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Diabetes and Endocrine - Physiology > The Thyroid Gland > Flashcards

The Thyroid Gland Flashcards

1
Q

vertebral extent of thyroid

A

C5-T1

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2
Q

the two thyroid hormones

A

T3 (triiodothyronine) and T4 (thyroxine)

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3
Q

what is contained in the follicles of teh thyroid

A

colloid

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4
Q

what is colloid

A

a glycoprotein containing supply of thyroid hormones and thyroglobulin

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5
Q

2 cells types of thyroid

A

clear cells and follicular cells

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6
Q

what cells surround the colloid

A

follicular

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7
Q

what do clear cells do

A

secrete calcitonin

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8
Q

describe the structure of the thyroid gland

A

follicles filled with colloid with clear cells and capillary interspersed between them, all enclosed in a connective tissue capsule

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9
Q

what do follicular cells do

A

they secrete thyroglobulin proteins and enzymes which make TH

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10
Q

what amino acid forms with iodide to make TH and where does it happen

A

tyrosine in the colloid

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11
Q

how does iodide get into colloid

A

from diet. absorbed into plasma then to follicular cells by coupling to Na+. it is then transported into colloid by pendrin transporter

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12
Q

what is MIT

A

one iodine and one tyrosine (M for mono)

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13
Q

what is DIT

A

two iodine and one tyrosine (D for di)

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14
Q

what combination of MIT and DIT makes T3

A

1 MIT + 1 DIT = T3 (3 iodines)

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15
Q

what combination of MIT and DIT makes T4

A

2 DIT = T4 (4 iodines)

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16
Q

what enzyme secreted by follicular cells catalyses

A

thyroid peroxidase

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17
Q

what stimulates TH release

A

TSH

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18
Q

how is TH released from colloid to plasma

A

endocytosed into follicular cells –> thyroglobulin cut off –> cross cell membrane into plasma

19
Q

how is TH bound in colloid

A

attached to thyroglobulin

20
Q

TH is lipid/water soluble

A

lipid soluble

21
Q

what is TBG

A

thyroxine binding globulin, binds to TH in plasma

22
Q

which TH has a longer half life

A

T4, 6 days compared to 1, its because TBG has a greater affinity for it over T3

23
Q

what proportion of circulating TH is protein bound

A

99.8%

24
Q

which TH binds to more intracellular receptors

A

T3, despite having shorter life and being far less abundant. cell receptors have a greater affinity for it

25
Q

what action does T4 undergo due to T3’s greater receptor affintiy

A

it get deiodinased in plasma and cells

26
Q

stimuli of TRH release

A

cold, exercise and pregnancy

27
Q

action of TRH

A

TSH release

28
Q

action of TSH

A

TH release

29
Q

what class of hormones that cortisol belongs to inhibits TSH and T4–>T3 conversion

A

glucocorticoids

30
Q

inhibitory action of somatostatin (GHIH)

A

inhibits TSH (makes sense because GHIH inhibits GH and GH need TH permissive effects)

31
Q

effects of TH on metabolism

A

increases metabolic rate and creates heat

32
Q

effect of TH on liver

A

increases hepatic gluconeogenesis

33
Q

why is TH not a glucose counter regulatory hormone

A

although it raises gluconeogenesis it has no effect on insulin so BG stays the same

34
Q

effect of TH on protein and fat

A

proteolysis and lipolysis

35
Q

effect of TH on GH

A

permissive, without it stunted growth

36
Q

2 causes of hyperthyroidism

A

graves disease and a thyroid tumour

37
Q

what happens in graves disease to produce hyperthyroidism

A

antibodies mimic TSH at anterior pituitary and continually stimulates TH release. produces negative feedback on TSH but antiboidies keep on stimulating anyway. Thyroid gland gets hyperplastic (big)

38
Q

given the actions of TH what would you expect in hyperthyroidism presentation

A

proteolysis/lipolysis –> thin, weak, wasting
increased metabolism –> weight loss, heat intolerance?

also get exaggerated reflexes, tachycardia, high CO and cardiac failure!

39
Q

why does hyperthyroidism cause heart problems

A

TH is permissive to epinephrine so b receptors very stimulated

40
Q

causes of hypothyroidism

A

hashimoto’s disease, iodine deficiency and idiopathic

41
Q

what happens in hashimoto’s disease

A

there is an autoimmune attack on the thyroid gland –> reduced TH production

42
Q

what would you expect of a hypothroidism presentation

A

decreased metabolic –> weight gain, cold intolerance

permissive to epinephrine –> reduced CV function

Nervous system –> slow speech, reduced reflexes

more general –> fatigue, brittle nails, thin skin

43
Q

what is meant by goitre

A

thyroid enlargement

Diabetes and Endocrine - Physiology (10 decks)

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