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Endocrinology & Reproduction > Thyroid hormones and energy homeostasis > Flashcards

Thyroid hormones and energy homeostasis Flashcards

(69 cards)

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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
what inhibits TSH secretion
active TH
26
can TH diffuse across plasma membrane
yes
27
where are thyroid hormone receptors found
located in the nucleus
28
what happens upon binding to thyroid hormone receptor
TH bind to THR which allows receptor to bind to specific DNA sequence
29
what does thyroid hormone receptor require
heterodimer with RXR transcription of specific genes
30
net results of Thyroid hormone receptors
enhanced synthesis of specific proteins
31
thyroid hormones receptors are a __ repsonse
slow
32
main actions of TH
- growth & development - increased oxygen consumption of tissues leading to increased BMR & heat production - increased response to catecholamines in CV - increased NS excitabilty
33
when are TH needed for growth
mainly immediately after birth
34
how does TH increase oxgen consumption of tissues
increased oxidative phosphorylation
35
what does increased responsiveness to catecholamines in CV do
increases HR and BP
36
proof that T3 is effecting CNS
when given to animals in excess during short days, they will increase their body mass to that of long days
37
important roles of T3/4 in humans
increasing BMR and thermogenesis
38
how does TH set BMR
- increases mitochondiral oxidation - increases plasma membrane Na/K ATPase acitivty - regualtes expression of metabolic enzymes - regulates seasonal chages in body mass in mammals
39
how does TH regulate body temperature
- 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
what converts white fat to brown fat
TH
41
what happens when fat is converted from white to brown
increases the pool of cells availble for thermogenesis
42
hypothyroidism
thyroid failure, congenital or later in life
43
when is hypothyroidism fatal
when congenital
44
how to prevent death from congential hypothyroidism
- neonatal screening | - treat with TH ASAP after birth
45
TH are an absolute requirement for
normal growth and development
46
absence of TH causes
- severe growth retardation - bone elonagtion - underdeveloped CNS
47
T3/T4 is permissive for the effects of what other hormones
Growth hormone, and IGF1
48
thyroid insufficiency in infancy =
cretinism
49
cretinism caused by
thryroid insufficiency in infancy
50
what causes thyroid insufficiency in infancy
genetic recessive deficiency, uncommon today | insufficinet iodine in diet, places of war
51
hypothyroidism aquired in later life is common in
middle aged women
52
hasimotos thyroiditis
autoimmune destruction of the thyroid
53
autoimmune destruction of the thyroid
hasimotos thyroiditis
54
hw does hypothyroidism occur in middle aged women
- 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
treatment of hypothyroidism aquired in later life
oral T3.T4 replacement
56
treaatment or lack of iodine in diet
iodinised salt
57
symptoms of hypothyroidism
- low BMR - weight gain - cold sensitivity - deficient growth - slow CNS - decreased cardiac activtiy
58
- low BMR - weight gain - cold sensitivity - deficient growth - slow CNS - decreased cardiac activtiy symptoms of
hypothyroidism
59
anatomical effects of hypothyroidism
- 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
who needs to conusme more iodine
pregnant and lactating women
61
normal iodine recommendatios
100 microgram/l
62
pregnancy and lactation iodine recommendations
250 microgram/l
63
hypertyroidism causes what disease
Grave's disease
64
Grave's disease
hyperthyroidism
65
what causes Graves disease
autoimmune disease with anti bodies stimulating thyroid to secrete T3 and T4 Agonist that binds to receptor to mimic effects of TSH
66
effects of hyperthyroidism
- increased BMR - weight loss - heat sensitivity - increased cardiac activity - hyperactive NS - toxic goitre growth
67
what cuases toxic thyroid goitre growth
hyperthyroidism
68
difference between thyroid goitre in hyper and hypothyroidism
hyper is toxic because TSH receptor is switched on and so T3 and T4 are still being produced
69
treatment of hyperthyroidism
pharmacological blocking of peroxidase to block synthesis of T3 and T4

Endocrinology & Reproduction (15 decks)

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