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bioregulatory systems 🦠 > thyroid gland > Flashcards

thyroid gland Flashcards

1
Q

how many lobes is the thyroid gland made up of

A

2

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2
Q

what is the middle part of the thyroid gland called

A

the isthmus

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3
Q

what are the cells of the thyroid gland called

A

follicular cells
have colloid in the middle
and parafollicular

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4
Q

what is embedded in the thyroid gland

A

parathyroid glands (2 on each lobe - superior and inferior parathyroid glands)

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5
Q

what runs close to the thyroid gland

A

left recurrent laryngeal nerve (supplies vocal chords)

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6
Q

what does the parathyroid gland do

A

calcium metabolism

hypoparathyroidism

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7
Q

what is the embryology of the thyroid gland

A 
midline outpouching from the floor of pharynx (originates from base of tongue)
development of thyroglossal duct 
divides into 2 lobes 
duct disappears leaving foramen caecum
final position by week 7 
thyroid gland then develops
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8
Q

what is thyroid agenesis

A

no thyroid gland

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9
Q

STEPS for production of T3 and T4

A

1) TSH binds to TSH-R and sets off a series of events
- activates Na-I transporter allowing I to enter cell
- activates TG (thyroglobulin) production
- activation of TPO enzyme
2) TG (a prohormone) enters the colloid
3) TPO (enzyme) enters colloid and catalyses
- iodination with hydrogen peroxide
- coupling reaction
4) TG converted to MIT and DIT (monoiodotyrosine and diiodotyrosine)
5) forms T3 and T4

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10
Q

what does an MIT and DIT make

A

T3

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11
Q

what do 2 DITs make

A

T4 (thyroxine)

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12
Q

what is the main product of the thyroid gland

A

thyroxine T4

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13
Q

what happens to T4

A

it is deiodinated to T3 (triiodothyronine) its bioactive form in target tissues
it can also be deiodinated in a different position to produce reverse T3 (inactive)

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14
Q

what does a healthy adult thyroid gland secrete

A

both T3 and T4

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15
Q

what is T4

A

the bubble tea shop duh
jk
it is a prohormone converted to T3 by deiodinase enzyme into T3

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16
Q

what are the percentages for how T3 is made

A

80% by deiodination of T4
and 20% from direct thyoridal secretion
T3 provides almost all the thyroid hormone activity in target cells

17
Q

how is T3 transported in the blood

A

mostly bound to plasma proteins when entering circulation
- thyroid binding globulin TBG (70-80%)
- albumin (10-15%)
- prealbumin (aka. transthyretin)
only 0.05% T4 and 0.5% T3 is unbound (bioactive components)

18
Q

what does T3 do inside target cells

A

enters the nucleus and directly alters gene expression

19
Q

what is thyroid hormone essential for

A

foetal growth and development esp the CNS

20
Q

what can untreated congenital hypothyroidism be called

A

cretinism (unable to make own thyroid hormone)

21
Q

what is measured in newborn infants during the heel prick test on day 5 and what can it be a sign of

A

TSH

can be a sign of congenital hypothyroidism

22
Q

what does thyroid hormone do

A

increases basal metabolic rate (amount of energy each cell requires to function)
protein, carbohydrate and fat metabolism
potentiate actions of catecholamines (eg tachycardia and lipolysis)
effects on GI, CNS and reproductive system (fertility)

23
Q

half life of T4 and T3

A

T4 ~ 7-9 days

T3 ~ 2 days

24
Q

summary of thyroid hormone actions

A

thyroid hormone binds to nuclear receptor > synthesis of new proteins > leads to
growth - bone maturation
CNS - maturation of CNS
BMS - ^ Na+/K+ ATPase, ^O2 consumption, ^heat production, ^BMR
metabolism - ^glucose absorption, ^glycogenolysis, gluconeogenesis, ^lipolysis, ^protein degradation and synthesis
cardiovascular - ^cardiac output

25
Q

control of thyroid hormone production (what inhibits anterior pituitary production of TSH)

A

somatostatin

there is also negative feedback to switch off TSH production when there is too much T3 and T4 produced

26
Q

what is primary hypothyroidism

A

autoimmune damage to the thyroid gland
thyroxine/T4 level decline
TSH levels climb

27
Q

what are the commonest forms of autoimmune thyroid disease

A

Hashimotos thyroiditis
Grave’s disease (tho normally associated with hyper)
the presence of 1 autoimmune disease increases the risk of others
presence of autoantibodies damaging thyroid

28
Q

symptoms and signs of hypothyroidism

A 
deepening voice
depression and tiredness
cold intolerance
weight gain with reduced appetite
constipation
bradycardia 
eventual myxoedema coma
29
Q

pharmacology and therapeutics : levothyroxine

indications of hypo and hyperthyroidism

A

hypo - inability to make thyroid hormone

hyper - blocking and replacement regimen

30
Q

dosing for levothyroxine is adjusted to?

A

according to TSH (aim to get in normal range) and low T4 and high TSH if hypothyroidism due to negative feedback

31
Q

most common dose of levothyroxine

A

100 micrograms

32
Q

most common way of administering levothyroxine

A

orally

33
Q

when do you need to give levothyroxine via IVF

A

myxoedema coma

34
Q

what are some potential complications with levothyroxine use

A

weight loss
headaches
heart attack
rapid HR

35
Q

what are some symptoms of toxicity associated with combined thyroid hormone replacement

A

palpitations, tremor, anxiety

often combination treatment suppresses TSH

36
Q

what is hyperthyroidism

A

thyroid makes too much thyroxine
T4 levels rise
TSH levels drop

37
Q

causes of hyperthyroidism

A

Graves disease - whole gland is smoothly enlarged and whole gland is overactive
toxic multinodular goitre
solitary toxic nodule
which both overproduce T4

38
Q

what is Graves disease

A

an autoimmune disease
antibodies bind to and stimulate TSH receptor in the thyroid gland
smooth goite - no nodules
no negative feedback = continual stimulation
other antibodies bind to muscles behind the eye causing bulging - exopthalamos
other antibodies stimulate growth of soft tissue of shins - pretibial myxoedema - thickening of skin on shin

39
Q

signs and symptoms of hyperthyroidism

A 
heat intolerance
weight loss with increased appetite
myopathy
mood swings
diarrhoea
tremor of hands
palpitations
sore eyes
can occur through surgeries

bioregulatory systems 🦠 (54 decks)

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