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Instructions: Read the text. Look at the diagrams. When you're finished, click "Next".
It is important that a normal and healthy amount of T3 and T4 are present in the blood and interacting with target cells.
The body has a negative feedback mechanism (loop) to ensure that concentration levels of T3 and T4 are not too high or too low... in other words, to maintain homeostasis.
1. Hypothalamus gland in the brain sends a releasing hormone to the anterior pituitary gland
2. In response, the anterior pituitary releases thyroid stimulating hormone (TSH) into the bloodstream
3. TSH travels to the thyroid gland
4. The thyroid gland releases T3 and T4 into the bloodstream
5. Increased levels of T3 and T4 have a negative feedback effect on the hypothalamus and pituitary. As a result, TSH is not secreted until the production of more thyroid hormones is needed.
Figure 7. Thyroid negative feedback loop
Study Tip: To help you learn a step-by-step process like this negative feedback loop involving the thyroid, use pencil and paper to draw and label the diagram from scratch.
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