Endo 4: Thyroid Disorders - hypothyroid Flashcards
What happens in primary hypothyroidism ?
- you get autoimmune damage to the thyroid
- thyroxine levels decline
- TSH levels climb
What are symptoms of primary hypothyroidism?
(EVERYTHING SLOWS DOWN)
- deepening voice
- depression + tiredness
- cold intolerance
- weight gain w reduced appetite
- constipation
- bradycardia
A healthy thyroid gland secretes hormones ___ and ___
A healthy thyroid gland secretes hormones T3 and T4
What is a prohormone of T3?
T4
What enzyme converts T4 to T3 ?
deiodinase
Explain the mechanism of action of thyroid hormone.
- thyroxine enters target cell
- it is converted to T3 by deiodinase
- T3 moves to the nucleus
- and binds to the thyroid hormone receptor
- it then heterodimerises with a retinoid X receptor
- This complex then binds to the thyroid response element
- which causes a change in gene expression.
What is a common thyroid hormone replacement therapy?
what is another alternative?
- levothyroxine sodium (T4)
less common:
- liothyronine sodium (T3)
What are the different clinical uses of levothyroxine sodium?
Used for:
- primary hypothyroidism
- oral administration
- TSH level = used as guidance for thyroxine dose - Secondary hypothyroidism
- oral administration
- TSH level = CANT be used as a guide
(due to low TSH from anterior pituitary failure)
What are the different clinical use of Liothyronine?
used for:
1. Myxoedema coma
How should you respond to myxoedema coma ?
Myxoedema coma
- give IV Liothyronine (due to faster action than T4)
- then give oral thyroxine replacement
Why might you give combined thyroid hormone replacement to a patient?
- some patients don’t feel better with T4 even if their TSH is normal
- so combination given
What side effects may combined thyroid hormone replacement have? and why?
- T3 = very potent
- so difficult to get the dose right
side effects:
- thyrotoxicosis.
(palpitations, tremor, anxiety)
- often combination treatment can causes suppression of TSH
What are some adverse effects of thyroid hormone over-replacement?
(skeletal, cardiac, metabolism, increase B-adrenergic sensitivity)
Skeletal:
- increased bone turnover
- reduction in bone mineral density
Cardiac:
- Tachycardia
- risk of dysrhythmia
Metabolism:
- increased energy expenditure
- weight loss
Increase B-adrenergic sensitivity:
- tremor
- nervousness
–> ALL SYMPTOMS OF THRYOTOXICOSIS
what is a treatment method for hypothyroidism?
- give thyroxine
- -> patients will lose weight, tiredness + depression alleviated
How does measurement for dosage guidance differ between primary and secondary hypothyroidism?
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