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Old 08-10-2012
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Question Binding globulin effects on circulating hormones!

In first aid 2012 page 322 says with increase or decrease SHBG we have decrease and increase in free testosterone ==> gynecomastia or hirsutism accordingly
But Goljan says with increase or decrease TBG in pregnant or lifter we have normal free T4 ==> asymptomatic !!!
Can someone explain this?
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Old 08-10-2012
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in Pregnancy inc TBG (Thyroid Binding Glubulin) is secondary to high Estrogen that inc total serum T4; but not free serum T4 (assymptomatic) hyperthyroidism is as a result of inc total+free T4.

Dec SHBG to bind Steroid/Thyroid Hormone around in blood that increases free Testosterone in women which causes hirsutism

AS A RULE IF A HORMONE IS BOUND IT DOES NOT EXERT ITS EFFEC, ONLY FREE SERUM HORMONES WILL EXERT EFFECT.
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Old 08-10-2012
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Remember that SHBG has greater affinity for testosterone than estrogen(estrogen amplifier) so if we increase SHBG we decrease free testosterone levels and reverse is true in case of hirsuism in women ie
(Androgens/obesity/hypothyrioidsm/PCOD)-----> decreases SHBG-----> hence increase free testosterone levels

While in pregnacy estogen stimulates production of TBG so free T4 decreases but because of negative feed back T4 production increases so has to maintain NORMAL FREE T4 LEVELS(hence no clinical symptoms) BUT INCREASED TOTAL THYROXINE LEVELS.

hope that helps
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Dr.Lacune (08-16-2012), pathophysio (09-14-2016), saman49 (08-11-2012)



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