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NUTR*3210 > UNIT 9: MICRONUTRIENTS I: Vitamin D, Calcium, Phosphorus, Fluoride > Flashcards

UNIT 9: MICRONUTRIENTS I: Vitamin D, Calcium, Phosphorus, Fluoride Flashcards

1
Q

Vitamin D is a _____ vitamin

A

fat soluble

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2
Q

What is the precursor to vitamin D?

–> vitamin D via?

A

5-dehydrocholesterol

via exposure to UV light –> vitD

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3
Q

What are the sources of vitD?

A
  • plant + animal food sources

- human conversion from sunlight

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4
Q

Plants make vitamin ____

Animals make vitamin ____

A

Plants: D2 = ergocalciferol
Animals: D3 = cholecalciferol

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5
Q

What are the metabolic fates of vitD3 (cholecalciferol) in the body?

A
  • calcidol (25-OH VitD)

- calcitriol (1,25-diOH VitD)

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6
Q

Explain the steps of vitD synthesis from sunlight in animals.

A

vitamin D is synthesized as vitD3 (cholecalciferol)
1. 7-dehydrocholesterol in keratinocytes of skin
sunlight/UV breaks one ring –> pre-vitD
2. Heat/infrared converts
pre-vitD –> vitD3

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7
Q

How is excess vitamin D3 prevented from entering circulation?

A
  • UV irradiation converts

pre-vitaminD3 –> lumisterol and tachysterol (biologically inactive, reversible, pool)

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8
Q

Vitamin D3 diffuses into the blood if _____

A
  • binding sites available on circulating D binding protein (DBP)
  • if saturated, D3 stays in keratinocytes to prevent toxicity in blood
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9
Q

What are 2 pathways of vitamin D?

A
  1. synthesis following exposure to UV light

2. diet

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10
Q

How is vitD3 synthesized in the body?

A
  • sunlight converts 7-dehydrocholesterol –> vitD3 in keratinocytes
  • vitD3 diffuses to blood if DBP binding sites available
  • delivered to liver or adipose for storage
  • liver: vitD3 –> 25-OH vitD
  • 25-OH vitD binds DBP again to kidney
  • kidney: 25-OH vitD –> 1,25-diOHvitD
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11
Q

What is the active form of vitD? Where is it formed? What does it bind to?

A

1,25di-OH vitD
formed in the kidney
binds to DBP - type II SHR

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12
Q

Where is the active form of vitD found in?

A

formed in kidney

also in intestine, bone

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13
Q

What is the role of 1,25-diOH vitD?

A

active form

- increase calcium in body

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14
Q

What are sources of dietary vitD?

A

supplements, fortified foods, some animal products, minimal from plants

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15
Q

How does dietary vitD enter the body?

A
  • vit D3 incorporated into micelle passively and incorporated into chylomicron
  • chylomicron circulates and degraded (nothing happens to vitD3 in the circulation)–> chylomicron remnant
  • remnant goes to liver where metabolism is same as from skin
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16
Q

Which form of vitD is used as a homeostatic setpoint? (pools of vit D3 in the blood)

A

25-OH vitamin D bound to DBP

  • indicator of low vitamin D
  • inactive form

vitaminD3 bound to DBP is NOT a homeostatic setpoint
calcitriol is NOT setpoint

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17
Q

What is calcidiol?

A

25-OH vitD

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18
Q

What is calcitriol?

A

1,25-OH vit D

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19
Q

Calcidiol/calcitriol.

Which is active form?

A

Calcitriol 1,25-diOH vitD

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20
Q

Calcidiol/calcitriol.

Which is homeostatic setpoint?

A

Calcidiol 25-OHvitD

- low levels = vitD deficiency

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21
Q

What is the main biological roles of vitD?

A
  • regulating blood calcium homeostasis

via calcitriol in bone, intestine, kidney

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22
Q

What are other roles of vitamin D?

A
  • cell proliferation
  • cell differentiation
  • inflammation
  • immune function
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23
Q

There are 2 pathways of calcitriol:

A
  1. calcitriol binds vitD receptor VDR in nucleus to regulate gene expression
  2. calcitriol binds membrane associated rapid response steroid receptor MARRS
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24
Q

Which organs are involved in calcium homeostasis? What are the functions?

A

small intestine (absorption)
kidney (reabsorption)
bone (resorption)

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25
Q

Which 3 hormonal control systems maintain homeostasis?

A
  • parathyroid hormone
  • calcitriol
  • calcitonin
26
Q

Which hormonal responses are for low blood calcium?

A

PTH

calcitriol

27
Q

Which hormonal responses are for high blood calcium?

A

calcitonin

28
Q

What does PTH do?

A

parathyroid hormone

  • 1st response to LOW blood calcium
  • stimulates calcitriol production in kidney
  • stimulates bone resorption (osteoclasts)
  • tubular reabsorption of calcium in kidney
29
Q

What does calcitriol do?

A
  • 2nd response to low blood calcium
  • kidney: active metabolism of vitD
  • increase blood calcium
  • bone resorption (long term)
  • calcium absorption small intestine (short term)
  • tubular reabsorption of calcium in kidney (short term)
30
Q

What does calcitonin do?

A
  • response to HIGH blood calcium
  • calcitonin secreted by: thyroid parafollicular cells
  • decrease blood calcium
  • suppress tubular reabsorption in kidney
  • inhibit bone resorption
  • facilitate remineralization (long term - improve bone density)
31
Q

Vitamin D deficiency causes decreased levels of ___

A

calcitriol (active)

facilitates calcium absorption/reabsorption/resorption

32
Q

Low vit D = decr. calcitriol leading to:

A
  • decreased intestinal calcium absorption
  • decreased tubular calcium reabsorption
  • not decreased bone resorption (even though an action of calcitriol, but decreasing this is dangerous)
33
Q

Rickets?

A

vitamin D or calcium deficiency in infants

= softening of bown

34
Q

Osteomalacia?

A

vitamin D or calcium deficiency in adolescents

= demineralizing bone = frequent fractures

35
Q

Osteoporosis?

A

middle aged to elderly

- bone loss of density/mass

36
Q

What is the difference between osteomalacia and osteoporosis?

A
  • osteoporosis: loss of bone mass and density as a normal part of aging; minerals and organic bone lost
  • osteomalacia: demineralization due to deficiency of nutrients; minerals lost
37
Q

What are the health consequences of vit D toxicity

A

no risk for toxicity

UL 4000IU

38
Q

Calcium micro/macro?

A

macromineral

39
Q

What is the role of calcium?

A
  • mineralization in tissues (bone and teeth)

- cell signalling

40
Q

What are the 3 main stores of calcium?

A
  • intracellular (mitochondria, ER, SR)
  • blood calcium (protein bound)
  • bone calcium (99%)
41
Q

What are the toxic effects of calcium?

A

hypercalcemia

- biliary/kidney stones from excess mineral

42
Q

What is vitamin K?

A

fat soluble vitamin

43
Q

What is the role of vitamin K?

A

(K)oagulation

44
Q

What are the sources of vitamin K?

A

Plants: leafy greens phyloquinone

Bacteria

(little vit K storage in body)

45
Q

What is the active form of vitamin K?

A 
reduced = active
oxidized = inactive
46
Q

Where is vit K synthesized in the body?

A

colonic synthesis of menaquinone vitK

47
Q

Vit K1 is:

A
  • in plants
  • phylloquinone
  • w/ saturated side chain
48
Q

Vit K2 is:

A
  • in bacteria
  • menaquinone
  • w/ unsaturated side chain (double bonds present)
49
Q

What is vit K needed for?

A
  • post-translational modfication of glutamate residues –> gamma-carboxyglutamate (important to bind proteins)
50
Q

How is vit K related to Ca2+?

A
  • Pre-calcium binding proteins with glutamate side chains
  • pre-protein undergoes carboxylation via vitK coenzyme
  • forms y-carboxyglutamate side chain (- -)(ionized/deprotonated)
  • ca++ can bind
51
Q

What are the effects of vit K toxicity?

A

nothing

52
Q

What are the effects of vit K deficiency?

A

impaired blood clotting

  • decreased bone density
  • hemmorrhagic syndrome (infants because impaired calcium binding)
  • increased osteoporosis in elderly
53
Q

What is phosphorus?

A

macromineral

54
Q

Where is phosphorus predominantly found?

A

in bone with calcium

55
Q

What are the roles of phosphorus?

A
  • metabolism (ATP, cAMP, cGMP, DNA, RNA)

- protein phosphorylation

56
Q

Sources of phosphorus?

A
  • animal products (more)

- cereals and soy

57
Q

Most of the phosphorus in grains is ___

A

phytic acid

80%

58
Q

Toxicity of phosphorus?

A

rare, but can imbalance calcium from urinary loss

59
Q

What is fluoride?

A

micromineral

60
Q

What is fluoroapa tite?

A

increases resistance of tooth enamel to acid degradation

61
Q

Where is fluoride found?

A

bones

NUTR*3210 (15 decks)

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