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IHN: Biochemistry 2 > Quiz 5: Iodine > Flashcards

Quiz 5: Iodine Flashcards

1
Q

Iodine is an __ element

A

Iodine is an ultratrace element

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2
Q

iodine deficiency disorder (IDD) is the leading cause of __

A

iodine deficiency disorder (IDD) is the leading cause of mental development disorders in young children

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3
Q

iodine deficiency promotes

A
  1. impaired cognitive development (mild –> mental retardation (cretinism))
  2. stunted growth
  3. poor school performance
  4. reduced work capacity
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4
Q

iodine deficiency also causes

A

stillbirth
miscarriage
physical impairment
thyroid dysfunction

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5
Q

biological form of iodine

A

I-

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6
Q

what is iodine a component of

A

tri-iodothyonine (T3)
thyroxine (T4)

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7
Q

main way to meet iodine requirements

A

iodized salt

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8
Q

iodine abundance in __ is varied

A

iodine abundance in soil is varied

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9
Q

when is there increased iodine RDA

A

infants
pregnancy
lactation
with age

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10
Q

A 50% increase in maternal __ is needed to maintain maternal __ and transfer __ to fetus

A

A 50% increase in maternal T4 is needed to maintain maternal euthyroidism and transfer thyroid hormone to fetus

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11
Q

why is iodine requirement increased during pregnancy? (2)

A
  1. iodine needs to be transferred to the fetus to make fetal thyroid hormones
  2. increased renal iodine clearance
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12
Q

major food source of iodine

A

bread and milk

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13
Q

variable food sources of iodine

A

beans
eggs
meats
fish

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14
Q

fortified sources of iodine

A

iodized salts

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15
Q

goitrogens promote __ which are __

A

goitrogens promote goiters which are enlarged thyroid glands

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16
Q

goitrogen = substances that inhibits __ uptake and or __ and __ release

A

goitrogen = substances that inhibits iodine uptake and or organification and thyroid hormone release

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17
Q

3 chemical goitrogens

A

goitrin
perchlorate
lithium

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18
Q

food sources of goitrogens

A
  1. cruciferous vegetables
  2. cassava
  3. millet
  4. insecticides
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19
Q

iodine toxicity is __ and causes __ issues

A

iodine toxicity is rare and causes thyroid issues

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20
Q

2 chemical food forms of iodine

A
  1. iodide (I-) bound to amino acids
  2. iodate (IO3-) in bread or iodized salts
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21
Q

where is iodine absorbed

A

upper intestine (duodenum and jejunum)

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22
Q

iodine is secreted into

A

gastric lumen

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23
Q

in healthy adults, __% of iodine is absorbed

A

in healthy adults, > 90% of iodine is absorbed

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24
Q

main iodine transporter

A

NIS

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25
Q

NIS is dependent on __
NIS colocalizes with __ in __
NIS is inhibited by high __

A

NIS is dependent on Na
NIS colocalizes with ATPase in small intestine
NIS is inhibited by high I-

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26
Q

where is NIS found?

A

thyroid gland (for uptake)
lactating mammary gland (secretion into milk)
salivary glands and stomach cells (secretion into digestive tract)

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27
Q

NIS absorption steps

A
  1. iodate –> glutathione –> I-
  2. NIS pulls I- in, Na out
  3. NaK ATPase takes Na out, K in
  4. I- crosses cell to blood
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28
Q

70-80% of iodine is stored in __ (100-fold more than in __)
rest in _, _, and __

A

70-80% of iodine is stored in thyroid gland (100-fold more than in plasma)
rest in salivary glands, stomach, and ovary and testis

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29
Q

excretion of iodine is mainly in __(%)
rest in __

A

excretion of iodine is mainly in urine(80-90%)
rest in feces (10-20%)

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30
Q

__ have major mechanism to regulate iodine reabsorption

A

kidneys have major mechanism to regulate iodine reabsorption

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31
Q

synthesis of thyroid hormones steps

A
  1. I- in blood enters basolateral via Na+/I- symporter
  2. I- gose to Pendrin which sends I- out into colloid
  3. ER makes thyroglobulin –> released into follicle colloid by exocytosis
  4. I- –> I0 (oxidation by thyroid peroxidase)
  5. thyroid peroxidase does iodination, then conjugation to make T4
  6. thyroid cell endocytosis thyroid hormones, proteolysis, secretion into blood of T3 and T4
32
Q

thyroid peroxidase function

A

oxidized I- to I0

33
Q

thyroid peroxidase is a __ containing enzyme
SO, __-deficiency leads to impaired __ function (__)

A

thyroid peroxidase is a heme containing enzyme
SO, iron-deficiency leads to impaired thyroid function (hypothyroidism)

34
Q

thyroid hormones in blood are transported by __

A

thyroid hormones in blood are transported by 3 proteins

35
Q

3 proteins that transport thyroid hormones

A
  1. thyroid hormone-binding globulin (lowest capacity, highest affinity)
  2. thyroid hormone pre-albumin (trans-thyretin)
  3. albumin
36
Q

which transporter of thyroid hormones has the lowest capacity and highest affinity

A

thyroid hormone-binding globulin

37
Q

99.9% of plasma T3 and T4 are __ forms

A

99.9% of plasma T3 and T4 are protein-bound forms

38
Q

plasma conc of __ is 50x higher than that of __ but __ is 20-100x more potent

A

plasma conc of T4 is 50x higher than that of T3 but T3 is 20-100x more potent

39
Q

activation of thyroid hormones is done by __ which contain __

A

activation of thyroid hormones is done by iodothyroxine deiodinases (DI) which contain selenium

40
Q

__ activate thyroid hormones
__ inactivate thyroid hormones

A

DI1, DI2 activate thyroid hormones
DI3 inactivate thyroid hormones

41
Q

which is the main activator of T3?

42
Q

locations
DI1
DI2
DI3

A

locations
DI1: thyroid, liver, kidney
DI2: brain, pituitary, muscle, BAT, heart
DI3: cerebral cortex, skin, placenta, pregnant uterus

43
Q

3 deficiencies that magnify effects of inadequate iodine

A

selenium
iron
vitamin A

44
Q

__ are selenium containing enzymes

A

5’-deiodinases are selenium containing enzymes

45
Q

iron is a component of the enzyme __
iron may also bind to T3 __

A

iron is a component of the enzyme thyroperoxidase
iron may also bind to T3 nuclear receptors

46
Q

vit A deficiency reduces iodine __ by __
decreases synthesis of __
decreases coupling of __ residues to form T4

A

vit A deficiency reduces iodine uptake by thyroid glands
decreases synthesis of thyroglobulin
decreases coupling of iodo-tyrosine residues to form T4

47
Q

4 methods to generate metabolites of thyroid hormones

A
  1. glucouronidation (T4)
  2. sulfation (T3)
  3. deamination
  4. decarboxylation
48
Q

all generated metabolitles of iodine are functionally __

A

all generated metabolitles of iodine are functionally inactive

49
Q

TRH =
TSH =

A

TRH = thyrotropin releasing hormone
TSH = thyroid stimulating hormone

50
Q

thyroid hormones genes editing

A
  1. binding of T3 activates transcription of target genes
51
Q

No T3 =

A

dozens of proteins sit on TRE
deacetylated histones
no trxn

52
Q

with T3 =

A

T3 binds receptor, induces removal of co-repressor complex
T3 recruits histone acetylases –> relaxes DNA –> trxn

53
Q

hypothalamus releases __ to target pituitary
pituitary releases __ to target thyroid
T3+T4 in circulation go to (4)

A

hypothalamus releases TRH to target pituitary
pituitary releases TSH to target thyroid
T3+T4 in circulation go to heart, liver, kidney, tissues

54
Q

high thyroid hormone in circulation inhibits

A

hypothalamus release of TRH
pituitary release of TSH

55
Q

physiological function of thyroid hormones (3)

A
  1. regulation of basal metabolic rate
  2. regulation of macronutrient metabolism
  3. regulate growth and development
56
Q

iodine regulates basal metabolic rate by effecting 2 types of processes

A
  1. energy-producing
  2. energy-consuming
57
Q

iodine and basal metabolic rate
T3 increases __ consumption

A

iodine and basal metabolic rate
T3 increases oxygen consumption

58
Q

iodine energy producing processes that are impacted

A
  1. induce components of ETC
  2. increased activity of ADP translocator into mitochondria
  3. increased mitochondrial membrane area
59
Q

energy consuming processes

A
  1. increased heart rate
  2. increased cell membrane NaK ATPase
60
Q

how does iodine regulate macronutrient metabolism

A

T3 regulates metabolism of ALL macronutrients

61
Q

T3 and carb metabolism

A
  1. increased glycolysis and gluconeogenesis
  2. increased glycogenolysis
62
Q

T3 and lipid metabolism

A
  1. increased synthesis of fatty acids and cholesterol
  2. increased lipolysis and FA ox
  3. increased biliary excretion: reduces blood cholesterol
63
Q

hypothyroidism patients sometimes have __ cholesterol bc T3 is needed for __

A

hypothyroidism patients sometimes have low cholesterol bc T3 is needed for cholesterol synthesis

64
Q

T3 and protein synthesis

A
  1. increased protein synthesis in skeletal musc;e and heart
  2. increased skeletal muscle protein turnover
65
Q

iodine and growth and development

A

T3 modulates brain development and body growth

66
Q

T3 and brain devleopment

A
  1. neuronal axon growth, synaptogenesis
  2. fetal and maternal T3 supply are essential
67
Q

iodine and body growth

A

T3 controls secretion and receptor activation of GH + IGF-1

68
Q

4 ways to assess iodine status

A
  1. serum T3, T4, TSH (highly sensitive for infants and those at risk)
  2. serum thyroglobulin (use with other tests)
  3. urinary iodine (suggests mild insufficiency)
  4. thyroid gland size (uniform enlargement = poor iodine intake)
69
Q

at risk for iodine deficiency

A
  1. pregnant
  2. low I- intake, high goitrogen intake
  3. ppl who don’t use iodized salts
  4. ppl in regions with iodine-deficient soils
70
Q

main sign of iodine deficiency is __ due to __

A

main sign of iodine deficiency is goiter due to thyroid hyperplasia

71
Q

iodine deficiency prevention

A
  1. iodination of salt
  2. potassium iodide or potassium iodate
  3. milk (UK) or oil (Africa)
72
Q

severe iodine deficiency =

73
Q

neurological alterations due to fetal iodine deficiency are

A

irreversible

74
Q

neurological symptoms of cretinism

A

mental retardation
deaf mutism
paralysis

75
Q

__ worsens cretinism symptoms

A

selenium worsens cretinism symptoms

IHN: Biochemistry 2 (38 decks)

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