 Now, I want you to take a second. I mean, we've got transporters. We have this visual of, let's just, I'm going to take a little bit more time, but sometimes I draw my transporters as circles. That lets you go ahead and visualize your, you know, your whatever shape it's going to be. Is it a channel? Is it a transporter like this? Different flavors of transporters. But sometimes you don't have to draw all the crazy details. I usually try to remember to draw my cell membrane with two Y. Why are there two lines representing that cell membrane? Because that's actually my phospholipid bilayer. And I'm drawing it this way for you so that you can see that sometimes, this is familiar to you, dude, really? Why don't I just draw a couple of boxes? Dang it. I'm going to have to mess with it anyway. What else did I just draw right here? Ignore all this stuff in the middle. Okay, like that. I should draw two transporters. And, okay, usually there's no way on the planet I'm ever going to draw my double layered thing. What in the world am I drawing somebody? Please send some help. What is this? Okay, this is a cell. And guess what? It's a cell lining your intestinal tract, which means that this is the lumen. Aren't you happy you had anatomy? Piece of cake. You know that epithelial tissue, so I'm just going to make a little note that this is an epithelial cell. Epithelium lines the lumen. This is probably a simple cuboidal cell. This is my, I'm going to have some connective tissue down here. And ultimately, if I'm going to absorb a molecule, if I'm going to get something from the outside and the lumen into the cell, if I want to get that thing, for example, into, let's just say, the bloodstream, this is a blood vessel. Of course it is. If I want to do that, how many cell membranes am I going to have to pass? Two. Actually, I'm going to have to pass another one, because I'm going to have to pass through the cell membrane. I'm going to have to pass through another layer of epithelial tissue. Okay, so the whole point is we don't, often we'll just transport molecules in and out of the cell, but often we have to transport molecules across layers of epithelial tissue. Usually the tissue is simple when we do that. Usually it's just one layer of epithelium, not a problem, bring it in, cross two cell membranes to get it in, cross two more to get it into the lumen of the blood vessel, and now it's in the blood. Now let's take it somewhere, if we want to go backwards and dump whatever that was that we just absorbed into a responding cell. We're going to have to do that. Now to start your lunch, we're going to have to cross two more layers of epithelium. We're going to have to cross out of the two layers to get two more cell membranes. In order to get into the interstitial fluid, two more cell, one more cell membrane, to get into the cell itself. Did you even, like, that's called epithelial transport, and it's, you don't want to forget that to get things inside our body, we're going to have to transport them there. Transporters will diffuse right in, but often we have to have transporters, and we can team up our transporters in different combinations to get this to happen. Over and over, we're going to see it, and we're going to identify our different transporters and then go, yeah, that totally makes sense that if we have those transporters in those places, we would get the movement of molecules basically completely through the cell to enable absorption. Okay, there's one more form of transport that we didn't talk about, and that's phagocytosis. This cell itself, or endocytosis or exocytosis, the cell membrane itself can actually, like, create a little bubble. Do you see what is happening here? And then it pinches off, and whatever was outside is now inside. This concept is pretty standard, but we're going to see that, yeah, this is going to be important in understanding physiological function. Oh my gosh, that's it for the lecture on transport. Next up is how cells communicate with each other. That's exciting.