Here we have the second in our endocrine system lab presentations covering the thyroid gland and the parathyroid glands. These images are four of the images that you have available in the photo folder in the module, and I'll briefly describe them. This image down here, first image, is the trachea and the larynx, which is that upper portion, that upper sort of solid blue portion. See the highway bone above that?
But then the thyroid gland is that globular-looking thing below it. If you flip that around, so this is the thyroid gland right there. If you flip that whole thing around so you're looking at it from the dorsal surface, you see each of these little guys here are the parathyroid glands, and that's a model version of it. And the third image, this is a rat dissection. And I've got the probe pointing down here.
right at the top of this trachea. Now it's not real visible, but there's a kind of a little shiny white thing there. That's one of the lobes of the thyroid gland. Now here's that hint I put up there.
If you see a rat and it's got a pointer way up near the top of the trachea, and we're talking about the endocrine system, it's nothing respiratory. That's the second half of the semester. So the only thing that can be there is the thyroid and parathyroid glands. And then in the fourth image, this is a microscope image.
with the thyroid gland being on the left and the parathyroid gland being on the right. This one right here has got an opening. You know, it's kind of hollowed out, but that's just a preparation. Normally, they're going to have this stuff in there, and this stuff is called colloid. So you see a follicle, which is the entire thing.
Colloid's this stuff here in the middle. These cells right here are called para... I'm sorry, follicular cells. They're not parafollicular cells.
Those are follicular cells. So these two things right here, the follicular cells and the colloid make up a follicle. And that's where you make, as you'll see, thyroid hormone. Now these other cells that are kind of wedged in between over here, these guys like this, I'm kind of drawing on it right now, those are called parafollicular cells. Parafollicular cells are the ones that make calcitonin.
Now over on the right side of image four, you see this big purple, blue looking thing. That is a parathyroid gland, and I'll always show you in a slide the parathyroid and thyroid juxtaposed so that you can identify the parathyroid. The thyroid should be very easy to identify all by itself. Okay, moving on to the text slide. So here it is talking about thyroid gland hormones, and the main ones, or I shouldn't say the main, but the ones you think of first are thyroid hormone, right?
And I've written thyroid hormones because there's a few different versions of them. You may have to know those in lecture, but in lab, just know it's thyroid hormone. And there's two main versions of that, T3 and T4.
The names are rather intractable, so I'll spare them to you. Like I said in the previous slide, the follicles make them. So that's the follicular cells and the colloid. This is a process that you have to get done and requires iodine. People that are iodine deficient can develop enlarged thyroid gland called a goiter, and that's due to the fact that the thyroid's getting bigger and bigger to try and catch more iodine, which isn't really there if you're deficient in it.
Anyway, these guys, or these hormones increase metabolic rate, heart rate, respiratory rate, basically just up your metabolic rate and all the things that go along with that. And it can also stimulate growth synergistically with growth hormone in children. If you have over or under production, it can lead to a number of different disorders.
I've already mentioned iodine deficiency. Graves'disease is an autoimmune disease, which causes an enlarged thyroid. So you can get hyperthyroidism due to this autoimmune disorder.
So lots of things are kind of what's one is the cause and the other is the effect. And just be aware that Graves'disease is a thyroid. affecting disease. It causes real bulgy eyes and some metabolic problems. Hypo and hyperthyroidism in general just mean low thyroid function or high thyroid function.
And as I say, they can result from other things and cause their own disorders as well. Uh, one other hormone called calcitonin. Now this is produced by the parafollicular cells. So if you think thyroid hormone, you're thinking the follicles and the colloid.
And if you think calcitonin, think the parafollicular cells, the spaces in between. This hormone decreases blood calcium levels. Osteoclasts, if you remember from ANP1, are the cells that break down bone. So If you're decreasing blood calcium levels, it means that the calcium's got to go somewhere.
Generally, it's going into the bones. If you stop the cells that break down bone, you're going to have a net increase in bone density that follows from that decrease in blood calcium. An additional effect of calcitonin is that it slightly inhibits calcium reabsorption by the kidneys, so that means that you're going to urinate more calcium.
But these guys work together. So calcitonin and... parathyroid hormone, which will be discussed next, are antagonists, but at the same time, they work together to remodel your bones. Parathyroid hormone produced by the parathyroid glands does the opposite. That's why I said it's an antagonist.
So it increases blood calcium levels, stimulates osteoclast activity. That's how you get that done. If you stimulate the cells that break down bone, the calcium gets liberated from the bone and has to go somewhere, your blood. And another effect of parathyroid hormone is that it helps you synthesize vitamin D.
So just remember that parathyroid hormone and calcitonin are antagonists, but they also then they don't hate each other. That's not what it means by antagonist. They just do opposite things. But those two opposite things work to keep your bones healthy.
and keep the correct amount of blood calcium.