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Year 2 > Vitamin D, Calcium homeostasis and biomineralisation > Flashcards

Vitamin D, Calcium homeostasis and biomineralisation Flashcards

1
Q

Where can vitamin D be made?

A

In the skin with the help of sunlight

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2
Q

What does public health England recommend to adults and children in regards to vitamin D?

A

Advises that adults and children over the age of one should consider taking a daily supplement painting 10 micrograms of Vit D

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3
Q

Name the most potentially toxic vitamin

A

Vitamin D

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4
Q

What can vitamin D cause in high doses?

A

Nausea
Muscle weakness

In very high doses can cause increased calcium absorption and bone resorption

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5
Q

What effect can increased calcium absorption and bone reparation have on the body

A

Increased calcium levels in body fluids can leaf to calcification of arteries and organs eventually leading to liver failure

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6
Q

Give some dietary sources of vitamin D

A
  1. Egg yolk
  2. Fish oil
  3. Some plants
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7
Q

Name the vitamin D precursor

A

Ergosterol or vitamin D2

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8
Q

Is dietary intake of vitamin D usually enough?

A

No exposure to sunlight of consumption of supplements with vitamin D are necessary to prevent deficiencies

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9
Q

What is the first stage of vitamin D activation?

A

Ring cleavage

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10
Q

Name the inactive component of vitamin D found in plants

A

Ergosterol

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11
Q

What happens to Ergosterol when it is hit with UV?

A

It becomes ergocalciferol (vitamin D2)

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12
Q

Name the inactive form of vitamin D formed in our liver

A

7-Dehydrocholesterol

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13
Q

What happens to 7-Dehydrocholesterol when it is hit with UV

A

Cholecalciferol

Vitamin D3

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14
Q

Name the stages involved in vitamin D botsynthesis/activations

A
  1. Ring cleavage

2. Double hydroxylation

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15
Q

How is Cholecalciferol

(Vitamin D3) activated

A

It undergoes double hydroxylation

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16
Q

Go through the steps of the double hydroxylation of Cholecalciferol
(Vitamin D3)

A
  1. Cholecalciferol
    (Vitamin D3) is inactive in the liver
  2. First hydroxylation occurs by enzymes in the liver at position 25
  3. Second hydroxylation occurs in the kidneys at position 1
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17
Q

Where does the double hydroxylation of vitamin D occur?

A

First hydroxylation occurs in the liver

Second hydroxylation occurs in the kidneys

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18
Q

Name the 2 precursors of vitamin D

A
  1. Ergosterol (provitamin D2)

2. 7- Dehydrocholesterol (provitamin D3)

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19
Q

Name the 3 intermediates of vitamin D

A
  1. Ergocalciferol (vitamin D2)
  2. Cholecalciferol (Vitamin D3)
  3. 25-Hydroxycholoecalciferol
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20
Q

Name the activated form of vitamin D3

A

Calcitriol or 1,25- Dihydroxyvitamin D3

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21
Q

Is vitamin D hydrophobic or hydrophilic?

A

Hydrophobic

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22
Q

How is vitamin D transported?

A

It is transported in blood bound vitamin D binding protein (DBP)

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23
Q

What is the half life of 25- hydroxycholecalciferol

A

several weeks

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24
Q

What is the half life of 1,25 dihydroxycholecalciferol

A

A few hours

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25
Q

What can imbalances in calcium serum levels lead to?

A

Can lead to hypercalcaemia and hypocalcaemia

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26
Q

What is the normal range of calcium serum levels a person should be within?

A

2.2-2.7mmol/L

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27
Q

Which hormone is released when calcium levels are low?

A

The parathyroid hormone (PTH)

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28
Q

What does the parathyroid hormone (PTH) do?

A
  1. Enhances bone resorption and increases efflux of Ca2+ from bone
  2. Also decreases the loss of calcium from Turin
29
Q

What response does the body have when it detects low calcium levels in the blood?

A
  1. The parathyroid hormone is released (PTH)
  2. This hormone enhances bone resorption and increases efflux of Ca2+ from bone
  3. Also decreases the loss of calcium from urine
30
Q

Which form of vitamin D is involved in controlling calcium serum levels?

A

Vitamin D3

31
Q

How does vitamin D3 respond when low calcium levels are detected in the blood

A

It enhances absorption of calcium from the intestine

32
Q

Where is vitamin D3 found?

A

In the kidneys

33
Q

Name the glands involved in controlling serum calcium levels

A
  1. Thyroid glands

2. Parathyroid glands

34
Q

What is the parathyroid hormone (PTH) secreted by?

A

Parathyroid glands

35
Q

Does the parathyroid hormone (PTH) increase or decrease serum calcium?

A

Increases it

36
Q

What does parathyroid hormone (PTH) activate indirectly?

A

Osteoclastogenesis

37
Q

What effect does the parathyroid hormone (PTH) have on RANKL and OPG

A

Increases RANKL

Decreases OPG

38
Q

What is calcitonin produced by?

A

Produced by the parafollicular cells in the thyroid

39
Q

What effect does calcitonin have on parathyroid hormone (PTH)

A

It has an antagonistic effect

40
Q

Does calcitonin increase or decrease serum calcium?

A

Decreases

41
Q

What does calcitonin do?

A

It decreases serum Ca2+ by inhibiting osteoclasts

42
Q

The parathyroid hormone (PTH) hormone stimulates the production of C__________

A

Calcitriol

43
Q

What is calcitriol

A

1,25 Dihydroxy vitamin D3

44
Q

What is the production of calcitriol stimulated by?

A

The parathyroid hormone (PTH)

45
Q

What is calcitriol do?

A

It increases calcium absorption in the intestines

46
Q

How does calcitriol increase calcium absorption in the intestine?

A

Vitamin D responsive elements (VDRE) directly regulate gene expression eg osteocalcin

47
Q

Name the enzyme that catalyses the hydroxylation of C25 in the liver

A

25 hydroxylase enzyme

48
Q

Does the 25 hydroxylase enzyme need to be activated?

A

No it is always active and ready to hydroxylate any cholecalciferol and ergocalciferol

49
Q

What can the 25-hydroxylase enzyme be inhibited by?

A

25- hydroxyvitamin D3

50
Q

Talk through when the Parathyroid
Hormone
(PTH) is released and what effect it has on the kidneys

A
  1. Low serum calcium levels are detected
  2. The Parathyroid
    Hormone is released by the parathyroid gland
  3. Hormone travels to kidneys and activated the 1-hydroxylase enzyme
  4. This enzyme then aids het reaction of 25-hydroxyvitamin D3 into 1,25-hydroxyvitamin D3
51
Q

What are al steroid hormone the in body derived from?

A

Cholesterol

52
Q

Where are steroid hormones secreted from?

A

Steroid glands

53
Q

Are steroid hydrophobic or hydrophilic?

A

Hydrophobic (lipophilic)

54
Q

What do steroid do?

A

They directly regulate the expression of certain responsive geneses in conjunction with additional factor

55
Q

Name some common steroids found in the body

A
  1. Cortisol
  2. Testosterone
  3. Vitamin D3
  4. Retinoic acid
56
Q

How are steroid hormones activated and what affect does their activation have?

A

Steroid receptors bind to cognate steroid hormones and become activated
This then activates transcription of target genes

57
Q

What is the human osteroclacin gene responsible for?

A

Biomineralisation and bone matrix synthesis

58
Q

What is human Osteocalcin produced by?

A

Osteoblasts and odontoblasts

59
Q

What does human Osteocalcin do?

A
  1. Binds hydroxyapatite and calcium
  2. Modulated mineralised matrix mechanical properties
  3. It is a marker of matrix mineralising cells
60
Q

What can a deficiency in human Osteocalcin lead to?

A

Osteopetrosis

61
Q

What percentage of the bone matrix is composed of human Osteocalcin?

A

2%

62
Q

How much vitamin D do adults require daily?

A

5-10 micrograms (200-400 iu)

63
Q

State the normal serum levels of vitamin D in an adult

A

25-80ng/ml

64
Q

What can deficiency of vitamin D3 lead to in children?

A

Skeletal mineral deficiencies such as rickets and osteomalacia

65
Q

What can deficiency of vitamin D3 lead to in children?

A

Skeletal mineral deficiencies such as kidney insufficiency and liver cirrhosis

66
Q

What affect can vitamin D3 deficiency has orally?

A
  1. Can increase a patients risk of developing dental caries and periodontal disease
  2. Can lead to enamel and dentine hypoplasia or incomplete/delated development
  3. Can have effects on the alveolar bone
67
Q

What is the significance of vitamin D3 in the mouth?

A

It is necessary for the mineralisation of oral hard tissues including bone an d teeth

68
Q

What does the 25 hydroxylase enzyme do?

A

Ut catalyses the hydroxylation of C25 in the liver (Vitamin D activation)

Year 2 (20 decks)

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