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HUNT 241 > Lecture 5 - Zinc > Flashcards

Lecture 5 - Zinc Flashcards

1
Q

what are food sources of zinc

A
  • dairy (because we consume large amounts)
  • oysters and seafood
  • meat and poultry
  • organ meats like liver and kidney (found in pate and stuff)
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2
Q

what factors affect zinc bioavailability

A
  • host related factors
  • enhancers and inhibitors in meal
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3
Q

when is zinc absorption enhanced

A

zinc absorption is enhanced during pregnancy

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4
Q

in terms of zinc bioavailability what are enhancers

A
  • meat
  • fish
  • poultry

animal protein in general are good examples of zinc absorption enhancers

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5
Q

in terms of zinc bioavailability what are inhibitord

A
  • if you are taking high doses of iron this will inhibit zinc absorption, especially if supplement is taken between meals
  • phytate
  • combination of phytate and calcium = together this even more inhibitory
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6
Q

what is phytate

A

the molecule that the way in which a plant can store phosphate groups that it will need in order to germinate

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7
Q

what contains phytate

A

anything that could germinate (seeds, nuts, wholegrains, legumes, brown rice)

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8
Q

what does phytate do to zinc

A

very powerful inhibitor

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9
Q

what is the structure of phytate

A

6 carbon ring structure = each has a phosphate attached to it

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10
Q

what is the phytate ring structure similar to

A

similar to glucose (also 6 carbon ring, but one of them is oxygen in the ring)

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11
Q

how is phytate formed

A

glucose is converted to inositol and the groups are replaced with phosphate groups attached

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12
Q

what are some inositol phosphates

A

IP6 and IP4

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13
Q

is IP6 inhibitory or not

A

powerfully inhibitory

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14
Q

why does phytate store phosphate for plants

A

so the plant has easy ways to take the phosphate off and use them

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15
Q

what can you do to food to change it from IP6 to IP4

A

germinate the food, use fermentation also canning foods

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16
Q

what kind of ion is zinc and why does link to phytate

A

divalent positively charged ion = Zn2+

  • binds nicely to the two oxygen on the phytate
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17
Q

where is zinc absorbed

A

proximal small intestine

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18
Q

what are the two mechanisms for zinc absorption

A
  • carrier mediated transport (ZIP4)
  • diffusion (at high doses e.g supplements)
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19
Q

inside cells zinc is either … or ….

A
  • used (enzymes etc)
  • stored (part of meallothionein, or in vesicles, or trans-golgi network)
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20
Q

zinc is transported across basolateral membrane by

A

ZnT1

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21
Q

what does zinc bind to for transport

A
  • albumin
  • transferrin
22
Q

if you don’t absorb all zinc what will happen with it

A

it will be excreted

23
Q

main function of zinc

A

> 200 zinc dependent enzyme

24
Q

how is zinc related to enzymes

A
  • stabilises protein structure by binding to amino cid residues
  • participates in reaction at active site
25
Q

other zinc functions

A
  • gene expression (zinc fingers)
  • tissue and cell growth (regulate protein synthesis)
  • cell membrane integrity
  • cell replication
  • bone formation
  • immune function
  • associated with insulin
  • taste acuity
26
Q

what are zinc fingers used by

A

1,000s of proteins

27
Q

what is the structure of zinc fingers

A

2 Cys and 2 His close together in protein chain > + zinc > protein folds tightly around it

forms a stable structure

28
Q

depending on the function of the particular protein what influence can zinc fingers have

A

enhance or repress gene transcription

29
Q

what is metallothionein

A

small cytoplasmic proteins

30
Q

what is metallothionein rich in

A

cysteine rich - bind up to 7 zinc ions at a time

31
Q

what are the functions of metallothionein

A
  • store zinc (high binding affinity for zinc)
  • zinc transporter within cell
  • cell signalling (especially within and between nerve cells)
  • protect against oxidative stress
32
Q

when and what were the first cases of zinc deficiency reported

A

1960’s in middle east = male adolescent “dwarfs”

33
Q

what were the clinical features of the first zinc reported zinc deficiencies

A
  • stunting = short for their age
  • little or no secondary sexual development
34
Q

what kind of disorder is acrodermatitis enteropathica

A
  • autosomal recessive disorder (need the mutation from both parents)
35
Q

what is acrodermatitis enteropathica caused by and what is the mutation that causes this

A

defective zinc absorption in small intestine

mutation of a gene that codes ZIP4 transporter on enterocytes

36
Q

what are the symptoms of acrodermatitis enteropathica

A

diarrhoea,

alopecia,

dermatitis around the mouth, nostrils, eyes and on palms and soles

poor immune function

delayed healing

37
Q

what are the inadequate dietary intake reasons for zinc deficiency

A
  • low energy intake
  • poor bioavailability
  • environment - low soil zinc
38
Q

what are the high physiological requirement reasons for zinc deficiency

A
  • growth
  • pregnancy
  • infection = immune function
39
Q

what are the excessive losses reasons for zinc deficiency

A
  • diarrhoea
  • surgery, burns
  • excessive alcohol consumption
40
Q

impacts of zinc deficiency of impaired growth

A
  • infancy = poor weight gain
  • children = poor linear growth
41
Q

impacts of zinc deficiency of impaired immune competence

A
  • increased morbidity : diarrhoea, pneumonia
  • increased mortality
42
Q

what are the groups at risk of zinc deficiency

A
  • infants, toddlers and young children
  • adolescents
  • pregnant or lactating women
  • “older people”
  • vegetarians, vegans
  • low socio economic status
  • prolonged diarrhoea
43
Q

what are the effects of zinc toxicity

A
  • metallic taste in mouth
  • nausea
  • gastric distress
  • may be fatal
44
Q

intakes above the upper level of zinc lead to what

A

reduced copper status

45
Q

what are extremely high doses of zinc

A

> 1g zinc/day

46
Q

what are intakes above the upper level of zinc

A

> 40mg/day

47
Q

what does matallothionine preferentially bind to

A

prefers to bind to copper over zinc

48
Q

how does increased zinc lead to decreased copper

A

Zn upregulates the production of metallothionine, this will bind to copper if it is available and then it is stuck in storage and the copper won’t be absorbed into the bloodstream

49
Q

what are the zinc recomendations for adult men

A

RDI : 14mg/day

EAR : 12mg/day

50
Q

what are the zinc recomendations for adult women

A

RDI : 8 mg/day

EAR : 6.5 mg/day

51
Q

what is the upper level of intake for zinc

A

40mg/day

HUNT 241 (19 decks)

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