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IBMS SR > Vitamin D, Calcium Homeostasis and Biomineralisation > Flashcards

Vitamin D, Calcium Homeostasis and Biomineralisation Flashcards

1
Q

how is vitamin D made

A

in the skin

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2
Q

what supplement amount shall we take of vitamin D

A

10 micrograms of vitamin D

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3
Q

what can high doses of vitamin D cause
v high doses

A

Nausea and muscle weakness

very high doses cause calcium absorption and bone resorption

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4
Q

what is the issue with calcium absorption

A

can lead to calcification of the arteries organs and kidney failure

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5
Q

what are some sources of vitamin d

A

EGG YOLK FISH OIL

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6
Q

WHAT IS THE plant vitamin D PRECURsor CALLED

A

ergosterol (provitamin D2)

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7
Q

what is the inactive precursor for vitamin d from our liver

A

7 dehydrocholesterol (vitamin d3)

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8
Q

what is step 1 of the biosynethesis of vitamin D

A

ergosterol and 7-dehydrocholestrol move to skin
UV light cleaves ring
ergosterol is converted to ergocalciferol in plants
7-dehydrocholestrol is converted to cholecalciferol in humans

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9
Q

what is produced at the end of stage 1 biosynthesis of vitamin D in plants

A

ergocalciferol

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10
Q

what is produced at the end of stage 1 biosynthesis of vitamin D in the liver

A

cholecalciferol (inactive)

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11
Q

what is step 2 of the biosynethesis of vitamin D

A

double hydroxylation

where cholecalciferol turns into 1,25 dihydroxyvitamin D3 (active) via enzymes in the kidney and liver

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12
Q

why is the molecule called 1,25 dihydroxyvitamin D3

what is another name for it

A

due to the position of hydroxylation
1st hydroxylation is position 25 in the liver
2nd hydroxylation is position 1 in the kidney

calcitriol

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13
Q

where does the first hydroxylation the active form of vitamin D3 occur

A

position 25 in the liver

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14
Q

where does the second hydroxylation the active form of vitamin D3 occur

A

position one in the kidney

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15
Q

how is cholesterol transported

A

in blood bound vitamin D binding protein (DBP)

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16
Q

what is the half life of 1,25 dihydroxycalciferol

what is the half life of 25-hydroxycholecalciferol

A

only a few hours

several weeks

17
Q

is vitamin d hyprophobic or hydrophilic

A

hydrophobic

18
Q

what should the calcium serum levels be in homeostasis

A

2.2-2.7 mmol/litre

19
Q

what can calicum imbalance lead to

A

hyper and hypocalcaemia- can have life threatening consequences eg in muscular contractions

20
Q

how is low calcium levels detected

A
  1. in the blood
  2. parathyroid hormone released from parathyroid glands
  3. effects bone- enhanced bone resorption and increased efflux of calcium ions
  4. effects kidney- PTH decreases loss of calcium in from the urine (to maintain serum calcium levels). Also releases active vitamin d3 which increases absorption of Ca from dietary sources in the intestines
21
Q

describe the PTH hormone

A 
short half life 
rapid response 
triggers the PTH receptor 1 in bone 
upregulate RANK ligand 
down-regulate osteoprotegerin 
activates osteoclastogenesis
22
Q

how is calcitonin produced

A

by parafollicular cells in the thyroid

inhibits osteoclasts and therefore bone is not resorbed so reduces calcium ions serum

23
Q

how is calcitriol produced

A

stimulated by the PTH in kidney

increases the calcium absorption in intestine

24
Q

what can help regulate gene expression

A

vitamin d responsive elements

25
Q

give examples of vitamin d responsive elements

A

osteocalcin

26
Q

how does the hydroxylation of vitamin d3 occur

A

by the 25 hydroxylase enzyme

27
Q

how is the hydroxylation of the 1,25 dihydroxyvitamin D3 regulated

A

the inhibition of the 25 hydroxylase enzyme by 25 hydroxyvitamin D

28
Q

where are steroid hormones derived from

A

cholesterol secreted by steroid glands

29
Q

how does vitamin D signalling occur

A

steroid receptor bind to cognate steroid hormone become activated and activate transcription of target genes

30
Q

which gene is involved in bone matrix

A

human osteocalcin gene

31
Q

what is human osteocalcin produced by

A

osteoblasts and odontoblasts

32
Q

what does human osteocalcin do

A

binds hydroxyapatite and calcium crystals

33
Q

what can deficinecy of vitamin d3 LEAD TO

A

Skeletal mineralisation deficiency

34
Q

what can deficinecy of vitamin d3 LEAD TO in children

A

rickets and osteomalacia

35
Q

how might vitamin d deficiency affect the oral cavity

A

increase risk of developing dental caries and perio disease

IBMS SR (38 decks)

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