. Reproduction Immunity
Function of beta-carotene
Antioxidant
What happens to the epithelia in absence of vitamin A?
Goblet cells cannot function properly leading to flattened, abnormal epithelial cells with very little mucous.
What is the pharmacological use of retinoic acid?
Treatment of acute promyelocytic anemia
All Trans Retinoic acid (Retin-A) is also called? What is its use?
Tretionin, it is used as a topical treatment for acne, aging, dark pigments
Pharmacological use of 12-cis retinoic acid?
Isotretionin, (Accutane) and is used as oral treatment for cystic acne. Also it is a teratogen so it requires use of effective contraceptives.
Why is vitamin D important in vision?
Cells of retina, rods, contain pigment molecules called rhodopsin. It is composed of a protein called opsin bonded to a molecule of retinal.
Mechanism of retinal in eye
As light interacts with rhodopsin, retinal changes from cis to trans and it is released from opsin. The change allows opsin to initiate signal transduction cascade to nerve cells that communicate with the brain’s visual center. THIS IS IMPORTANT FOR NIGHT VISION.
What is 1’ deficiency of hypovitaminosis A vs. 2’ deficiency?
Primary deficiency is inadequate intake. Secondly deficiency is poor absorption of fats and can result from cystic fibrosis, crown’s disease, liver disease, excessive alcohol intake.
Symptoms of hypovitaminosis A?
Night blindness Blindness (xerophthalmia) Corneal drying (xerosis) triangular gray spots on eye (bitot spots) Softening of the cornea (keratomalacia) Dry skin due to hyperkeratosis impaired immunity
What happens to babies if moms use lots of accutane treatment during pregnancy?
Birth defects such as cranofacial malformation and malformation of CNS, Thymus, and heart
What is the other name of vitamin D?
Calciferol
What are good food sources of vitamin D?
Fish, fortified milk and mushrooms
Factors that contribute to deficiency?
Dark skin, no sun exposure, use of non fortified milk, vegan diet
What does vitamin D deficiency cause in infants and adults
Rickets in infants and osteomalacia in adults
How else can osteomalacia develop?
Long term anticonvulsants such as phenobarbital and phenytoin can cause increased breakdown of vitamin D in liver. And also in chronic kidney disease.
How does Vitamin D toxicity occur?
Occurs with supplementation and causes calcification of soft tissue.
What is the other name for vitamin E?
Tocopherol
Which molecule has vitamin E activity?
d-isomer of alpha tocopherol
How can d-isomer of alpha tocopherol be destroyed?
Oxygen or frying
What are good sources of vitamin E?
nuts and oil
Functions of vitamin E
Most effective lipid soluble antioxidant. Prevents platelet aggregation and monocyte adhesion. Assists in maintenance of fertility.
What does vitamin E depend on for activity
It depends on vitamin C
Vitamin E deficiency
Rare but can happen in premature babies. Causes erythrocyte hemolysis causing hemolytic anemia. We give premature babies vitamin E.
What is the animal form of vitamin K
menaquinone, made by gut bacteria and can be obtained from fish oil and meats.
What is the plant form of vitamin K
phylloquinone, can be obtained from green leafy vegetables, broccoli, peas and green beans.
Function of vitamin K
Required cofactor for post translational modification of glutamate to gamma-carboxyglutamate (GIa). Plays role in coagulation
What enzyme catalyzes glutamate to GIa reaction?
Gamma-glutamyl carboxylase
What can cause deficiency of vitamin K?
Use of antibiotics or malabsorption
Why do newborns have vitamin K deficiency and what can be done?
Due to lack of gut bacteria and we can give bolus of vitamin K injections shortly after birth.
What can cause toxicity of vitamin K?
Patients taking warfarin.
