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Endocrinology Y2 > Hypothyroidism > Flashcards

Hypothyroidism Flashcards

1
Q

Which is the active and inactive thyroid hormone

A

T4 is inactive, T3 is active.

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2
Q

What does T3 basically control

A

T3 controls basal metabolic rate (body temperature

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3
Q

Describe the hypothalamo-pituitary-thyroid axis inhibitions/stimulations

A

TSH switches on the follicular cells in the thyroid gland and you release thyroxine into your blood stream. T4/T3 has a negative feedback on the pituitary and hypothalamus so level of TRH and TSH goes down as thyroxine goes up.

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4
Q

What is thyroxine

A

T4

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5
Q

What stimulates TSH production

A

The hypothalamus secretes TRH which stimulates the pituitary to make TSH.

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6
Q

What does TSH do molecularly

A

TSH travels to the thyroid in the blood and tells the thyroid to turn on the trapping of iodide in the blood from the diet.

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7
Q

Describe the synthesis of thyroxine

A

The hypothalamus secretes TRH which stimulates the pituitary to make TSH. TSH travels to the thyroid in the blood and tells the thyroid to turn on the trapping of iodide in the blood from the diet. The iodide goes into the thyroid follicle cells and is converted to iodine – after this it binds to tyrosine which then converts it to thyroxine.

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8
Q

What cells make thyroxine

A

follicular cells

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9
Q

How long is our store of thyroxine

A

A month

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10
Q

usual reason for thyroid failure?

A

due to autoimmune damage to the thyroid.

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11
Q

What reaction converts T4 to T3

A

deiodination by deiodinase enzymes

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12
Q

Proportions of circulating T3 from deiodination vs direct thyroid synthesis?

A

80% from deiodination of T4

20% from direct thyroidal secretion

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13
Q

What is used to treat hypothyroidism

A

Thyroxine usually given as a salt LEVOTHYROXINE SODIUM; thyroxine sodium; thyroxine; tetraiodothyronine; T4

and sometimes Liothyronine sodium (T3)

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14
Q

What causes primary hypothyroidism

A

autoimmune, iatrogenic Post-thyroidectomy or post-radioactive iodine

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15
Q

What causes secondary hypothyroidism

A

pituitary tumour, post-pituitary surgery or radiotherapy

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16
Q

RoA of levothyroxine sodium?

A

Oral

17
Q

What do you use to guide levothyroxine sodium dose in primary hypothyroidism

A
  • TSH levels
18
Q

What do you use to guide levothyroxine sodium dose in secondary hypothyroidism

A
  • TSH low due to anterior pituitary failure Can’t use TSH to guide dose Aim for fT4 middle of reference range
19
Q

What is administered in primary hypothyroidism

A

LEVOTHYROXINE SODIUM

20
Q

What is administered in secondary hypothyroidism

A

LEVOTHYROXINE SODIUM

21
Q

When is LEVOTHYROXINE SODIUM used

A

primary and secondary hypothyroidism

22
Q

When is LIOTHYRONINE used and why

A

Myxoedema coma as it is faster and more potent

23
Q

RoA of LIOTHYRONINE

A

IV

24
Q

Adverse effects of thyroid hormone replacement therapy is usually associated with…

A

low/suppressed TSH

25
Q

Side effects of thyroid hormone replacement therapy? (4)

A
  • SKELETAL Increased bone turnover, reduction in bone mineral density, risk of osteoporosis
  • CARDIAC Tachycardia, risk of dysrhythmia- particularly atrial fibrillation
  • METABOLIC Increased energy expenditure, weight loss
  • INCREASED BETA-ADRENERGIC SENSITIVITY Tremor, nervousness
26
Q

Where is circulating thyroxine/thyronine found?

A

Plasma proteins, mainly thyroxine binding globulin TBG

27
Q

What must be bore in mind when administering thyroxine/thyronine re. protein binding

A
  • Plasma binding proteins increase in PREGNANCY and on prolongued treatment with OESTROGENS or PHENOTHIAZINES
  • TBG falls with malnutrition, liver disease and certain drug treaments
  • Certain co-administered drugs (e.g. phenytoin, salicylates) compete for protein binding sites

meaning there will be more bioactive/unbound thyroxine/thyronine

28
Q

Symptoms of hypothyroidism? (7)

A
  • Deepening voice
  • Depression and tiredness
  • Cold intolerance
  • Weight gain with reduced appetite
  • Constipation
  • Bradycardia
  • Eventual myxoedema coma
29
Q

hypothyroidism will eventually lead to…

A

myxoedema coma

30
Q

What is hypothyroidism known as

A

Myxoedema

Endocrinology Y2 (18 decks)

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