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ELM3 - endocrine > thryoid hormones > Flashcards

thryoid hormones Flashcards

1
Q

What are the 2 thyroid hormones?

A

T3 (triiodothyronine), T4 (thyroxine)

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2
Q

Which thyroid hormone is the more active form?

A

T3

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3
Q

Which hormone acts of the the thyroid gland to trigger T3/T4 release?

A

Thyroid stimulating hormone (TSH)

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4
Q

What are the steps in the production of the thyroid hormones in the thyroid gland?

A
  1. thryoid gland absorbs iodine from the bloodstream
  2. follicular cells synthesise thyroglobulin which is secreted into the colloid
  3. iodine is bound to tyrosine residues on thryoglobulin, forming precursors to T3 and T4.
  4. T3/T4 are formed and stored in thryoid follicles until they are released under the stimulation of TSH
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5
Q

What is the main carrier protein for thyroid hormones?

A

Thyroxine-binding globulin

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6
Q

What is the structure of T4?

A

Contains two DITs, which have a total of 4 iodines

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7
Q

What is the structure of T3?

A

Contains a DIT and MIT, with a total of 3 iodines

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8
Q

What is the relationship between free and bound thryoid hormones in the blood stream?

A

They are in a dynamic equilibrium. The unbound/free fraction is a small percentage but is physiologically active.

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9
Q

What is the receptor binding of T3/T4?

A

They enter cells and bind to nuclear receptors to influence gene expression

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10
Q

What are the metabolic functions of thyroid hormones?

A

Increase basal metabolic rate (raises body temperature), promotes oxygen consumption and energy production

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11
Q

What is the role of thyroid hormones in infants/foetuses?

A

Nervous system development

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12
Q

What are the negative feedback loops for thyroid hormones?

A

T3 and T4 have negative feedback to both the hypothalamus and anterior pituitary, reducing TRH and TSH release respectively

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13
Q

What are the causes of hyperthyroidism?

A

Grave’s disease, toxic nodular goitre, thyroid adenoma, thyroiditis

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14
Q

What is Grave’s disease?

A

An autoimmune disorder where the thyroid gland is stimulated by an abnormal immunoglobulins that have a TSH-like effect on TSH receptors causing excessive T4/T3 release.

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15
Q

What is toxic multinodular goitre?

A

Nodules in the thyroid gland become able to synthesise and secrete T3/T4 independent of TSH receptor stimulation

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16
Q

What is a toxic thyroid adenoma?

A

A benign tumor of the thyroid gland that produces excess T3/T4

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17
Q

What is thyroiditis?

A

Inflammation of the thyroid gland, leading to the release of stored thyroid hormones into the bloodstream.

18
Q

What is T3 thyrotoxicosis?

A

Increased levels of free T3, but normal T4 and low TSH

19
Q

What are the symptoms of hyperthyroidism?

A

Weight loss, increased appetite, anxiety, tachycardia/palpitations, arrhythmias, insomnia, fatigue, exophthalmos, goitre, heat intolerance, excessive sweating

20
Q

What are the results of thyroid function tests in hyperthyroidism?

A

TSH is usually low, while T3/T4 are elevated

21
Q

What are the results of thyroid antibody panels in hyperthyroidism?

A

If caused by Grave’s Disease, will be positive for Thyroid stimulating antibodies

22
Q

What will be the result of a Radioactive Iodine reuptake test in Grave’s disease?

A

High, diffuse uptake

23
Q

What will be the result of a Radioactive Iodine reuptake test in thyroiditis?

A

Diffuse pattern of low uptake

24
Q

What will be the result of a Radioactive Iodine reuptake test in toxic multinodular goitre?

A

Focal uptake in thyroid nodules

25
Q

What will be the result of a Radioactive Iodine reuptake test in toxic adenoma?

A

‘Hot’ nodule - area of increased uptake

26
Q

What investigations can be used to diagnose hyperthyroidism?

A

thyroid function test, thyroid antibody panel, radioactive iodine reuptake test/scan, ultrasound

27
Q

What are the non-pharmacological interventions for hyperthyroidism?

A

full/partial thyroidectomy, Radioactive iodine therapy

28
Q

What are the pharmacological interventions for hyperthyroidism?

A

Anti-thyroid drugs (e.g. carbimazole), Beta-blockers for anxiety/arrhythmia

29
Q

What are the causes of hypothyroidism?

A

Hashimoto’s thyroiditis, Iodine deficiency, thyroidectomy/radioactive iodine therapy, pituitary dysfunction

30
Q

What is Hashimoto’s Thyroiditis?

A

An autoimmune condition that causes the destruction of the thyroid gland

31
Q

What dietary deficiency is associated with hypothyroidism and goitre?

A

Iodine

32
Q

What is primary hypothyroidism?

A

A condition where the thyroid is unable to produce thyroid hormone, despite high levels of TSH

33
Q

What is secondary hypothyroidism?

A

Low thyroid hormone release due to insufficient stimulation from low TSH levels

34
Q

What are some causes of primary hypothyroidism?

A

Hashimoto’s thyroiditis, iodine deficiency, thyroidectomy, drugs

35
Q

What are some causes of secondary hypothyroidism?

A

Lesion/stroke of pituitary gland destroying TSH secreting cells

36
Q

What are the symptoms of hypothyroidism?

A

fatigue, weight gain, reduced appetite, cold intolerance, dry skin, thinning hair, brittle nails, depression, constipation, bradycardia, muscle aches, puffy face, goitre, menstrual irregularities

37
Q

What are the results of thyroid function tests in hypothyroidism?

A

T3/T4 are low. TSH is high in primary, and low in secondary hypothyroidism

38
Q

What are the typical results of a thyroid anti-body panel in hypothyroidism?

A

If hypothyroidism is caused by Hashimoto’s will likely to positive for anti-thyroid peroxidase antibodies

39
Q

What is the appearance of a radioactive iodine reputake scan in primary hypothyroidism?

A

There will be diffuse, low uptake

40
Q

What is the appearance of a radioactive iodine reputake scan with a non-secreting thyroid nodule?

A

‘Cold’ nodule - nodule will have less uptake than the rest of the thyroid

41
Q

What are the treatments for hypothyroidism?

A

hormone replacement therapy (levothyroxine), iodine supplementation

ELM3 - endocrine (10 decks)

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