Re: Thyroid hormone conversion... T4 to T3, how does it work?

[Guest guest]

Don't feel like a dunce.. it took a while for me to 'get it' too...

T4 is the thyroid storage hormone. The thyroid gland makes mostly T4.

T4 contains, among other things, 4 iodine molecules.

Imagine a puzzle piece... a T4 molecule is like a puzzle piece with four of those little 'peg's coming off it. It uses those 'pegs' to attach to hormone receptors. The receptors have the little 'cut outs' that the 'pegs' fit into.

If the hormone is the right shape for the receptor and fits, then it attaches itself.

So T4 is stored.

The body needs the other thyroid hormones, the active thyroid hormones, T3, T2, T1 to function. Those have to be made... converted from other hormones.

A T4 hormone is used to start with. Through a chemical process, called conversion, energy is used to attach a selenium molecule to one of the iodine molecules on the T4 molecule... and YANKS it off. Now the T4 is a T3. It's shape is different, it is able to attach to a T3 receptor, and the body is able to use it for all the stuff that it needs the T3 for.

To make a T2 molecule.... one of the T3s has an iodine molecule removed the same way, by attaching a selenium molecule to one of the iodines and YANKING it off.

And for a T1, a T2 gets an iodine molecule removed.

If the wrong 'peg' gets yanked off it becomes a Reverse hormone. They have functions too... but more of a balance thing. For example Reverse T3 is manufactured to reduce metabolic rate.

Making a bit more sense?

For conversion to happen we need energy (so regular meals, no skipping meals), we need selenium (if we don't get enough in the foods we eat we use a supplement), and our body has to be capable of converting.

Some of us have trouble converting, though it's not known why.

For some its the form of hormone they take, some do better with natural, some with synthetic.

For some it's nutrition, they have to get rid of more of the goitrogens, like soy and HFCS and such, or add selenium.

For some it's not eating often enough.. once or twice or even three times a day is not often enough and skipping breakfast is WAY bad for conversion.

While I'm at it.... TSH is not a thyroid hormone. It's a pituitary hormone. As the body determines an adjustment in thyroid hormone production is needed it either increases or decreases the amount of TSH released from the pituitary. The TSH, Thyroid Stimulating Hormone, can be likened to a loud speaker.

The higher the TSH level the louder the volume is turned up.... yelling at the thyroid gland to get it's production up, the body needs more thyroid hormones... when the TSH is low then the volume has been turned down, not as much production is needed.

Most happy healthy normal folks have a TSH of 1.25... so that would be about where the loud speaker is just kinda humming along saying all is well, there is a balance happening and no one needs to panic.

For us, those on hormone replacement. We need to look at TSH a bit different. It doesn't tell us a heck of a lot about anything.

If it's over 2 we know our replacement levels (how much hormone we are taking each day) is too low.

If it's under 1, we know that there is little stimulation to the thyroid gland, exactly where we want to be if dealing with an autoimmune thyroid thing (like Hashi's or Grave's)

If it's approaching zero we know that there is VERY little stimulation for to the thyroid gland.. which is even better when dealing with the autoimmune stuff... and it's pretty much mandatory for folks with zero gland function.

The more accurate picture on how we are doing, thyroid hormone level wise, is to test the actual hormone levels. Free T4 and Free T3.

Free means that they are free, unbound, unattached, ready for the body to use, and floating around in the blood, not yet attached to a receptor.

If the level of the Frees are too low, regardless of the TSH, we will feel hypo.

If the levels are disproportionate to each other (high Free T4 and low Free T3) we will feel hypo.

I'll stop with that.... and let you ask the next questions.... it takes time to get it all straight......

Some of this stuff is up on the website if you want to review....

www.thyrophoenix.com/thyroid_101.htm

I touch on some stuff about the tests and meds there too...

Topper ()aka ThyroGeek

On Sat, 20 Jan 2007 21:57:17 -0800 Ken & Jackie Reimer writes:

I feel like such a dunce. I still don't understand the whole T-3 and T-4 thing.

I know one helps the other convert, but when i see the e-mails that talk about them, I am like a deer in headlights.

Does anyone have a "child-like" analogy to explain this to me?

Thanks, Jackie