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Questions and Answers
What enzyme is responsible for hydrolyzing thyroglobulin in the follicular cells?
Which statement is TRUE about the iodide removal from T4?
During which condition is reverse T3 predominantly produced?
What happens to MIT and DIT after they are produced in the follicular cells?
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Which component is reused in thyroid hormone synthesis after deiodination of MIT and DIT?
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What percentage of T4's iodide is removed to convert it into T3 in target tissues?
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Study Notes
Thyroid Hormone Synthesis
- Upon stimulation of the thyroid gland by TSH, colloid (containing thyroglobulin) reenters the follicular cell, where thyroglobulin is hydrolyzed by lysosomal enzymes.
- This process yields T4, T3, MIT, and DIT.
- T4 and T3 are released into the circulation, while MIT and DIT undergo deiodination by a deiodinase enzyme, resulting in tyrosine and iodide, which are reused in thyroid hormone synthesis.
Peripheral Conversion of T4
- A peripheral deiodinase enzyme (containing Selenium) in target tissues (pituitary, kidney, and liver) selectively removes iodide from the 5' position of approximately 80% of T4, converting it to T3.
- T3 is 3-4 times more active than T4, and T4 is considered a prohormone.
- In certain circumstances (e.g. starvation, chronic illness, surgery, and certain drugs), the peripheral deiodinase enzyme converts T4 to reverse T3 (rT3), a weak thyroid hormone, instead of T3.
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Description
Learn about the process of thyroid hormone synthesis, including the release of T4 and T3, and the deiodination of MIT and DIT.
