Thyroid hormone synthesis

[helvella]

I found this interesting and informative image the other day.

You can view the full image by following the link - but, depending on whether you are using a phone, a tablet, a computer, you might get different options and sizes of image, etc.

commons.wikimedia.org/wiki/...

Synthesis of the thyroid hormones, as seen on an individual thyroid follicular cell:[26][page needed] - Thyroglobulin is synthesized in the rough endoplasmic reticulum and follows the secretory pathway to enter the colloid in the lumen of the thyroid follicle by exocytosis. - Meanwhile, a sodium-iodide (Na/I) symporter pumps iodide (I−) actively into the cell, which previously has crossed the endothelium by largely unknown mechanisms. - This iodide enters the follicular lumen from the cytoplasm by the transporter pendrin, in a purportedly passive manner. - In the colloid, iodide (I−) is oxidized to iodine (I0) by an enzyme called thyroid peroxidase. - Iodine (I0) is very reactive and iodinates the thyroglobulin at tyrosyl residues in its protein chain (in total containing approximately 120 tyrosyl residues). - In conjugation, adjacent tyrosyl residues are paired together. - Thyroglobulin re-enters the follicular cell by endocytosis. - Proteolysis by various proteases liberates thyroxine and triiodothyronine molecules - Efflux of thyroxine and triiodothyronine from follicular cells, which appears to be largely through monocarboxylate transporter (MCT) 8 and 10, and entry into the blood.

I'd add to that, the area labelled Iodination shows three molecules of diiodotyrosine (DIT) and one of monoiodotyrosine (MIT). Count the purple dots which represent iodine atoms. These are the iodinated tyrosil molecules referred to earlier.

The area labelled Conjugation shows two molecules of DIT being linked to form thyroxine; and one of MIT and one of DIT forming triiodothyronine.

Author: Mikael Häggström.

Häggström, Mikael (2014). "Medical gallery of Mikael Häggström 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.008. ISSN 2002-4436. Public Domain.

The image is linked from this Wiki page - and it might help to view the two together:

en.wikipedia.org/wiki/Thyro...

Note: Individual follicles (what is represented by the inset at top left of the image) are of the order of 100 to 200 micrometres diameter. More detailed information, including how follicle sizes change with age, here:

rfppl.co.in/subscription/up...

[SarahJane1471]

😳😬I have no idea what this is about 😂💐

[helvella Administrator in reply to SarahJane1471]

It is an attempt to show how iodine is taken into the thyroid and thyroid hormone is formed, then released.

The thyroid gland consists of numerous follicles. That is what the inset (top left) picture tries to show. A wall of thyroid cells containing thyroglobulin. Like very small balloons.

[radd in reply to helvella]

helvella,

Errr, can we not just say ....... aided with TPO enzyme & selenium, etc, tyrosine has one or two iodines added to it to create iodination, and then 1,2 iodine atoms make MIT (mono-iodotyrosine) & DIT (di-iodotyrosine). joining up to become thyronine compounds 😬.

[helvella Administrator in reply to radd]

I am well aware that we all find different approaches work for us as individuals.

I found the diagrammatic approach I posted worked for me.

Now anyone who comes along can choose whichever approach works for them!

[radd in reply to helvella]

helvella,

I'm kidding you! 🤣

I saw this diagram in a previous reply you gave in the last few days and having seen it before it reminded me how informative it is (if available on the screen one is using), and also how I used to (for some obscure reason) always mix up the complexities of production and conversion of thyroid hormone. The diagram is brilliant! 😊

[TSH110 in reply to radd]

My head is spinning 🤣🤣🤣

[TSH110]

Very lovely diagram! Well done to the illustrator.

Thanks for posting it all helps in deepening understanding of what is glibly trotted out by some as simple, when it is is anything but - at least to my feeble mind.