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Advanced Nutrition II - Exam 2 > Vitamin D > Flashcards

Vitamin D Flashcards

1
Q

What % of vitamin D in blood is transported by chilomicrons

A

40

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2
Q

What is cholecalciferol

A

A form of vitamin D synthesized in the skin

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3
Q

Explain the 3 step process of cholecalciferol starting from the skin

A
  • Cholecalciferol diffuses from skin into blood & is picked up by vitamin D-binding protein (DBP) for transport
  • Hydroxylated to 25-OH D3 in liver by CYP-450 hydroxylases
  • 25-OH D3 secreted into blood, transported by DBP
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4
Q

What is the main form of vitamin D

A

25-OH D3 is the main form of vitamin D in the body and reflects vitamin D status

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5
Q

What are normal ranges for serum vit D

A

25-OH D3 are between 30-40 ng/mL or 75-100 nmol/L

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6
Q

What happens to vitamin D in response to PTH

A

25-OH D3 is picked up by kidneys

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7
Q

What are the kidneys effect of 25-OH D3

A

Kidneys hydroxylate 25-OH D3 by 1- hydroxylase (CYP27B1) to form calcitriol

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8
Q

What is the active form of vitamin D

A

Calcitriol

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9
Q

What is the transporter for calcitriol in the blood

A

DBP

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10
Q

What are the 2 hormones that regulate calcitriol

A

PTH and fibroblast-like growth factor (FGF) 23

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11
Q

When is PTH secreted

A

–Secreted when calcium and phosphorus levels in blood are low

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12
Q

What is the effect of PTH

A

–Stimulates synthesis of 1-hydroxylase

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13
Q

Where is FGF 23 synthesized

A

–Secreted by osteocytes and osteoblasts

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14
Q

What is the effect of FGF 23

A

–Inhibits the synthesis of 1-hydroxylase

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15
Q

How else can 1-hydroxyl are be inhibited

A

High calcium and phosphorus

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16
Q

What is the main nongenomic function of calcitriol

A

Serum Calcium homeostasis

17
Q

What is the mechanism of action of nongenomic calcitriol function

A

acts by generation of second messengers (MAP kinase, PKC, cAMP, Tyrosine kinase, inositol, etc)

18
Q

What are the 3 functions of second messengers

A

–Increase calcium uptake
–Increase intracellular calcium concentration –Increase transcellular calcium flux in enterocytes, osteoblasts, adipocytes, skeletal muscle

19
Q

What is the main genomic function of calcitriol

A

Modulation of gene transcription by going to the nucleus of cells

20
Q

In what 2 ways does calcitriol modulate gene transcription

A
  • Calcitriol diffuses into the nucleus and binds to vitamin D receptors (VDRs)
  • Modulation of transcription of genes encoding for proteins related to calcium homeostasis (osteocalcin, osteopontin, 24-hydroxylase, calbindin)
21
Q

How can calcitriol interact with mRNA

A

To change translation

22
Q

Normal serum calcium levels

A

Normal serum calcium 8.5 to 10.5 mg/dL (2.12–2.62 mmol/L)

23
Q

What collectively happens when calcium levels are low

A

–PTH stimulates 1-hydroxylase activity in the kidneys
–Calcitriol increases calcium absorption in the intestine by stimulating expression of calcium channel transporter TRPV6, calbindin D9k and enhances extrusion of Ca across the basolateral membrane of the intestine by stimulating expression of Ca2+ ATPases
–Calcitriol exerts a similar effect in the kidneys by increasing gene expression of TRPV5 and calbindin D28k

24
Q

In what 2 ways does calcitonin decrease serum calcium

A

–Blocks calcium and phosphorus mobilization from bones by inhibiting osteoclast activity
–Inhibits tubular resorption of calcium increasing urinary calcium losses

25
Q

What is calcitriol effect on phosphorus

A

Decreases serum levels

26
Q

What does calcitriols effect on phosphorus help maintain

A

May help maintain normal cell growth, differentiation and proliferation

27
Q

How are vit D metabolites excreted

A

Metabolites excreted in feces (>70%) & urine

28
Q

RDA for vitamin D

A

600 IU (15 µg) of vitamin D for ages 1 - 70 800 IU (20 µg) of vitamin D for adults older than 70 years of age.

29
Q

What amount of time must you be in the sun to get adequate vitamin D

A

•5 – 15 minutes sun exposure daily

30
Q

What factors make it harder to synthesize vitamin D

A

•Older persons, those with darker skin, those living further north will need more

31
Q

Symptoms of vit D deficiency

A

–Vomiting
–Diarrhea
–Use of medications (BP medications like thiazides and loop diuretics)

32
Q

6 Hypokalemia symptoms

A

(low plasma potassium) –Cardiac arrhythmias –Muscular weakness – Nervous irritability – Hypercalciuria -glucose intolerance -mental disorientation

33
Q

3 Symptoms of moderate vitamin D deficiency

A

–Elevated blood pressure
–Abnormal bone turnover
–Elevated calciuria

34
Q

What is the effect of hyperkalemia on the body

A

associated with impaired kidney function

35
Q

2 Symptom of hyperkalemia

A

–Cardiac arrhythmias –Cardiac arrest

36
Q

Why can’t humans utilize phytic acid

A

Do not have the enzyme

37
Q

What are the 2 main transporters for vitamin D

A

Chilomicrons

Vitamin D binding protein (DBP)

Advanced Nutrition II - Exam 2 (12 decks)

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