Endocrine question

[Wassupboy]

If serum auto antibodies bind to TSH receptors, would the person have high levels of thyroid because of the binding or low levels because the auto antibodies prevent binding to receptor by TSH?

Thanks

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[MedPR]

If serum auto antibodies bind to TSH receptors, would the person have high levels of thyroid because of the binding or low levels because the auto antibodies prevent binding to receptor by TSH?

Thanks

High levels of TSH and low levels of T3/T4. The thyroid would think that there's not enough TSH (since TSH isn't binding) thereby increasing TSH production by the hypothalamus. Without TSH binding, there is no negative feedback to stop or slow the production of TSH so the hypothalamus woudl keep producing it.

 

[Wassupboy]

Thanks for the reply. My friend and I were debating about this. He pointed out that the serum auto antibodies can simulate the effects of the actual TSH? Thoughts?

 

[MedPR]

Thanks for the reply. My friend and I were debating about this. He pointed out that the serum auto antibodies can simulate the effects of the actual TSH? Thoughts?

I've never heard of an antibody acting as an agonist. If it did act as an agonist though, there would be low TSH and high T3/T4. T3/T4 levels are regulated by a negative feedback on the hypothalamus (TSH). In other words, high levels of T3/T4 tell the hypothalamus to stop secreting TSH, which results in the decrease of T3/T4.

 

[loveoforganic]

Antibodies can either stimulate or block a receptor. Without it stating specifically what it does in the question stem, I would make the assumption that it blocks the receptor

 

[Hexon]

so we have an excess of TSH and low levels of T3 and T4; how would this manifest in terms of symptoms and signs?

 

[loveoforganic]

Beyond the scope of the MCAT. My assumption would be the elevated TSH doesn't lead to much, but the elevated TRH would lead to elevated prolactin and the associated symptoms of that http://en.wikipedia.org/wiki/Hyperprolactinaemia#Symptoms

 

[Wassupboy]

Antibodies can either stimulate or block a receptor. Without it stating specifically what it does in the question stem, I would make the assumption that it blocks the receptor

Alright thanks!

 

[kob3z]

ummm... you would have low TSH and high t3 t4... these ppl arent very smart. look up graves disease. symptoms would include exophthalmos, high metabolism, etc....

The autoantibodies are stimulating release of T3/T4 and these in turn have negative feedback effects on the release of TSH

 

[loveoforganic]

You're a peach. Graves' is an example of stimulation by antibody. You're not expected to know Graves' for the MCAT.

 

[MedPR]

ummm... you would have low TSH and high t3 t4... these ppl arent very smart. look up graves disease. symptoms would include exophthalmos, high metabolism, etc....

The autoantibodies are stimulating release of T3/T4 and these in turn have negative feedback effects on the release of TSH

This is the MCAT, not USMLE/COMLEX.