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Nutritional Physiology > Fat Soluble Vitamins > Flashcards

Fat Soluble Vitamins Flashcards

1
Q

Vitamin A

What are the two forms of vitamin A

A

Preformed Vitamin A - active form in the body
* retinoids (retinal, retinal, retinoic acid)
* found in animal products

Provitamin A
* Carotenoids (beta-carotene, alpha carotene, lutein, lycopene, zeaxanthin, canthaxanthin)
* must be converted to retinoid form
* Found in plants

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2
Q

Vitamin A

Transport of Vitamin A

A

Transported via chylomicrons or VLDL to the liver
* Transported from the liver as retinol via retinol-binding protein (RBP) to target tissue

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3
Q

Vitamin A

Functions of Vitamin A

A
  1. Retinol is needed for reproduction (sperm production and foetal development)
  2. Retinoic acid supports growth and cell maturation, bone formation and gene expression
  3. Retinal is needed for night and colour vision

Retinol to Retinal -> Retinoic acid

Essential for vision, healthy epithelial tissues and growth

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4
Q

Vitamin A

The Visual Cycle - Cones

A
  • responsible for vision under bright lights
  • translate objects to colour vision
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5
Q

Vitamin A

The Visual Cycle - Rods

A
  • Responsible for vision in dim lights
  • Translates objects to black and white vision
  • Contains a pigment – rhodopsin (protein opsin bound to retinal)
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6
Q

Vitamin A

Cell Health and Maintenance

A
  • Epithelial cells line the outside (skin) and external passages (mucus forming cells) within the body
  • Retinoic acid influences how epithelial cells differentiate and mature
  • Without vitamin A, cells will deteriorate
  • Leads to xerophthalmia (major cause of blindness) and follicular hyperkeratosis (skin disorder)
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7
Q

Vitamin A

Deficiency of Vitamin A

A
  1. Night blindness (inadequate cis-retinal)
  2. Decreased mucus production
  3. Bacterial invasion in the eye

Xerophthalmia:
Conjunctival xerosis (dryness) -> Bitot’s spots (plaque formation) -> Irreversible blindness

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8
Q

Vitamin A

Toxicity of Vitamin A - Chronic

A
  • Bone/muscle pain, loss of appetite, skin disorders, headache, dry skin, hair loss, increased liver size, vomiting
  • Increased activity of osteoclasts causes weakened bones and contributes to osteoporosis and fractures
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9
Q

Vitamin A

Toxicity of Vitamin A - Teratogenic (affects of foetal development)

A

Teratogenic (affects foetal development)
* Can produce physical defects on developing foetus e.g. spontaneous abortion, birth defects

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10
Q

Vitamin A

Hypercarotenaemia

A
  • High amounts of carotenoids in the bloodstream turns skin a yellow-orange colour
  • Excessive consumption of carrots/squash/betacarotene supplements
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11
Q

Vitamin A

Food Sources of Vitamin A

A

Preformed - retinoids
* Liver, fish oils, fortified milk, eggs
* Contributes to half of the average vitamin A intake

Proformed - Beta carotene and carotenoids
* Dark-green leafy vegetables, yellow-orange vegetables/fruits

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12
Q

Vitamin D

What are the two sources of Vitamin D

A
  1. Dietary
    * Vitamin D2 from plants
    * Vitamin D3 from animals
  2. Endogenous
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13
Q

Vitamin D metabolism

7-dehydrocholesterol

A

Precursor (in the skin) that converts to vitamin D3

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14
Q

Vitamin D metabolism

Cholecalciferol

A

Vitamin D from sunlight trigger the converison of a cholesterol present on our skin > convets to cholecalciferol (D3) in blood

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15
Q

Vitamin D metabolism

Calcidiol

A

In our liver, an enzyme will hydroxylate the cholecalciferol molecule turning it into calcidiol

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16
Q

Vitamin D metabolism

Calcitriol

A
  • is the active form of vitamin D
    Calcidiol will be further activated in the kideny through hydroxylation = Calcitriol (active form of Vitamin D)
17
Q

Vitamin D metabolism

PTH (parathyroid hormone)

A

When blood calcium and phosphate levels are low the
release of enzymes (1-α hydroxylase) will be released
* This stimulates the activation of Vitamin D

PTH (parathyroid hormone) will trigger the 1-α hydroxylase

  • PTH also regulates calcium
  • Love blood valcium = increases PTH = increases osteoclast activity

Osteoclasts: promote bone demineralisation

18
Q

Vitamin D

Function of Vitamin D

A

Vitamin D is a hormone – a compound manufactured by one part of the body that causes another part to respond
* Resulting in the body producing the minerals needed for bone growth and maintenance
* Regulates synthesis of bone proteins (Vitamin K helps synthesise this protein)

19
Q

Vitamin D

Vitamin D deficiency - Rickets

A

Rickets: Low vitamin D in children (requires both lack of exposure to sunlight and a poor diet)
* decreased calcification of growing ends of bones (epiphyses)
* Bones bow under pressure
* Seen in cystic fibrosis (fat malabsorption)

20
Q

Vitamin D

Vitamin D deficiency - Osteomalacia

A

Osteomalacia: (soft bone) adult form of rickets
* Due to dietary vitamin D deficiency, lack of sunlight or to extensive liver or kidney damage
* Less obvious symptoms compared to children

21
Q

Vitamin D

Vitamin D deficiency - osteoporosis

A

Osteoporosis = low bone density (higher risk of fracture)
Vitamin D deficiency is more prevalent among older adults for several factors:
* The skin, and kidney loses capacity to make and activate vitamin D
* Spend much of the day indoor
* Drink lesser milk (main dietary source of vitamin D)

22
Q

Vitamin D

Vitamin D toxicity

A
  • From excess supplementation (not from sun exposure)
    Symptoms:
  • over-absorption of calcium (hypercalcaemia), increased calcium excretion
23
Q

Vitamin D

Food sources of Vitamin D

A

Limited range of foods:
* Oily fish (salmon, herring)
* Egg yolks
* Liver
* Margarine in Australia is fortified
>80% of vitamin D in Australia/NZ comes from sun exposure

24
Q

Vitamin E

Forms of Vitamin E

A

8 naturally occuring forms - includes tocopherols and tocotrienols
* most important form is a-tocopherol (alpha)

25
Q

Vitamin E

Main action of Vitamin E

A

Main action of vitamin E is as an antioxidant
* one of our body’s primary defenders against the adverse effects of free radicals
* vitamin E is able to donate an electron to oxidising agents (free radicals)

26
Q

Vitamin E

Free Radicals

A

An uncharged molecule having an unpaired valency electron

27
Q

Vitamin E

Foood Sources of Vitamin E

A
  • Plant oils
  • Wheat germ
  • Sweet potato
  • Peanuts
  • Margarine
  • Nuts and seeds
  • Fatty meats
  • Egg yolks
  • Leafy green vegetables
28
Q

Vitamin E

Vitamin E deficiency

A

Primary deficiency due to inadequate intake is rare
* causes erythrocyte haemolysis (from membrane damage)
* Premature infants at risk
haemolytic anaemia can be treated with vitamin E

29
Q

Vitamin K

How can Vitamin K be obtained other than from food

A

Body: bacteria in the GI tract can synthesis vitamin k that the body can absorb

30
Q

Vitamin K

What are the two natural forms of vitamin K?

A
  1. Phylloquinone (K1 from plants) - directly involved in photosynthesis
  2. Menaquinone (K2; fish oil, meats, and synthesised by gut bacteria)
  • has calcium-binding potential: incolces in bone regeneration (binds calcium; involved in bone formation) - produces specific bone proteins
31
Q

Vitamin K

Vitamin K and Blood clotting

A

Important role in coagulation process (primary in blood clotting) where its presence can make the difference between life and death

32
Q

Vitamin K

Blood Clotting Role

A
  • When blood is exposed to air or foreign substances, platelets (small, cell like structures in the blood) will release a phospholipid known as thromboplastin.
  • Thromboplastin will catalyse the conversion of inactivated proteins such as prothrombin to an activated form (thrombin)
  • Thrombin then catalyses the conversion of the precursor proteins (e.g., fibrinogen to fibrin) to form blood clot (stops bleeding)

Vitamin K essential for formation of prothrombin

33
Q

Vitamin K

Drugs and Vitamin K

A

Anticoagulants:
* lessens blood clotting process
* need to minitor vitamin K intake as can counteract anticoagulant action

Antibiotics:
* destroy intestinal bacteria
* inhibits vitamin K synthesis and absorption
* potential for excessive bleeding

34
Q

Vitamin K

Deficiency of Vitamin K

A

Deficiency causes uncontrolled bleeding
* Characterised by bleeding disorders (from low prothrombin activity)
* Newborns at risk of haemorrhagic disease due to low vitamin K levels (poorly transported across placenta) and sterile gut (no bacteria to produce Vitamin K)
* Also seen with long-term antibiotic use

35
Q

Vitamin K

Food Sources of Vitamin k

A

Liver
Green leafy vegetables – kale, spinach
Avocado, kiwi fruit
Some vegetable oils – soybean oil

*Resistant to cooking losses
Limited vitamin K stored in the body
Toxicity unlikely (readily excreted)

Nutritional Physiology (5 decks)

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