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Nutrition 446 > Vitamin D > Flashcards

Vitamin D Flashcards

0
Q

Symptoms of rickets in infants and children?

A

Bones become soft and pliable due to inadequate mineralization; epiphysial cartilage continues to grow and enlarge without replacement of bone matrix and minerals

Bowed legs, enlarged knee joints
Crainotabes (soft spots in the skull)

Delayed closing of fontanelles
Delayed formation of teeth
Architect rosary
Poorly formed pelvis

Deformation of long bones are permanent

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1
Q

Vitamin d deficiency in infants and children?

A

Rickets

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2
Q

Vitamin D deficiency in adults

A

Osteomalacia

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3
Q

Symptoms of osteomalacia

A

Minerals are removed from bone - bones become soft and brittle, distorted
Constant rheumatic type pain; waddling gait

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4
Q

Causes of vitamin d deficiency

A

Low dietary intake of calcium and or vitamin d and a lack of exposure to sunlight

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5
Q

Who is susceptible to vitamin d deficiency?

A

Mainly occurs in the elderly in US and Europe
Infants
People with parathyroid, liver and or kidney diseases

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6
Q

Causes of vitamin D toxicity

A

Dietary ingestion of large amounts of vitamin d (most likely of all vitamins to cause reaction)

Exposure to sunlight poses no risk of toxicity

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7
Q

Symptoms of mild vitamin D toxicity

A 
Anorexia
Excessive thirst
Nausea/vomiting
Constipation 
Failure to grow
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8
Q

Symptoms of severe vitamin D toxicity

A 
Calcification of soft tissues such as heart, kidneys, lung, pancreas
Mental retardation
Uremia
Death from heart failure
Fetal damage from high maternal intake
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9
Q

Sources of dietary vitamin d

A

Animal foods- liver, beef, veal, eggs, saltwater fish

Dairy and orange juice are fortified

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10
Q

Non dietary source of vitamin D

A

7 - dehydrocholesterol is synthesized in skin

  • allows for absorption of specific wave lengths of light
  • exposure to sunlight converts it to previtamin D3
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11
Q

Vitamin D is found in diet as?

A

Cholecalciferol (D3)

Ergocalciferol (D2) in plants

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12
Q

Absorption of vitamin d

A

Dietary vitamin d3 (cholecalciferol) is absorbed from micelles and transported to the liver

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13
Q

Transport of vitamin D

A

Vitamin d binding protein - is synthesized in the liver
Binds all forms of vit d and transports 60% to liver and extra hepatic tissues
Bound to calcidiol (25-OH-VD3)

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14
Q

What is the precursor to active Vit D3

A

25-OH-VD3 (calcidiol)

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15
Q

Vitamin D hydroxylation

A

Cholecalciferol in the liver is meTabolized by calciferol hydroxylase to generate inactive Vit d calcidiol (25-OH-VD3) - precursor to active vD3 calcitriol

16
Q

Step 1 of Vit D hydroxylation

A

Calciferol hydroxylase (a mitochondrial enzyme, cytochrome p50 hydroxylase, NAPDH dependent)

Hydroxylates cholecalciferol at carbon 25

Efficient during low Vit D intake

17
Q

Step 2 of vitamin D hydroxylation

A

25-OH-VD3 (calcidiol) that is bound to DBP in the blood is taken up by the kidneys

25-hydroxy vitamin D 1-a-hydroxylase (NADPH dependent mitochondrial enzyme)

hydroxylyzes it to 1,25-(OH)2VD3 (calcitriol) - active form

18
Q

Regulation of 25-hydroxy vitamin D 1-a-hydroxylase

A

Hydroxylates calcidol to calcitriol

High levels of calcitriol and phosphorus inhibit it, low levels enhance it

19
Q

Alternative inhibition of calcitriol

A

24-hydroxylase convertes (25-OH-VD3) (calciferol) to 24,25-(OH)2VD3

When calcitriol is high it is enhanced

20
Q

Active form of Vit D3

A

1,25-(OH)2VD3 (calcitriol) - active form

21
Q

Genomic actions of Vit D3

A

Analogous to Vit A

Stimulates differentiation of hematopoietic cells and intestinal cells
Osteoblasts to produce osteoclast differentiation factors

Reduces cell proliferation (fibroblasts, keratinocytes and lymphocytes
Cancer cell
Treatment of skin disorders
Bone disease, hyperparathyroidism

22
Q

Non genomic actions of Vit D

A

Signal transduction pathways linked to cell membrane Vit D receptors

Binding of calcitriol to VDR causes:
1. Phosphorylation/dephosphorylation of enzymes

  1. Activation of 2nd messengers - protein kinase C, cAMP, phospholipase c, arachidonic acid, diacylglycerol, insositol phosphate

Results in opening of Gated Ca channels and increased Ca uptake by intestine osteoblasts and muscle cells

23
Q

2nd messengers activated by active Vit D3

A

protein kinase C, cAMP, phospholipase c, arachidonic acid, diacylglycerol, insositol phosphate

Results in opening of Gated Ca channels and increased Ca uptake by intestine osteoblasts and muscle cells

24
Q

Vitamin D role in calcium homeostasis

A

Calcitriol acts with PTH to maintain blood calcium levels

-Synthesis is stimulated in response in changes in blood calcium

25
Q

What happens in response to hypocalcemia

A

Secretion of PTH is stimulated
PTH stimulated the 1-a-hydroxylase in the kidney
The synthesis of calcitriol is secreted
Calcitriol acts on target tissues to increase serum calcium levels (small intestine, bone and kidneys)

26
Q

Main targets of calcitriol

A

small intestine, bone and kidneys

27
Q

Effects of calcitriol on the kidney

A

increases expression of calbindin28 to increase renal calcium reabsorption

28
Q

Effects of calcitriol on the bone

A

Stimulates osteoclast activity to direct the mobilization of Ca and P from bone and help maintain normal Ca levels

29
Q

Effects of calcitriol on the intestine

A

Increase the absorption of Ca & P

It functions through cell surface and nuclear receptors

30
Q

What is calbindin28

A

increases the renal calcium reabsorption

31
Q

Genomic effects of calcitriol on the intestine

A

Binds to the VDR which increases the transcription of callbindin9
Increases the absorption and transport of Ca

32
Q

Non-genomic effects of calcitriol on the intestine

A

Indices changes in brush border composition and topology to increase absorption

Nutrition 446 (12 decks)

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