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Endocrinology > Lec 8 - Thyroid hormones > Flashcards

Lec 8 - Thyroid hormones Flashcards

1
Q

what are thyroid hormones derived from

A

tyrosine

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2
Q

3 types of thyroid hormones

A

Thyroxine = T4
Triiodothyronine = T3
Reverse T3 = inactive

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3
Q

why does T4 need binding proteins to transoprt it in serum

A

is insoluble

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4
Q

why can liver disease lead to loss of effective t4 transport

A

this is where binding proteins are synthesised

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5
Q

3 types of T4 binding proteins

A
  • albumin
  • transthyretin (ttr)
  • Thyroxine binding protein (TBG)
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6
Q

most abundant t4 binding portein

A

thyroxine binding globulin
70-75%

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7
Q

how much T4 does albumin hold in plasma

A

5-10%

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8
Q

how much t4 does TTR bind (and where does it deliver to)

A

20%
delivers to CNS

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9
Q

where is T4 converted

A

in peripheral tissues

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10
Q

which binding protein has highest affinity for t4

A

TBG

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11
Q

which bindning protein has highest capacity for t4

A

albumin
but since has lowest affinity = holds the least

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12
Q

which of the binding proteins ONLY binds t4 and not t3

A

TTR

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13
Q

what hormone increases TBG

A

oestrogen
which is why in nearly doubles in conc during pregnancy

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14
Q

what lowers concs of TBG

A

corticosteroids
illness
stress
cirrhosis
nephrotic disorders

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15
Q

which transporters move free t4 and t3 into cells

A

MCT8
MCT10
OATP1c1

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16
Q

which enzymes convert T4 to T3

A

iodothyronine deiodinases (DIO)
(1, 2 and 3)

17
Q

which DIO makes the most circulating T3

A

DIO1

18
Q

where is DIO1 predominately found

A

liver
kidney
muscle

19
Q

where is DIO2 found

A

areas of CNS
and
pituitary thyrotropes

20
Q

what kind of T3 does DIO2 make

A

intracellular T3

21
Q

DIO3 function

A

produces reverse T3
- prevents thyroid hormone accessing specific tissues

22
Q

what is the 2 thyroid hormone receptors and where are they

A

TRalpha and TRbeta
- found in nucleus

23
Q

what do TR form a dimer with

A

retinoid X receptor (RXR)

24
Q

where does TR and RXR bind

A

to thyroid resposive element
on DNA
(hard to explain, see onenote)

25
Q

how does T3 affect growth hormone

A

the gene encoding growth hormone is responsive to T3
= increases gene expression

26
Q

in what situation would T3 binding actually lead to gene inhibition

A

in gene coding for expression of alpha and beta subunits of TSH
(mechanism of negative feedback)

27
Q

5 biological actions of thyroid hormone

A
  • control basal metabolic rate
  • growth regulating role
  • foetal development
  • cardiovascular effects
  • musculoskeletal effects
28
Q

3 things thyroid hormone does to affect basal metabolic rate

A
  • increases proteins for tissue growth and maturation
  • increases expression of Na+/K+ ATPase
  • increases mitochondria (stimulating mt replication) and respiratory enzymes
29
Q

what are the effects on cardiac when increased thyroid hormone

A

more O2 needed
to supply increase in metabolism
so cardiac output and ventilation increases

30
Q

what does loss of t4 in foetus lead to

A

irreversible intellectual disability and dwarfism

31
Q

effect of iodine deficiency in foetus

A
  • miscarriage/stillbirth
  • congenital abnormality
32
Q

effect of iodine deficiency in foetus

A

neonatal goiter
neonatal hypothyroidism
intellectual disability

33
Q

iodine decifiency in child/adolecsent

A

subclinical goiter hypothyroidism
impaired mentla funciton
delayed phsyical development

34
Q

what does T3 increase in terms of cardiovascular effects

A
  • cardiac contraction and output
  • heart rate
  • increased O2 supply to tissues
  • inc CO2 removal from tissues
35
Q

3 direct effects of T3 in CV system

A
  • inc myocardial Ca2+ uptake
  • inc expression of alpha-myosin heavy chain and decreased beta
  • increased expression of RYR in SR
36
Q

indirect effects of T3 on CV system

A
  • increased metabolism = inc thermogenesis = vasodilation
  • inc sensitivity to catecholamines
37
Q

how does t3 have musculoskeletory effectsq

A
38
Q
A

Endocrinology (25 decks)

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