Hypothalamic–Pituitary–Thyroid Axis

by Thad Wilson, PhD

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    Thyroid hormones. Tyrosine or T4. And triiodothyronine which is T3. When we want to think about the hypothalamic pituitary thyroid axis we need to start in hypothalamus. In the hypothalamus we have two structures that we need to take into account. The paraventicular nucleus here and arcuate nucleus which is seen below. These are the places in which we are going to be able to secrete the substances the thyrotrope. So paraventicular nucleus secretes somatostatin and arcuate nucleus secretes thyroid releasing hormone. These are going to then be placed within the circulation of the anterior pituitary. And then the thyrotropes are what are going to respond to either somatostatin or TRH. So if we start off with the hypothalamus, we have TRH. That is going to be released to stimulate pituitary thyrotropes. But remember you have somatostatin which acts as an inhibitor to those very same thyrotropes. So if there is enough TRH around and you're able to allow those thyrotropes to release their hormone, which is thyroid stimulating hormone, that will then engage the thyroid gland. The thyroid gland will then produce T3 and T4. There is negative feedback with T3 and T4. The first portion of the negative feedback, is that it inhibits both the anterior pituitary thyrotropes to release thyroid stimulating hormone. And it also inhibits the stimulatory nuclei. And what this means is that even though thyroid releasing hormone normally is released to stimulate thyrotropes, you can't inhibit that nuclei so it doesn't release thyroid releasing hormone. Now in terms of the feedback control, you also have one more arm and that arm positively stimulates the hypothalamic nuclei that inhibits the anterior pituitary thyrotropes. So what you do is you stimulate the inhibitor or somatostatin to be released. This acts as a nice negative loop on...

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    The lecture Hypothalamic–Pituitary–Thyroid Axis by Thad Wilson, PhD is from the course Endocrine Physiology.

    Author of lecture Hypothalamic–Pituitary–Thyroid Axis

     Thad Wilson, PhD

    Thad Wilson, PhD

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