tsh - strongman

[ArchivalUser]

a lady takes t4 to lose weigt, and it is found that her TSH is deeply suppressed. which hormone suppresses TSH, free t3 or free t4?

[ArchivalUser]

Free T3

[ArchivalUser]

free t4 according to Kaplan
free t3 according to others

My answer is: free t4 as I go with Kaplan guy!! I don care what others say..

[ArchivalUser]

If u see the kaplan notes thoroughly, serum t4 goes to hypothalamus nd there converted to t3 to cause feedback .
so while its t3 doing the final thing,t4 level is the one thats determining it,kind of twisty

[ArchivalUser]

I agree with u to certain extent madhuri but not thoroughly... Can u explain this!!

Ok.. let us believe that t3 controls tsh secretion..

then in relative Iodine deficiency.. where t3 synthesis is higher than t4.. why u see euthyroid goiter???

Its twisty but I will apreciate if u can explain this same..

[ArchivalUser]

yes, according to kaplan, it is free t4, uw says free t3. i think it should be free free t4. t4 conversion to t3 occurs at the tissue level, so the free t3 is very low in this pt.

[ArchivalUser]

Yes strong man.. cellular level (INSIDE THE CELL) the t4 is converted to t3... and its the actual final regulator.. but plasma free t4 is the one that enters the hypothalamic and pituitary cells readily than t3...

So t4 is the main regulator to enter the cells and t3 at intracytoplasmic receptor level. Hop[e this clarifies.

[ArchivalUser]

sorry for being late,I was checking other messages

relative iodine def. has no rise in t4,if it were increased it would go to hypothalamus nd convert into t3 in thyrotrophs

t4 to t3 conversion occurs in thyrotrophs aswell

[ArchivalUser]

yes thats it

[ArchivalUser]

So the bottom line is T4 is the main regulator and its plasma conc can change TSH conc.
T3 acts at intracytoplasmic levels.. final regulator.. but its plasma conc hardly can change TSH.