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PHPY 305 > Thyroid Disorders > Flashcards

Thyroid Disorders Flashcards

1
Q

Thyroid physiology

A
  • Thyrotropin releasing hormone (TRH) from the hypothalamus stimulates pituitary to release Thyroid stimulating hormone (TSH)
  • Thyroid stimulating hormone from the pituitary then stimulates the thyroid to release thyroid hormone
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2
Q

Regulation of TH release

A
  • TH exhibits negative feedback inhibition of TSH

- Similarly TSH inhibits release of TRH

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3
Q

Role of Thyroid Peroxidase

A
  • adds iodine to tyrosine and facilitates coupling of MIT + DIT
  • converts iodide into iodine
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4
Q

Monoiodotyrosine (MIT) and Diiodotyrosine (DIT)

A

MIT and DIT combine to form T3

DIT and DIT combine to form T4

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5
Q

Thyroid Hormone conversions

A

T4 is converted to T3 in the periphery
T3 is the more active for of the two
Some T3 is converted to reverse T3 (rT3) which is inactive

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6
Q

Thyroid Hormone receptors and effects

A
  • two types of receptors: TRalpha and TRbeta
  • Once TH binds, the TR can combine in different ways: combine with each other to form homodimers, combine with other transcription factors to form heterodimers, either way promotes gene expression
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7
Q

TH functions

A

On growth/development of the CNS: congenital deficiency can result in developmental delays

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8
Q

Excess TH can cause..

A 
Excess energy (anxiety)
Heat intolerance 
Weight loss
Tachycardia
Sweating
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9
Q

Low TH can cause..

A 
Low energy 
Cold intolerance 
Weight gain
Bradycardia 
Dry skin
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10
Q

Thyroid diseases

A

Graves’ disease

Hashimoto’s Thyroiditis

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11
Q

Grave’s disease

A
  • Thyroid stimulating Immunoglobulin (TsIg) is produced
  • TsIg binds to the TSH receptor (TSH-R), stimulates the thyroid
  • Result: Hyperthyroidism
  • treated with drugs that reduce TH release
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12
Q

Hashimoto’s Thyroiditis

A
  • gradual inflammatory destruction of thyroid gland
  • after initial flare of TH hormone release, TH becomes low
  • Result: Hypothyroidism
  • treated with TH supplementation
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13
Q

Hypothyroidism treatment

A

Treated with thyroid supplementation

  • Levothyroxine
  • Liothyronine
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14
Q

Levothyroxine function

A
  • converted to T3 in body
  • preferred option for Hypothyroidism
  • well established efficacy/safety
  • Long half-life (7 days) so less fluctuation in T3 levels
  • T4 may provide a ‘reservoir’ of TH that can be converted to T3 when needed
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15
Q

Levothyroxine administration

A
  • a number of substances interfere with T4 absorption
  • common: supplements (calcium, magnesium, aluminum)
  • best to be taken on an empty stomach
  • doses to be taken at a consistent time, once daily
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16
Q

Thyroid supplementation adverse effects

A

Similar to hyperthyroidism:

  • cardiac effects: tachycardia, atrial fibrillation
  • tremor
  • anxiety
  • diarrhea
  • reduction in bone mineral density
17
Q

Liothyronine compared to Levothyroxine

A
  • shorter half life, more fluctuation in levels
  • increased risk of cardiovascular adverse effects
  • possible alternative to Levothyroxine if patients cannot tolerate that drug
18
Q

Combining of T3 and T4

A

Dessicarted thyroid is an older product with T3 and T4 (porcine source)
Problems: quality unreliable (variation)

19
Q

Anti-thyroid drugs

A 
Thyroid peroxidase inhibitors (thionamides)
Radioactive Iodine (I131)
20
Q

Thyroid peroxidase inhibitors examples (Thionamides)

A

Methimazole

Propylthiouracil (PTU)

21
Q

Thyroid peroxidase inhibitors mechanism

A
  • inhibit various stages in Thyroid hormone synthesis

- PTU also inhibits the peripheral conversion of T4 to T3: better for managing thyroid storm (very high TH)

22
Q

Thionamides mechanism

A
  • inhibit thyroid peroxidase: inhibition of iodinated (adding of Iodine to tyrosine)
  • inhibits coupling of MIT and DIT
23
Q

Thionamides adverse effects

A
  • Caution using in pregnancy (first trimester)
  • rash
  • hypothyroid- like symptoms
  • Serious/rare: Agranulocytosis, Hepatotoxicity
24
Q

Radioactive Iodine example

A

Iodine 131

25
Q

Iodine 131 mechanism

A
  • radioactive Iodine taken up by the thyroid gland
  • destroys the gland
  • contraindicated in pregnancy
26
Q

Adverse effects of Iodine 131

A
  • Hypothyroidism: gland is destroyed so patients will likely require supplementation
  • damage to salivary glands: results in dry mouth, tooth decay
  • altered taste sensation
  • Pain
27
Q

Other options for Antithyroid

A

Iodide

28
Q

Iodide based examples

A

Saturated solution of Potassium Iodide (SSKI)

Lugol’s solution (iodine/potassium iodide)

29
Q

Iodide based drugs mechanism

A
  • taken up by thyroid, inhibits TH synthesis/release

- Wolf-chaikoff effect

30
Q

Thyroid drug interactions

A
  • drugs that contain iodine or overuse of iodine may lead to hyper- or hypothyroid-like state
    Example: Amiodarone
31
Q

Adjunctive therapy for Hyperthyroid

A

Problem: Tachycardia
Solution: Beta-blockers

Problem: inflammation
Solution: anti-inflammatories

32
Q

Treatment options for thyroid cancer

A

Surgery

I131

PHPY 305 (14 decks)

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