Very thorough explanation. Probably more than most nursing students will need when trying to understand the HPT axis in the evaluation of TSH, T3, T4 lab results.
That’s a good question. I would begin by looking in the endocrinology section of any physiology book. Then I would work my way towards more advanced endocrine textbooks to fully understand what the thyroid hormone does.
kaplan physiology usmle step 1 aid says t4 is major negative feedback to tsh other books say it is t3..you also say t3 should i stick with t3 or t4 kindly reply
Hi Rohit, Excellent observation. Yes, Kaplan does state that "circulating T4 is responsible for most of the negative feedback". However, that is an oversimplification of the mechanism. The Medical Physiology textbook (Boron and Boulpaep) states that circulating free T4 and T3 inhibit both the synthesis of TRH in the hypothalamic neurons and the release of TSH by the thyrotrophs in the anterior pituitary. Thus the plasma [TSH] is very sensitive to alterations in free T4 and T3. However, at the level of the thyrotroph, the sensor in this feedback system monitors the concentration of T3 inside the thryotroph by decreasing the number of TRH receptors, i.e., indirect feedback. In the direct feedback system, intracellular T3 inhibits synthesis of TSH. With that in mind, I recommend the following approach: 1. If the responses to the question do not specify mechanisms of negative feedback, then choose "free T4", or "serum T4". 2. If the question/responses suggest a mechanism or mention "indirect feedback" or "direct feedback", then choose "T3" or "intracellular T3". Hope that helps. Cheers, Lance
Very thorough explanation. Probably more than most nursing students will need when trying to understand the HPT axis in the evaluation of TSH, T3, T4 lab results.
Thank you very much for displaying the interesting
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Help, I’m confused. What do I need to learn first in order to fully understand the concept of what this video is explaining?
That’s a good question. I would begin by looking in the endocrinology section of any physiology book. Then I would work my way towards more advanced endocrine textbooks to fully understand what the thyroid hormone does.
does the T3-THR complex bind to both Gata-2 and Pit-1 at the same time to inhibit tsh synthesis? or is it either one?
kaplan physiology usmle step 1 aid says t4 is major negative feedback to tsh
other books say it is t3..you also say t3
should i stick with t3 or t4
kindly reply
Hi Rohit,
Excellent observation. Yes, Kaplan does state that "circulating T4 is responsible for most of the negative feedback". However, that is an oversimplification of the mechanism. The Medical Physiology textbook (Boron and Boulpaep) states that circulating free T4 and T3 inhibit both the synthesis of TRH in the hypothalamic neurons and the release of TSH by the thyrotrophs in the anterior pituitary. Thus the plasma [TSH] is very sensitive to alterations in free T4 and T3. However, at the level of the thyrotroph, the sensor in this feedback system monitors the concentration of T3 inside the thryotroph by decreasing the number of TRH receptors, i.e., indirect feedback. In the direct feedback system, intracellular T3 inhibits synthesis of TSH. With that in mind, I recommend the following approach:
1. If the responses to the question do not specify mechanisms of negative feedback, then choose "free T4", or "serum T4".
2. If the question/responses suggest a mechanism or mention "indirect feedback" or "direct feedback", then choose "T3" or "intracellular T3".
Hope that helps.
Cheers,
Lance
تسش=4.8 ت4=12