intercellular communication. In other words, how does one cell communicate with other cells in the body? One way that they do this is through hormones. Now you probably know some about hormones already. For example, you know that adrenaline is going to have several effects on the body, such as increasing your heart rate and breathing rate and alertness, and you've also probably experienced the effects of testosterone or estrogen whenever you hit puberty.
But most people don't understand on a fundamental level what a hormone is and what it does. Hormones are chemical messengers. In other words, they're a substance that one cell will release in order to communicate with another cell. And that's really all that they are.
As we look at some examples, there's two things to keep in mind. One, what is the secreting cell, the cell that's releasing the hormone? And two, what is the target cell, the cell that the hormone is communicating with?
For hormonal communication to occur, we have to have both a secreting cell and a target cell. The first example we're going to look at is called... autocrine signaling.
So I'm going to draw a cell, and on my cell there's several things to point out. First, those little triangles represent the hormones that this cell contains. The circle around those is a vesicle, the little holding chamber with the membrane for those hormones.
Also in the cell are some receptor molecules on the surface of the cell or the cell membrane. In autocrine signaling, this cell is going to release some of those hormones, and they're going to bind with receptors. on the secreting cell itself.
This is an interesting example because the secreting cell in this case is also the cell being targeted. That's why it's called autocrine. Autocrine literally means self-secreting. Auto means self, secreting is that suffix crine.
It's kind of like talking to yourself. The second example we'll look at involves one cell communicating with a cell that's adjacent. So here we've got two cells.
One cell is going to contain some hormones. I drew those as little circles in the vesicle here. The other cell is going to have receptors for that particular hormone.
So the first cell will secrete those circular hormones, and they will bind with receptors on this cell. This is the secreting cell. This would be the target cell.
And this is what we call paracrine signaling. Paracrine hormones, para means next to, and crin, again, means secreting. So this literally means to secrete to a cell.
that's next to it. One common example of this, if you've studied the nervous system, this will look familiar to you, is the communication between two neurons, what we call a chemical synapse. In a synapse, we'll have the presynaptic neuron, which will secrete a hormone, which we would call a neurotransmitter, and it's going to bind with little receptors, and that's going to cause these channels to open up, and some ion will rush into that postsynaptic cell.
So that's just an example of paracrine signaling. that we see in the nervous system. Our third type of signaling, the main one that we're gonna look at in this video is called endocrine signaling. Endo means inside and crin again means to secrete. When it says inside in the word endocrine, it's referring to inside the blood vessel.
All of your endocrine hormones will travel throughout the body through blood vessels. So let's draw what this looks like. Here I've got three cells and I'm gonna make these my secreting cells.
I've also got a... blood vessel here that those hormones will travel through. And finally over here, I've got some potential target cells, and we'll talk about that in a minute.
This blood vessel is called a capillary. A capillary is just a really small blood vessel where things can move in and out of it, such as oxygen or nutrients, or in this case, hormones. So here I'll label those secreting cells.
Secreting cells are always part of what's called a gland. A gland is just any organ in the body that releases some substance either into the bloodstream or to the outside of the body. And so in the endocrine system, all of the organs that release hormones are called glands. So we've got a gland of some sort here, and inside of it, I'm going to draw some vesicles, which contain hormones. I drew these particular hormones as purple and square, even though they're not really purple or square.
It's just a good way to identify them on the diagram. And then on the other side, I'm going to draw some potential target cells that contain, like we said before, receptors. For hormonal communication to work, we have to have a secreting cell, and we have to have a target cell.
with appropriate receptors. So we'll see if any of these potential target cells will work. So, exocytosis will occur, and some of those hormones will be released to the outside of the cell.
And the capillary is gonna be porous, meaning that it's got spaces in between the different cells that make the lining of the capillary. And so these hormones will be able to travel through those little spaces. Let's watch those hormones travel through the capillary, and you can see that happening right now. They're gonna go downstream of the capillary in the direction that blood is flowing.
and eventually they're going to reach some other cell that they could potentially interact with. In this case, you can see here that I drew the receptors on this potential target cell a different color and a different receptor shape. So these receptors are not specific for this particular hormone. So nothing's going to happen.
In this case, we have a wrong receptor. and so that hormone cannot bind to it so there's no communication going on there and we would say that this is not a target cell for this particular hormone it probably is a target cell for some other hormone in the body but not this particular one that we're looking at so in the meantime these hormones are going to continue traveling through the bloodstream and see if they come up against uh a receptor that will work for them so we come to this next one it looks like oh we don't have a match again this one's blue and circular and that's not going to fit our particular hormone And in this case, third time's a charm. And so these hormones are going to bind with the receptors on this particular target cell.
And so that's going to communicate this cell and tell it to do some function or effect. That could be a lot of different things. It could be to tell it to create some new proteins.
It could be to tell it to divide. It could be to tell it to perform some other action in the cell. But the main thing here is that this hormone has now communicated with its target cell right here.
Now once that happens and that information has been transmitted, those are just going to continue traveling through the bloodstream. They'll eventually get recycled, they'll get destroyed, or maybe they'll hit another target cell later on. Again, don't forget to look for the two cells we need for any hormonal communication to occur. We have to have a gland that secretes the hormone, and we also have to have a target cell with the correct receptors for that hormone. This type of endocrine communication using hormones is for polar hormones.
Another way to think of that is a hormone that has a charge on one side or the other. They're not going to pass through cell membranes because they're polar and cell membranes are nonpolar. So if you look at our example here, it never passed through a cell membrane. First, exocytosis happened and the hormones were released that way. They never passed through the cell membrane.
They were just released outside. It passed through gaps in the capillary, so it didn't have to go through any cells to do that. And then finally, it binded with receptors on that. outside of a target cell.
It didn't have to enter the target cell and cross that target cell's cell membrane. So this is for polar hormones, and in this case, those never had to diffuse across the membrane. Some examples of polar hormones could include growth hormone, which your pituitary gland in your brain secretes to tell your bones and your muscles to grow, or insulin, which your pancreas will use to regulate blood sugar. Last, we have endocrine communication using nonpolar hormones. Non-polar hormones, you can think about them this way, that they don't have a net charge on one side of the molecule or the other.
This is going to allow them to pass through cell membranes, which was different than polar hormones. I'm going to draw another diagram similar to the last one. This time I'm going to put the secreting cells up on the top right of my diagram, just because I don't want you to have the misconception that the secreting cell is always on one side and the target cell is always on the opposite side. In this case, you'll notice one difference. these hormones are not contained within a vesicle.
They're just floating there in the cytoplasm. They don't need a vesicle because they don't need to undergo exocytosis. They can actually just pass through this membrane.
Because they're nonpolar and a membrane of a cell is also nonpolar, it's made of lipids, those will be able to pass through and diffuse through just on their own. Another thing that you'll notice different on this diagram that I drew is I'm going to draw the nucleus of the cell with some DNA inside of it, some DNA strands there. And also the receptors for hormones are going to be inside the nucleus or on the nucleus, but either way they're inside the cell.
The reason that this can work is because these hormones are nonpolar, meaning they can pass through or diffuse through this lipid membrane. And so let's take a look and see what happens. So I've got a few hormones that are going to pass out of the secreting cell, and they're going to travel down the bloodstream, and eventually they're going to make their way down to a potential target cell.
And they can diffuse through the membrane of that potential target cell, and they can try to bind with the receptor. In this case, this receptor does not fit that hormone, so no communication will occur there. But now if those hormones travel a little bit further down, and they diffuse into this cell, then we will have an effect. Again, that effect could be lots of things.
It could be to tell the cell to produce some new protein. It could be to tell the cell to divide. It could be to tell the cell to perform some other chemical process.
Some common types of nonpolar hormones would be steroid hormones such as testosterone or estrogen, among a lot of others. Here's a quick recap. We talked about hormones and how those are a chemical messenger for one cell to communicate with another cell. We talked about several ways that this can happen.
Autocrine signaling, where a cell releases a hormone and it binds with its own receptors. Pericrine signaling, where an adjacent cell will release hormones to bind with the cell that's nearby. We talked about endocrine communication with polar hormones, where hormones will go through exocytosis, travel through a blood vessel, and then eventually bind to receptors on the target cell's membrane. And finally, we looked at endocrine signaling of nonpolar hormones.
These have no charge, so they can pass through a cell membrane. They're going to pass through the blood vessel, and they're actually going to go through the cell membrane and then into the nucleus of their target cell. will bind with receptors in the nucleus that will cause an effect.
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