case 9 - thyroid gland and thyroid hormone Flashcards
where is TRH released from
the hypothalamus and acts on the anterior pituitary
what does the anterior pituitary then release
TSH from the anterior pituitary
what does this TSH do
it activates the thyroid - T3 and T4 secretion
what is thyroid hormone formed from
sequential iodination of tyrosine
what is thyroid hormone stored as in the thyroid gland
colloid
what is T4 produced by
entirely by the thyroid
what is T3 produced by
partially by the thyroid, however peripheral T4 mono-deiodination in the liver and kidney make it metabolically active??
what is the half life of T3 and T4
half life of T3 is 1-3 days and half life of T4 is 5-7 days
T3 has to be given three times daily, T4 once daily
what does TR do
acts in the nucleus on gene expression, therefore thyroid hormone effects are slow
what does TR do
acts in the nucleus on gene expression, therefore thyroid hormone effects are slow
what is the HPT axis regulated according to
the principles of negative feedback; for primary thyroid disorders, TSH indicates thyroid status - a biomarker
what is a goitre
an enlarged thyroid gland
what is the active form of thyroid hormone
T3
where does T4 get converted
in the peripheral tossues
what does T3 do
regulates gene expression - for it to have effect it has to get into the cell and turn genes on - it is a slow process
what is the aetiology of primary hypothyroidism
autoimmune thyroiditis (Hashimoto disease)
4.1/1000 females; o.6/1000 males per year over 20 years, increasing
5% of over 60s
Classic Hashimoto (goitrous)
Atrophic (non-goitrous)
In reality, a mix of antibody mediated/ T cell mediated
TPO, TSHR, Tg auto-antibodies - most important one is TSH
what drugs can cause hypothyroidism
drugs (amiodarone, iodides, lithium) - these can cause hypothyroidism
what is the aiteology of secondary hypothyroidsm
pituitary adenoma, congenital deficiency, irradiation
Sarcoid, infection
what are the symptoms and signs of hypothyroidism
insidious
Weight gain
Cold intolerance, particularly at extremities
Fatigue, leathery
Depression
Mentally slowed, dull, expressionless
Coarse skin, puffy, (possible carpal tunnel syndrome) - aminoglycans
Dry, brittle, thinning hair
Hoarse voice
Constipation, faecal loading
Menstrual disturbance
Muscle stiffness, cramps, slow-relaxing reflexes
Generalised weakness and paraethesias
Cerebellar ataxia
Bradycardia
Macroglossia
family history
History of other autoimmune disorders