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Flashcards in Thyroid Hormone Physiology Deck (20)
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describe how thyroid hormones are transported in the body

vast majority bound to serum proteins, very small amount is free


what serum proteins do thyroid hormones bind to

thyroxine binding globulin(TBG) 70%
thyroxine binding pre-albumin(TBPA) 20%
albumin 5%


what form of T3 and T4 is available to the tissues

only the free T3 and T4, not the vast majority of hormones bound to serum proteins


describe the readiness of binding by T3 to serum proteins, and what this results in

bound 10-20 times less avidly to TBG, and not significantly by TTR, means T3 has more rapid onset and offset of actions


how does the metabolic state correlate to thyroid hormone levels

correlates more closely with free than the total conc. in plasma


what is the effect on T4 when TBG is increased or decreased in certain states

when TBG increased = total T4 increased but free T4 unchanged
when TBG decreased = total T4 decreased but free T4 unchanged


what are some states that result in decreased and increased TBG

increased = pregnancy, Hep A, newborn
decreased = Cushings, chronic liver disease


what affects do thyroid hormones have on all cells, especially neurons

increase metabolic rate, and increase glucose uptake


what effect do thyroid hormones have in the liver

increased glycogenolysis and gluconeogenesis, decreased glycogenesis


what effect do thyroid hormones have in adipose tissue

increased lipolysis and decreased lipogenesis


what effect do thyroid hormones have on the heart and lungs

heart = increase HR and increase contractile strength
lungs = increased breathing rate


in what ways do thyroid hormones increase the basal metabolic rate

increase number + size of mitochondria, increase O2 use and rates of ATP hydrolysis, increase synthesis of respiratory chain enzymes


what effect to thyroid hormones have on temp. regulation

~30% temp. regulation is due to thyroid hormone thermogenesis


what effects do thyroid hormones have on carbohydrate metabolism

increase blood glucose and increase insulin-dependant uptake of glucose into cells


what effects do thyroid hormones have on lipid metabolism and protein metabolism

lipid = mobilise fats from adipose tissues and increase fatty acid oxidation in tissues
protein = increase protein synthesis


what role do thyroid hormones have in growth

growth hormone releasing hormone(GHRH) production + secretion, glucocorticoid-induced GHRH release and GH activity all requires thyroid hormones
(permissive actions)


what role do thyroid hormones have in development of foetal and neonatal brains

myelinogenesis and axonal growth requires thyroid hormones


what permissive sympathomimetic action do thyroid hormones have

increase response to adrenaline + sympathetic NS neurotransmitter, noradrenaline, by increasing number of receptors


what is responsible for the degradation of thyroid hormones

the de-iodinases, 3 types D1, D2 and D3
(D3 main one)


where are D1, D2 and D3 found

D1 = mostly liver and kidney
D2 = thyroid, pituitary, heart, some peripheral tissues
D3 = foetal tissue, placenta, brain(not pituitary)