Step I T3 Effect on TRH

[HalladayWeekend]

So I I understand that increased T3 levels feedback inhibit on the anterior pituitary by downregulating TRH receptors (thus decreasing TSH release). Does this mean that TRH will "reflexively" increase in this scenario (but not be as effective in stimulating TSH because of the decreased number of receptors. I haven't come across a question in UWorld on this but want to make sure I have this down in case I get an arrow question on this on the real exam!

 

[Step1Hash]

So I I understand that increased T3 levels feedback inhibit on the anterior pituitary by downregulating TRH receptors (thus decreasing TSH release). Does this mean that TRH will "reflexively" increase in this scenario (but not be as effective in stimulating TSH because of the decreased number of receptors. I haven't come across a question in UWorld on this but want to make sure I have this down in case I get an arrow question on this on the real exam!

I had though t3 feedback inhibited both the Hypothalamus as well as Pituitary and show you won't get a 'reflexive' increase in TRH.

Source: Class lecture notes.

 

[HalladayWeekend]

As per p. 295 of 2011 First Aid and p. 234 of BRS Physio, T3 is only shown feedback inhibiting on the Anterior Pituitary.

 

[Step1Hash]

As per p. 295 of 2011 First Aid and p. 234 of BRS Physio, T3 is only shown feedback inhibiting on the Anterior Pituitary.

I don't have any textbooks to quote but did find this figure in this paper. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1533213/?page=2

if you search thyroid axis on google images almost all of the pictures so negative feedback to both...some showing that the hypothalamic negative feedback is in fact less than that of the pituitary but still present.