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NPLEX I 2024 > Biochem (Vitamins) > Flashcards

Biochem (Vitamins) Flashcards

1
Q

What are the main functions of vit D

A

Ca homeostasis
bone metabolism
Dec PTH

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2
Q

What is the metabolically active form of vita D

A

Calcitriol

Ercalcitriol

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3
Q

What kind of hormone is vit D

A

Steroid

Made from cholesterol, fat soluble

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4
Q

What inactive molecules preceed active vit D

A 
Vit D2 (ergocalciferol)
Vit D3 (cholecalciferol)
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5
Q

How do D2 and D3 from our diet become active?

A

Carried around by vit D binding proteins

Eat > get packaged in small int with bile salts into micelles > absorbed in enterocytes > incorporated into chylomicrons (lipoproteins) > lymph > blood > liver > hepatocyte ER

25-hydroxylase adds hydroxyl group to both molecules

D2 > ercalcidiol
D3 > calcifediol

Re-enter blood still bound to vit D binding protein

Liver > prox tubules of kidneys > renal cell mitochondria > 1 alpha hydroxylase adds hydroxyl group to both >

Ercalcitriol
Calcitriol

> active vitamin D

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6
Q

vit D3 synthesis from sun exposure

A

Sun exposure > 7 dehydrocholesterol, a precursor for cholecalciferol, absorbs UV B radiation > photolysis > pre vitamin D3 > cellular heat isomerizes pre vitamin D3 > vit D3 (cholecalciferol) > same path through liver and kidneys

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7
Q

Where is 7 dehydrocholesterol found

A

Keratinocytes in stratum spinosum and stratum basale

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8
Q

Low phosphate effects on vit D

A

Low phos > inc 1 a hydroxylase > active vit D transported to various tissues

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9
Q

Where are vit D receptors

A

Cytoplasm

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10
Q

Vit D role in nucleus

A

Stim transcription of genes and synthesis of protein

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11
Q

Vit D role in bones

A

Binds to vit D receptors on osteoblasts > release cytokines > RANKL + MCSF > fuse macrophage precursors together to form osteoclasts > break down bone > release Ca and phos into blood

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12
Q

Vit D role in enterocytes

A

Inc Ca and Phos absorption via stim synthesis of calbindin D 28 K (Ca binding protein)

Causes enterocytes to inc synthesis of sodium phos co-transporters > inc phos absorption

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13
Q

Vit D role in kidneys

A

Principal cells of DCT > stim synthesis of calbindin D28K > allowing more Ca reabsorp form urine

Tubular cells of PCT > causes inc synthesis of Na/Phos contransporters on apical surface > inc phos reabsorp

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14
Q

Where do we get vit D2

A

Plant sources in diet

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15
Q

Where do we get D3

A

Animal dietary or sun

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16
Q

What organs convert D2 and D3 to active vit D

A

Liver and kidney

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17
Q

Activation of vit D is triggered by:

A

PTH, when Ca/Phos levels are low

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18
Q

Effects of activated vit D

A

Stim bone resorption

Stim Ca/Phos reabsorption in small intestines and kidneys

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19
Q

PTH vs Vit D effects on Ca and Phos

A

PTH: inc Ca, dec Phos

Vit D: inc Ca, inc Phos

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20
Q

What are the fat soluble vitamins

A

Vit D
Vit E
Vit K
Vit A

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21
Q

What are the water soluble vitamins

A 
B9 (folate)
B7 (biotin)
B6 (pyridoxine)
B5 (pantothenic acid)
B3 (niacin)
B2 (riboflavin)
B1 (thiamine)
B12 (cobalamin)
C
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22
Q

what is the first hydroxylation step of vit D conversion and where does it take place

A

liver

25-hydroxylase converts
vit D2/D3 > 25-hydroxyvitamin D (main storage form)

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23
Q

what is the second hydroxylation step of vit D conversion and where does it take place

A

kidneys

1-alpha hydroxylase converts
25-hydroxyvitamin D > 1,25-dihydroxyvitamin D (active)

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24
Q

causes of vit D deficiency

A 
lack of dietary intake
infants exclusively breastfed
reduced sunlight exposure
pigmented skin tones 
advanced liver disease 
CKD 
malabsorptive disorders (cystic fibrosis, celiac, chronic pancreatitis)
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25
Q

malabsorptive disorders effect absorption of what vitamins

A

fat soluble

A, D, E, K

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26
Q

vit D def sx

A

low 25 hydroxy vit D
low Ca, low Phos
hyper PTH (low ca over long time)

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27
Q

bone disorders associated with severe vit D deficiency

A

rickets

osteomalacia

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28
Q

high vitamin D sx

A

sx of hypercalcemia

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29
Q

excess vit D causes

A

granulomatous disorders

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30
Q

retinol common name

A

vit A

31
Q

folate common name

A

B9

32
Q

biotin common name

A

B7

33
Q

pyridoxine common name

A

B6

34
Q

pantothenic acid common name

A

B5

35
Q

niacin common name

A

B3

36
Q

riboflavin common name

A

B2

37
Q

thiamine common name

A

B1

38
Q

cobalamin common name

A

B12

39
Q

vit A precursors/sources

A

beta-carotenes and retinol esthers (both from dietary sources)

40
Q

retinol absorption, conversion, and storage

A

retinol absorebd in small intestine > converted into retinol esthers > picked up by chylomicrons > stored in liver stellate cells

41
Q

retinol crosses cell membrane and enters nucleus in what form, to do what

A

retinoic acid > modify gene transcription

42
Q

vit A main functions

A

orderly cellular differentiation and maturation

vision

43
Q

vit A vision effects

A

retinol is part of rhodopsin (light sensitive protein important for photo transduction) >
sharpen vision and image

44
Q

causes of vit A deficiency

A 
lack of dietary vit A (rare)
vit C deficiency
pancreatic insufficiency (cant produce enzymes that break fat)
intestinal malabsorption (IBD, bariatric surgery)
cholestatic liver disease (bile is stuck in bile ducts; cant emulsify fat)
45
Q

vit A def sx

A

impaired night vision/nyctalopia (impaired rhodopsin formation)
blindness in severe cases (metaplasia of cornea, corneal epithelium keratinizes - keratomalacia)
bidot spots in conjunctival epithelium - conjuntival squamous metaplasia - localized keratin debris

inc risk of pnemonia (due to squamous metaplasia)

squamous metaplasia of pancreatic exocrine ducts (esp due to def caused by CF)

growth disturbances
kidney stones

46
Q

acute vit A toxicity sx

A

blurry vision
vertigo
N/V

47
Q

chronic vit A toxicity sx

A 
hepatic toxicity and enlargement
cheilitis (lip inflammation)
arthralgias 
alopecia 
hyperkeratosis (dry, thickened skin)
pseudotumor cerebri (idiopathic intracranial hypertension ICH) > inc CSF pressure, papilledema)
48
Q

vit A derviatives (s/a isotretinoin) contraindications

A

pregnancy

highly teratogenic

49
Q

vit E exists in how many forms

A

8 tocopherols/tocotrionals

50
Q

most biologically active form of vit E

A

alpha-tocopherol

51
Q

vit E functions

A

cell membrane protection via neutralizing free radicals (antioxidant)
prevents oxidation of LDL
neuroprotection (may slow decline in alzheimers)

52
Q

vit E deficiency causes

A 
dietary intake (rare)
fat malabsorption (pancreatic insufficiency, cholestatic liver dz, bariatric surgery)
genetic: abetalipoproteinemia, AVED (ataxia w vit E def)
53
Q

vit E def sx

A 
hemolytic anemia (lack of ROS protection, RBCs pop/hemolyze)
acanthocytes (spur cells)
muscle weakness (skeletal myopathy) 
unsteadiness
loss of coordiantion, ataxia
slurred speech
difficulty swallowing
affects spinocerebellualr tracts
loss of position/vibration sense 
loss of DTR
infertility (males)
low serum phospholipids
similar to B12 sx
54
Q

vit E toxicity sx

A

interferes with vit K metabolsim
inc bleeding with warfarin
inc risk of hemorrhagic stroke
necrotizing enterocolitis in infants

55
Q

vit E high dose indications

A

age related macular degeneration

NAFLD

56
Q

vit K natural forms

A

phylloquinone, menaquinone

57
Q

vit K natural forms

A

phylloquinone, menaquinone

58
Q

main source of vit K

A

leafy green veggies, gut flora

59
Q

vit K activation

A

oxidized inactive vit K converted to reduced active vit K via VKOR (vit K epoxide reductase)

60
Q

vit K is a cofactor for

A

gamma-glutamyl carboxylase (GGC), which catalyzes the post translational modification of the vit K dependent proteins: factors 2, 7, 9, 10, C, S

61
Q

causes of vit K def

A 
inadequate dietary intake 
fat malabsorptive disorders
prolonged use of broad spectrum antibiotics (eradicate gut flora that produce vit K)
warfarin
newborns
62
Q

what drug can mimic vit K def sx

A

warfarin; blocks VKOR which blocks vit K activation

63
Q

reasons why newborns more likely to develop vit K deficiency

A

breastmilk low in vit K
dont have fully developed liver
no gut bacteria/sterile guts
doesnt cross placenta

64
Q

vit K def sx

A 
bleeding diathesis 
easy bleeding/brusining
hematuria
any bleeding
intracranial bleeding (esp in newborn)
65
Q

thiamine/B1 main functions

A

cellular metabolism
creating ATP
TTP cofactor for aerobic metabolism, BCAA catabolism, pentose phosphate pathway

66
Q

TPP

A

thiamine pyrophosphate

67
Q

TPP is a cofactor for which reactions

A

pyruvate dehydrogenase (links glycolysis and TCA cycle)

alpha ketoglutarate dehydrogenase (TCA cycle)

branched chain ketoacid dehydrogenase (BCAA catabolism)

transketolase rxn (PPP)

(transfers active aldehyde group)

68
Q

B1/thiamine def causes

A

inadequate dietary intake (unenriched white rice; common)

alcoholics (reduces absorption)

69
Q

B1/thiamine def progressions/sx

A

wet beriberi (dilated cardiomyopathy, high output HF, edema)

dry beriberi (pain, glove and stocking peripheral neuropathy, muscle weakness)

wernicke encephalopathy (confusion, ataxia, ophthalmoplegia w horizontal nystagmus)

chronic: korsakoff syndrome (irreversible memory loss, false memories confabulation, personality change)

areas of necrosis and hemorrhage in mammillary bodies, damage to ant and dorsomedial nuclei of thalamus (relay station of brain)

70
Q

B2/riboflavin has important roles in

A

aerobic metabolism

making ATP

71
Q

B2/riboflavin is a precursor for

A

mitochondrial electron carriers FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide)

72
Q

B2/riboflavin absorption

A

first absorbed in prox small intestine > liver to be phosphorylated to make FMN (I) and FAD (II) for ETC

73
Q

B2/riboflavin def causes

A 
inadequate dietary intake (common)
malnutrition
chronic alcoholism
liver disease
malabsorption
74
Q

B2/riboflavin sources

A

eggs, animal products, dairy, green leavy veg, enriched cereals

NPLEX I 2024 (23 decks)

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