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HUNT241 > Calcium and Vitamin D > Flashcards

Calcium and Vitamin D Flashcards

1
Q

in 1920’s what was the cure that was found for rickets

A

UV light and cod liver oil

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2
Q

what is the main source of vitamin D

A

the sun

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3
Q

other sources of vitamin D

A

cod liver oil
sardines
smoked salmon
eel
fortified soy milk

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4
Q

Is NZ dairy fortified with vitamin D

A

very rarely

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5
Q

how does sunlight provide our bodies with vitamin D

A

UVB light comes through the skin goes through a non enzymatic reaction, causes 7-dehydrocholesterol to form vitamin D3

(action of the sun on the skin does this)

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6
Q

what is shortest wave length of sunlight

A

UVC

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7
Q

what sunlight wavelength has the largest affect on the top layer of the skin and what does it cause

A

UVB - causes burning / redness / skin cancer

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8
Q

why is UBV both problematic and useful

A

has the most use to us but also causes burning / skin cancer

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9
Q

what is the longest wavelength of sunlight

A

UVA = reaches deep into the layers of skin causing aging and wrinkling

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10
Q

what are the behavioural factors that affect vitamin D status

A

clothing (blocks UVB)
sunscreen
time of the day
time spent outdoors
supplements
diet (smaller effect as few foods contain vitamin D)

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11
Q

what are host related factors that affect vitamin D status

A

skin colour (melanin)
-gives the skin, eyes and hair dark colour is the natural protection against the harmful effects of UV light

age- as you get older, your skin is going to have less of the 7-dehydrocholesterol in it, that means lower ability to form vitamin D

sex-in high income countries, men tend to have higher levels than women

BMI- people who are overweight or obese have less circulation vitamin D as it is a fat soluble vitamin (it gets sequested into adipose tissue)

genetic differences in vitamin D binding protein and receptors

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12
Q

what are the environmental factors that affect vitamin D status

A

season
latitude
altitude
clouds
atmospheric pollution

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13
Q

what are the two major forms of vitamin D

A

D2 and D3

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14
Q

where do you get vitamin D3

A

from animals

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15
Q

what type of vitamin D does the skin make when exposed to UV light

A

D3

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16
Q

what is the longer name for vitamin D3

A

cholecalciferol

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17
Q

how is vitamin D3 formed

A

beta ring on 7-dehydrocholesterol is broken by UVB light, this forms pre vitamin D3, then heat converts that to vitamin D3

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18
Q

what does vitamin D2 start out as and how is it converted to D2

A

starts out as ergosterol, B ring is broken down by UVB light, pre vitamin D2 is produced, then heat turns it to vitamin D2

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19
Q

what is the longer name for vitamin D2

A

ergocalciferol

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20
Q

what is the difference between vitamin D3 and D2 in terms of binding affinity and what does this mean

A

vitamin D2 has lower affinity for the vitamin D binding protein, so therefore cleared faster from the circulation

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21
Q

which is more effective, D2 or D3

A

D3

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22
Q

vitamin D is a fat soluble vitamin, so therefore what is needed for it to be absorbed

A

requires fat so it can be absorbed

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23
Q

what are mixed micelles and why is this important

A

vitamin D is soluble in the hydrophobic core of micelle, phospholipids and bile acids surround it

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24
Q

what do bile acids on the outside of a micelle do

A

make the micelle soluble in the hydrophilic gut lumen

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25
Q

once absorbed in the upper small intestine, where is vitamin D transported to

A

transported from the small intestine to the liver by vitamin D binding globulin

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26
Q

is the vitamin D from our food or skin biologically active, what does it require

A

no, it requires metabolic activation in the body

27
Q

how is vitamin D metabolic activated (what happens in the liver then where is this transported to and what happens here )

A

in the liver D3 or D2 will be converted to 25-hydroxyvitamin D (calcidiol)

calcidiol is transported from the liver to the kidney

in the kidney, calcidiol will be converted to 1,25 dihydroxyvitamin D

27
Q

calcitriol is used as a biomarker of what status

A

vitamin D levels

27
Q

what is the active form of vitamin D

A

calcitriol

28
Q

vitamin D floating around your body will be in what form, and if something needs to be done what form will it be in

A

calcidiol = floating round

calcitriol = activated when needed

29
Q

what is the % of vitamin D deficiency in NZ

A

5%

30
Q

where is vitamin D deficiency lowest in NZ

A

Northern regions

31
Q

what is rickets

A

softening of the bones which can lead to fractures and deformity

32
Q

what is heliotherapy

A

sun therapy

33
Q

what is osteomalacia (younger + older adults)

A

softening of the bones

younger adults = bowing of bones

older adults = fractures

34
Q

what is the pain associated with osteomalacia

A

dull aching bone pain, not relieved by rest

35
Q

what is osteoid

A

the bone protein matrix (primarily collagen)

36
Q

in rickets or osteomalacia what happens to osteoid and why

A

insufficient mineral > the osteoid does not mineralise properly > unmineralized osteoid accumulates

37
Q

what is the non bone effect of vitamin D

A

1,25(OH)2D (calcitriol) is the ligand for the vitamin D receptor found in nearly every tissue, controlling hundreds of genes

38
Q

what could lead to vitamin D toxicity

A

supplement / fortification errors

39
Q

what are the non specific symptoms of vitamin D toxicity

A

anorexia, nausea, vomiting, weakness, changes in mental state

40
Q

what are the symptoms of vitamin D toxicity related to high blood calcium levels

A

high blood calcium levels > vascular and tissue calcification > damage to the heart and kidneys : may be fatal

41
Q

when does bioavailability of calcium decrease

A

decrease with age

42
Q

what is the bioavailability of calcium in dairy products

A

~30%

43
Q

what foods decrease the bioavailability of calcium

A

foods rich in oxalic acid or phytate

44
Q

what are the two mechanisms of calcium absorption

A

absorption by active active transport = requires vitamin D

passive diffusion = increasingly important as Ca intakes increase

45
Q

for the body to function the serum calcium must be within the narrow range of …

A

2.12-2.62nmol/L

46
Q

what maintains the serum calcium levels

A

levels maintained through an endocrine system with strict controlling factors and feedback mechanisms

(calcitriol and parathyroid hormone play key roles in this)

47
Q

drop in calcium levels in the blood stimulates what

A

parathyroid gland to release PTH

48
Q

in response to PTH release, what will happen

A

calcium released from the bones will increase

and

calcium uptake in the kidneys will decrease

and

stimulate calcitrol to be released from the kidneys

49
Q

what will release of calcitriol cause

A

the calcium in the intestines will have increased absorption

50
Q

how does negative feedback associated with calcium and PTH work

A

as calcium levels increase in the blood, your PTH levels begin to drop

51
Q

if calcium levels get too high what will be increased from the thyroid gland

A

calcitonin is released which will block the bone calcium absorption

52
Q

almost 98% of the total body calcium is found where and in what form

A

as calcium hydroxyapatite in bones and teeth

53
Q

the other 2% of total body calcium is critical for what

A

vascular contraction and
vasodilation

muscle function

nerve transmission

intracellular signalling

hormone secretion

54
Q

what is reduced bone strength

A

osteoporosis

55
Q

calcium deficiency can be hypocalcaemia, what can this also be caused by

A

usually due to vitamin D or magnesium deficiency or hypoparathyroidism (underperforming parathyroid glands)

56
Q

what are the wide range of symptoms associated with hypocalcaemia

A

perioral numbness, tingling hands and feet, muscle spasms

renal and brain calcification, depression, heart failure, seizures, coma

57
Q

how common is calcium toxicity

A

rare in healthy people

58
Q

calcium toxicity is usually a result of

A

cancer

primary hyperparathyroidism

59
Q

what does calcium toxicity result in

A

poor muscle tone

renal insufficiency

constipation

nausea

weight loss

fatigue

higher risk CVD mortality

60
Q

actions of 1,25(OH)2D - calcitriol

A

promotes intestinal absorption of calcium and phosphate

increases calcium reabsorption from kidney

direct action of cartilage and bone to promote normal skeletal development and turnover

inhibits PTH

61
Q

thinning of bone mass is due to imbalance in what

A

imbalance in bone resorption and formation

HUNT241 (19 decks)

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