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Endocrinology & Reproduction > Thyroid hormones and energy homeostasis > Flashcards

Thyroid hormones and energy homeostasis Flashcards

1
Q

what are thyroid follicles

A

balls of epithelial cells surrounding non-cellular proteinaceous colloid

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2
Q

where are thyroid hormoes stored

A

thyroid folllicles

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3
Q

what are T3 and T4

A

iodinated tyrosine derivates

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4
Q

where are TH synthesised

A

outside the thyroid cells in colloid on a protein template called thyroglobulin

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5
Q

where is the only place in the body that needs iodine

A

thyroglobulin

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6
Q

what is the enzyme that oxidises iodine to its active form iodisine

A

peroxidase

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7
Q

what does peroxidase do

A

actiivates iodine by oxidation

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8
Q

what are iodinated tyrosin resiudes on thyroglobulin called

A

DIT

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9
Q

what is T4

A

two DIT

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10
Q

what happens to T4 once made

A

will stay bound to thyroglobulin and will remain stored in colloid until needed

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11
Q

how does T4 leave colloid

A

diffuses out but not by exocytosis

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12
Q

T4 production is slow or fast

A

slow but effective

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13
Q

what happens to thyroglobulin when T4 is released from colloid

A

lysosomes break down the thyroglobulin

AA are recycle and the T4 diffues into circualtion

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14
Q

what stimuates TSH

A

TRH

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15
Q

what does TRH stimulate

A

TSH

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16
Q

where is TSH released from

A

anterior pituitary

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17
Q

what stimuates T4 release

A

TSH

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18
Q

what hapens to T4 at target cells

A

deiodinated to form T3

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19
Q

where does T3 form

A

at target cells

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20
Q

what does TSH also stimualte

A

growth of thyroid

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21
Q

how does 90% of T4 travel in circualtion

A

bound to TBG in plasma

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22
Q

why does T4 travel bound to TBG

A

to keeo a reserve of T4 incirculation for release when needed

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23
Q

what state is the majority of unbound TH

A

biologically activive, mostly T3

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24
Q

what does unbound TH do

A

biologically active and feeds back to inhibit TSH secretion at level of pituitary and hypothalmus

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25
Q

what inhibits TSH secretion

A

active TH

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26
Q

can TH diffuse across plasma membrane

A

yes

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27
Q

where are thyroid hormone receptors found

A

located in the nucleus

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28
Q

what happens upon binding to thyroid hormone receptor

A

TH bind to THR which allows receptor to bind to specific DNA sequence

29
Q

what does thyroid hormone receptor require

A

heterodimer with RXR transcription of specific genes

30
Q

net results of Thyroid hormone receptors

A

enhanced synthesis of specific proteins

31
Q

thyroid hormones receptors are a __ repsonse

A

slow

32
Q

main actions of TH

A
  • growth & development
  • increased oxygen consumption of tissues leading to increased BMR & heat production
  • increased response to catecholamines in CV
  • increased NS excitabilty
33
Q

when are TH needed for growth

A

mainly immediately after birth

34
Q

how does TH increase oxgen consumption of tissues

A

increased oxidative phosphorylation

35
Q

what does increased responsiveness to catecholamines in CV do

A

increases HR and BP

36
Q

proof that T3 is effecting CNS

A

when given to animals in excess during short days, they will increase their body mass to that of long days

37
Q

important roles of T3/4 in humans

A

increasing BMR and thermogenesis

38
Q

how does TH set BMR

A
  • increases mitochondiral oxidation
  • increases plasma membrane Na/K ATPase acitivty
  • regualtes expression of metabolic enzymes
  • regulates seasonal chages in body mass in mammals
39
Q

how does TH regulate body temperature

A
  • increases expression of UCP-1
  • UCP-1 uncouples ATP synthesis from metabolism to generate heat instead
  • central effect to induce browning of white adipose
  • direct effect on mitochondria in brown fat and skeletal muscle
40
Q

what converts white fat to brown fat

A

TH

41
Q

what happens when fat is converted from white to brown

A

increases the pool of cells availble for thermogenesis

42
Q

hypothyroidism

A

thyroid failure, congenital or later in life

43
Q

when is hypothyroidism fatal

A

when congenital

44
Q

how to prevent death from congential hypothyroidism

A
  • neonatal screening

- treat with TH ASAP after birth

45
Q

TH are an absolute requirement for

A

normal growth and development

46
Q

absence of TH causes

A
  • severe growth retardation
  • bone elonagtion
  • underdeveloped CNS
47
Q

T3/T4 is permissive for the effects of what other hormones

A

Growth hormone, and IGF1

48
Q

thyroid insufficiency in infancy =

A

cretinism

49
Q

cretinism caused by

A

thryroid insufficiency in infancy

50
Q

what causes thyroid insufficiency in infancy

A

genetic recessive deficiency, uncommon today

insufficinet iodine in diet, places of war

51
Q

hypothyroidism aquired in later life is common in

A

middle aged women

52
Q

hasimotos thyroiditis

A

autoimmune destruction of the thyroid

53
Q

autoimmune destruction of the thyroid

A

hasimotos thyroiditis

54
Q

hw does hypothyroidism occur in middle aged women

A
  • post menopause
  • oestrogen drops which reduces prtective effect
  • circualting antibodies attack thyroid perioxidase, thyroglobulin anf or TSH receptors
  • TSH is increased as pituiatry tries to compensate for less T4
55
Q

treatment of hypothyroidism aquired in later life

A

oral T3.T4 replacement

56
Q

treaatment or lack of iodine in diet

A

iodinised salt

57
Q

symptoms of hypothyroidism

A
  • low BMR
  • weight gain
  • cold sensitivity
  • deficient growth
  • slow CNS
  • decreased cardiac activtiy
58
Q
  • low BMR
  • weight gain
  • cold sensitivity
  • deficient growth
  • slow CNS
  • decreased cardiac activtiy
    symptoms of
A

hypothyroidism

59
Q

anatomical effects of hypothyroidism

A
  • lack of T3 and T4 means no inhibitoos of TSH
  • elevated TSH
  • TSH stimulates thyroid growth
  • thyroid goitre forms
  • goitre is not producing TH and is benign but removed
60
Q

who needs to conusme more iodine

A

pregnant and lactating women

61
Q

normal iodine recommendatios

A

100 microgram/l

62
Q

pregnancy and lactation iodine recommendations

A

250 microgram/l

63
Q

hypertyroidism causes what disease

A

Grave’s disease

64
Q

Grave’s disease

A

hyperthyroidism

65
Q

what causes Graves disease

A

autoimmune disease with anti bodies stimulating thyroid to secrete T3 and T4
Agonist that binds to receptor to mimic effects of TSH

66
Q

effects of hyperthyroidism

A
  • increased BMR
  • weight loss
  • heat sensitivity
  • increased cardiac activity
  • hyperactive NS
  • toxic goitre growth
67
Q

what cuases toxic thyroid goitre growth

A

hyperthyroidism

68
Q

difference between thyroid goitre in hyper and hypothyroidism

A

hyper is toxic because TSH receptor is switched on and so T3 and T4 are still being produced

69
Q

treatment of hyperthyroidism

A

pharmacological blocking of peroxidase to block synthesis of T3 and T4

Endocrinology & Reproduction (15 decks)

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