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regub 6: effects of hyper + hypothyroidism 1 (general info (TH acts slowly…
regub 6: effects of hyper + hypothyroidism 1
general info
thyroid gland = one of the largest endocrine glands (15-20 g)
almost all of T4 converts to T3 (stripped of iodine outside gland)
T3 = more active + x10 more potent than T4
TH acts slowly
response detectable after a few hours
max response not evident for days
TH not degraded rapidly
long response duration (weeks)
TH not essential for life, but essential for normal development + physical/mental wellbeing
almost every tissue directly/indirectly by TH
in general increases functional activity
calorigenic effect causes peripheral vasodilation to carry excess heat to surface for elimination
TH essential for growth
but hyperthyroidism does NOT cause excess growth
affects GH + IGF 1
-ve feedback of TH on TSH maintains stable daily levels
TSH + TRH affected by emotions
abnormalities in thyroid function = most common endocrine disorder
TH synthesis begins in 2nd trimester
critical brain growth in last 6 months foetal life + first 6 months born
hypothyroidism
causes
primary: failure of gland
autoimmunity (Hashimoto's)
secondary: TSH/TRH deficiency
iodine deficiency (>50 mg/yr)
symptoms largely caused by decreased BMR
cold intolerance
weight gain
fatigue
slow weak pulse
somnolence
slow reflexes, speech + responsiveness
diminished alertness + memory
myxoedema (total lack)
cretinism
hypothyroidism from birth
dwarfism + mental retardation
congenital = lack of gland
genetic = failure of gland to make TH
endemic = iodine deficiency
neonate may look/function normal @ first
maternal TH supply
sluggish movements a few wks after birth
must be treated in a few weeks to avoid permanent mental retardation
treatment = thyroxine/iodine supplements
diagnostic tests
elevated TSH
blood thyroxine