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agate_ t1_j921et4 wrote

Reply to comment by Bbrhuft in Why does the thyroid use iodine ? by geistererscheinung

This is a neat answer, but I hope someone will tackle what I think is the most interesting part of OP’s question: why is iodine biochemistry apparently localized in the thyroid? It’s not like we have specific organs for zinc or manganese chemistry. (Or do we?)

What animals have a thyroid? Is iodine chemistry localized in a different organ in the ones that don’t?

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isaacwoods_ t1_j925jbo wrote

It’s precisely because elemental iodine is very reactive. The thyroid has follicles, where iodine is pumped into a gel in ion form, and then enzymatically converted into elemental iodine, where it then attacks thyroglobulin to create thyroid hormones. The final hormones are the only molecules allowed out of the follicular lumen back into the blood.

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geistererscheinung OP t1_j94ootq wrote

Elemental iodine? In my thyroid?? Wow, that's really cool. Wikipedia said that the iodation of tyrosine by elemental iodine is a really streamlined process, indicating how T3 and T4 evolved.... Thank you for your answer!

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CrateDane t1_j9267og wrote

> > > > > What animals have a thyroid?

Vertebrates. Invertebrate chordates have an organ called the endostyle, which has some functional similarity and is very likely the evolutionary predecessor to the thyroid gland.

> Is iodine chemistry localized in a different organ in the ones that don’t?

Well... many aquatic invertebrates may rely mainly on exogenous thyroid hormones, so they don't need an organ for it. Other invertebrates may have their own endogenous production of thyroid hormones, but without a dedicated organ. Yet other invertebrates, particularly outside the bilaterians, may be less reliant on thyroid hormones in the first place, since they seem to lack an ortholog of the thyroid hormone receptor.

Here is an interesting review article about thyroid hormone signaling in invertebrates.

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geistererscheinung OP t1_j94owd9 wrote

Thank you for your answer. I'll try to read that article soon. Thyroids are turning out to be really interesting biochemically!

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thewizardofosmium t1_j92sn0v wrote

It's really no different from other hormones: they are only synthesized in one organ and then released into the body. Sex hormones are mainly (not exclusively) synthesized in the gonads, etc.

It is fascinating that the body regulates thyroid hormones the same way a chemical plant would regulate a key chemical today. The pituitary gland monitors the level of thyroxine in the blood and emits thyroid stimulating hormone in greater or lesser amounts if the thyroxine level is too low or too high. The thyroid, physically located separate from the pituitary, then produces thyroxine depending on the TSH level it senses. If the sensing function and the synthesis function were physically located at the same place, the body couldn't control what was happening.

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geistererscheinung OP t1_j94p4o2 wrote

Thank you for your answer. Kinda cool how isolated the thyroid is...yet how tightly controlled the process must be.

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geistererscheinung OP t1_j933iyi wrote

Thank you for emphasizing that. Localization was my original question, and I added the others for support.

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DrRob t1_j93ac79 wrote

Just about all hormones are made and stored in their own glands and released carefully in response to circulating chemical signals. One really unpleasant symptom cluster from cancers of hormone producing glands is indiscriminate outpouring of hormones by the now unregulated cancerous cells which are still well organized enough to produce hormones unchecked. This can happen with the thyroid, adrenals, pituitary, etc.

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Saxamaphooone t1_j93927e wrote

The majority is stored in the thyroid, but it’s also stored in the breasts, prostate, rectum, and many other places as well.

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