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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
malabsorptive disorders effect absorption of what vitamins
fat soluble | A, D, E, K
26
vit D def sx
low 25 hydroxy vit D low Ca, low Phos hyper PTH (low ca over long time)
27
bone disorders associated with severe vit D deficiency
rickets | osteomalacia
28
high vitamin D sx
sx of hypercalcemia
29
excess vit D causes
granulomatous disorders
30
retinol common name
vit A
31
folate common name
B9
32
biotin common name
B7
33
pyridoxine common name
B6
34
pantothenic acid common name
B5
35
niacin common name
B3
36
riboflavin common name
B2
37
thiamine common name
B1
38
cobalamin common name
B12
39
vit A precursors/sources
beta-carotenes and retinol esthers (both from dietary sources)
40
retinol absorption, conversion, and storage
retinol absorebd in small intestine > converted into retinol esthers > picked up by chylomicrons > stored in liver stellate cells
41
retinol crosses cell membrane and enters nucleus in what form, to do what
retinoic acid > modify gene transcription
42
vit A main functions
orderly cellular differentiation and maturation | vision
43
vit A vision effects
retinol is part of rhodopsin (light sensitive protein important for photo transduction) > sharpen vision and image
44
causes of vit A deficiency
``` 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
vit A def sx
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
acute vit A toxicity sx
blurry vision vertigo N/V
47
chronic vit A toxicity sx
``` hepatic toxicity and enlargement cheilitis (lip inflammation) arthralgias alopecia hyperkeratosis (dry, thickened skin) pseudotumor cerebri (idiopathic intracranial hypertension ICH) > inc CSF pressure, papilledema) ```
48
vit A derviatives (s/a isotretinoin) contraindications
pregnancy highly teratogenic
49
vit E exists in how many forms
8 tocopherols/tocotrionals
50
most biologically active form of vit E
alpha-tocopherol
51
vit E functions
cell membrane protection via neutralizing free radicals (antioxidant) prevents oxidation of LDL neuroprotection (may slow decline in alzheimers)
52
vit E deficiency causes
``` dietary intake (rare) fat malabsorption (pancreatic insufficiency, cholestatic liver dz, bariatric surgery) genetic: abetalipoproteinemia, AVED (ataxia w vit E def) ```
53
vit E def sx
``` 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
vit E toxicity sx
interferes with vit K metabolsim inc bleeding with warfarin inc risk of hemorrhagic stroke necrotizing enterocolitis in infants
55
vit E high dose indications
age related macular degeneration | NAFLD
56
vit K natural forms
phylloquinone, menaquinone
57
vit K natural forms
phylloquinone, menaquinone
58
main source of vit K
leafy green veggies, gut flora
59
vit K activation
oxidized inactive vit K converted to reduced active vit K via VKOR (vit K epoxide reductase)
60
vit K is a cofactor for
gamma-glutamyl carboxylase (GGC), which catalyzes the post translational modification of the vit K dependent proteins: factors 2, 7, 9, 10, C, S
61
causes of vit K def
``` inadequate dietary intake fat malabsorptive disorders prolonged use of broad spectrum antibiotics (eradicate gut flora that produce vit K) warfarin newborns ```
62
what drug can mimic vit K def sx
warfarin; blocks VKOR which blocks vit K activation
63
reasons why newborns more likely to develop vit K deficiency
breastmilk low in vit K dont have fully developed liver no gut bacteria/sterile guts doesnt cross placenta
64
vit K def sx
``` bleeding diathesis easy bleeding/brusining hematuria any bleeding intracranial bleeding (esp in newborn) ```
65
thiamine/B1 main functions
cellular metabolism creating ATP TTP cofactor for aerobic metabolism, BCAA catabolism, pentose phosphate pathway
66
TPP
thiamine pyrophosphate
67
TPP is a cofactor for which reactions
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
B1/thiamine def causes
inadequate dietary intake (unenriched white rice; common) | alcoholics (reduces absorption)
69
B1/thiamine def progressions/sx
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
B2/riboflavin has important roles in
aerobic metabolism | making ATP
71
B2/riboflavin is a precursor for
mitochondrial electron carriers FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide)
72
B2/riboflavin absorption
first absorbed in prox small intestine > liver to be phosphorylated to make FMN (I) and FAD (II) for ETC
73
B2/riboflavin def causes
``` inadequate dietary intake (common) malnutrition chronic alcoholism liver disease malabsorption ```
74
B2/riboflavin sources
eggs, animal products, dairy, green leavy veg, enriched cereals

NPLEX I 2024 (23 decks)

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