 Trust it. Hey everybody, Dr. O here. We're going to talk about the thyroid gland and the hormones that it produces here today. So first look structurally at the thyroid gland, you can see it there at the top, it's a butterfly shaped organ, it's sitting just below the larynx, your voice box, it sits right in front of your trachea or what we call the windpipe, it has the two lobes one on each side with that little isthmus, that narrow arrow area in between it. So that's the gland itself. So what does it do? The thyroid gland is primarily like the functional unit of the thyroid gland would be called the follicle. So it's full of these follicles which you can see at the bottom and the follicles are full of this sticky substance called colloid which has thyroglobulin in it and iodine and your body uses those to make thyroid hormones. So this soup, this colloid inside the follicles is where thyroid hormone is going to be produced. Thyroglobulin needs the amino acid tyrosine, we talked about that earlier in the major classes of the hormones. Another thing you see on here is you'll notice it says paraphilicular cells, I usually call those C cells, those are going to be the cells that produce a separate hormone called calcitonin. So that is your thyroid gland there, we'll cover the parathyroid glands in a separate video. So here we see thyroid hormone production and its function. So you take this thyroglobulin which has that amino acid tyrosine and you add iodines to it to make the thyroid hormones. There are two primary thyroid hormones, T4 and T3. Now there are technically T2, T1, even T0 but T4 and T3 are all we care about. T4 by far more common, so the huge majority of thyroid hormone is T4, but T3 is much more metabolically active. So I like to think of T4 as almost like a storage form of thyroid hormone. So T4 is called that, its actual name is thyroxine, but it's called that because it has four iodines, T3 or triiodothyronine has three. Tyrosines have enzymes that can lop that fourth iodine off making your thyroid hormone more metabolically active. The huge majority of your thyroid hormone is actually going to be bound. Remember earlier we talked about bound versus free hormones. Free hormones are active for less than an hour until they get broken down. Bound hormones are basically being carried through your body. So about 99% of your thyroid hormone at any moment is going to be bound to different proteins but thyroxine binding globulin would be the most important one. And then when your body needs it, it will take it off of that transport protein, activate it and then hopefully it will become that more metabolically active T3. So as far as what it does, so remember thyroid hormones are kind of unique because even though they're made of amino acids, their lipid soluble has to do with their structure. But they enter the cell and if they attach to receptors on the mitochondria, which you can see here on the right hand side, they will increase oxygen utilization and fuel utilization, you'll burn more fuel, you'll generate more ATP. They also can dock on receptors inside the nucleus on your DNA and they can affect the expression of genes involved in the oxidation of glucose. So as you can see, the primary functions of your thyroid hormones would be to control your metabolism too. If you have a lot of thyroid hormone, it would increase your metabolism and then vice versa. But thyroid hormone has other impacts too. That appears to be very important to the function of your reproductive hormones and also to the development of your nervous system. It's one of the key growth hormones. We think of growth hormone and your sex hormones, but without thyroid hormone, the rest of these growth related hormones don't actually work and its role in the function of the nervous system is very well known and very, very important. So we'll talk about that more in just a moment. Here I already showed you this image in an earlier video as far as the feedback system used, but we'll just go through it real quickly. If we need more thyroid hormone, if we need more T3 and T4, then thyroid tropon releasing hormone from the hypothalamus will send a signal to the pituitary gland to release thyroid stimulating hormone, which will send a signal to the thyroid gland to produce and release thyroid hormones. So we've already walked through that feedback loop earlier. Okay. Here we see a goiter. So a goiter would be if someone had hypothyroidism, you'd see an enlargement of the thyroid gland. So the thyroid gland is trying to make thyroid hormone, but in most cases, at least in the developing world, it's because of an iodine deficiency. So the thyroid gland, the follicles are producing more of this colloid, producing more of this thyroid globulin, but you don't have the iodine to actually make thyroid hormones. So the thyroid gland just starts to swell and get bigger and bigger. That is the most common cause of hypothyroidism worldwide would be iodine deficiency. But in parts of the world, well, before we talk about the impact here, it's especially important to make sure you get enough iodine in your diet when you're pregnant, because neonatal hypothyroidism or cretinism will lead to short stature and mental developmental issues. So it's the leading cause of mental developmental issues in the world. Some researchers believe that if we could eliminate iodine deficiency and all people, especially all women that become pregnant had enough iodine in their diet that the average human's IQ might grow four or five points, which would be a huge, huge deal. So worldwide, the most common cause of thyroid disorders is iodine deficiency. But in parts of the world where there's plenty of iodine, like here in the United States, we iodize our salt, which then your doctor tells you not to use it, right? The most common cause of hypothyroidism in the developed world is inflammatory condition, the most common one being an autoimmune condition called Hashimoto's thyroiditis. So an inflammatory condition would cause the swelling of the thyroid gland in that instant. What else about that? That's your thyroid hormones. That's how they function. I did mention earlier that the paraphilicular cells or C cells of the thyroid gland produce a different hormone. So when you think thyroid gland, think thyroid hormone. But there is also the hormone calcitonin. Calcitonin's job is to decrease blood calcium levels. So if there is a lot of calcium in your blood, then calcitonin will find a way to bring blood calcium levels down. This hormone appears to be especially important when we're young, which is good because we take this calcium and we hopefully put it into bones. So what calcitonin does is it increases the activity of osteoblasts. Those would be the cells that build bone, take calcium from your body fluids and build bone with it. It would inhibit the osteoclasts that break down bone, which is why when you're younger, you're building up more bone than you're breaking down and you reach peak bone density somewhere between 14, 18, maybe as high as the early 20s, but for most people somewhere in there, because you have a lot of this calcitonin. And then the other things that calcitonin will do is it will decrease the absorption of calcium in the intestines and then also it'll increase the amount of calcium we lose in our urine. But the big ones are it turns on the cells that build bones, turns off the cells that break it down. So that's calcitonin. Thyroid hormone is more important. So all right, those are your thyroid hormones. T3, T4 and calcitonin. I hope this helps. Have a wonderful day. Be blessed.