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Endocrinology > thyroid gland > Flashcards

thyroid gland Flashcards

1
Q

position and weight of thyroid?

A

lies across trachea at base pf larynx, ~15-20g

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2
Q

is it palpable?

A

not in health

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3
Q

which are the active forms of thyroid hormones?

A

T3 and T4

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4
Q

T3?

A

triiodothyronine

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5
Q

T4?

A

Thyroxine

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6
Q

2 types of cells present in thyroid w function?

A

C cells - secrete calcitonin

follicular cells - support thyroid hormone synthesis and surround follicles

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7
Q

what are thyroid follicles?

A

spherical structures which walls are made of follicular cells

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8
Q

describe centre of follicle?

A

filled with colloid, a sticky glycoprotein matrix, containing 2-3 months supply of TH

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9
Q

function of follicular cells?

A

manufacture enzymes which make thyroid hormones and thyroglobulin

concentrates iodide

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10
Q

residues abundant on thyroglobulin?

A

tyrosine

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11
Q

how are thyroid hormones formed?

A

iodide and tyrosine are combined in the colloid

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12
Q

how does iodide enter follicular cells?

A

via Na+/I- transporter (symport)

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13
Q

how is iodide transported to the colloid?

A

via pendrin transporter

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14
Q

result of addition of 1 iodine to tyrosine?

A

MIT - monoiodotyrosine

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15
Q

result of adding 2 iodines to tyrosine?

A

DIT - diiodotyrosine

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16
Q

how is T3 formed?

A

MIT + DIT

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17
Q

how is T4 formed?

A

DIT + DIT

18
Q

composition of T3?

A

2 tyrosine + 3 iodines

19
Q

composition of T4?

A

2 tyrosine + 4 iodines

20
Q

function of thyroid perioxidase?

A

catalyse thyroid hormone (T3+4) synthesis

21
Q

solubility of T3+4 and effect of this?

A

lipid-soluble - pass across follicular cell membrane where they bind to plasma protein thyroxine-binding globulin

22
Q

rare cause of disruption to TH balance?

A

mutations to thyroxine-binding globulin

23
Q

effect of TBG’s high affinity for T4?

A

T4 is released slowly into the plasma

24
Q

half-life of T3?

A

~1 day

25
Q

half-life of T4?

A

~6 days

26
Q

% of T3+4 are free to act as inhibitors to TSH and TRH?

A

0.2% - acts via -ve feedback loop

27
Q

is T3/4 more. abundant and by how many times?

A

T4 - x50 more

28
Q

T3 % of binding of thyroid hormones to receptors in cells?

A

90%, despite being far less abundant than T4

29
Q

why does T3 bind more than T4 and what is the result of this?

A

receptors have higher affinity for T3 than T4 - therefore, T3 is x3-5 more physiologically active than T4

30
Q

which can increase TRH secretion from hypothalamus?

A

pregnancy
cold
exercise

31
Q

effect of somatostatin on TSH?

A

inhibitory

32
Q

effect of glucocorticoids on TSH?

A

inhibitory - also inhibits conversion of T4 to T3

33
Q

functions of thyroid hormone?

A

raises metabolic rate and promotes thermogenesis

increase hepatic gluconeogenesis

net increase in proteolysis

net increase in lipolysis

critical for growth (lack of TH results in retarded growth)

brain development in utero

34
Q

result of maternal iodine deficiency?

A

congenital hypothyroidism

35
Q

name 2 causes of hyperthyroidism?

A 
Graves disease (common)
Thyroid adenoma (rare)
36
Q

3 signs of graves disease?

A

hyperplasia -> enlarged thyroid gland

hyperactivity of cells

TSH plasma conc. is very low

37
Q

6 symptoms of hyperthyroidism?

A 
weight loss
heat intolerance
muscle weakness
hyper-excitable reflexes
psychological disturbances
increased HR/contractile force, high output, cardiac failure
38
Q

3 causes of hypothyroidism?

A

Hashimoto’s disease (autoimmune)
dietary deficiency in iodine
idiopathic - related to thyroiditis

39
Q

symptoms of hypothyroidism?

A 
weight gain
cold intolerance 
brittle nails/hair 
thin skin 
slow speech reflexes fatigue
slow heart rate/weaker pulse
40
Q

define goitre?

A

enlargement of thyroid gland due to either hyper/hypo-thyroidism

41
Q

hypo cause of goitre?

A

increased trophic action of TSH on follicular cells

42
Q

hyper cause of goitre?

A

overactivity due to graves disease

Endocrinology (21 decks)

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