[SOUND] Welcome, we're going to continue talking about mammary structure and, particularly, microstructure of the mammary tissue. And we're going to focus in this video on alveoli, and think about the environment of the alveolis actually in the tissue. So let's kind of review kind of the process that we've been going here. From the macrostructure, the whole mammary gland on the animal, down to the microstructure, the histological level. We're going to start focusing on individual alveoli, and then working at this level, so this is kind of the level that we're working with. But before we get started, go to the next slide, want to do a quick review. And we want to talk or think about these lobules and so this whole thing might be one lobule. And remember that we talked in a previous video about the idea that these are really tubes. So again if we cut this in cross section, we actually get a circle. And that's really kind of what we're looking at here, in this particular case, some of these are, for example this one, is connected. And that would essentially be where we've done this and cut through the section this way so that's why you're seeing something that looks like it's not just a circle and it depends upon how the tube is cut. They branch off, there are many of them in the lobule and again when you cut it, a thin section like this through that and get a two dimensional representation. A lot of times you're kind of looking at a circle, so we're going to be looking at wall of that circle, the middle of that being the lumen. Let's go to the next slide. Here's another again example, so this whole thing would be part of a lobule, all these tubes would be interconnected here, let's go to the next slide. So just kind of to remind you some orientation, again, the blue line here represents, I've just kind of changed the color of this so you can kind of emphasize a few things. The blue line here represents the outer boundary of the lobule. Single layer of epithelial cells, we'll get back to that in a moment on the aveolus. Yellow I've kind of indicated as the lumen, so let's get some more vocabulary up here. So one alveolus, multiple alveoli, this has a lumen, and we've indicated that here with the yellow. The red in this case would be the capillaries. Our blood vessels, so someone here, there's one up there. kind of tried to mark out a few of the capillaries here in red. Again, a single layer of epithelial cells. And those are the cells that are going to be producing the colostrum or the milk, whichever the case may be. And again, just going deeper and deeper, looking more carefully at this. And so what I want to really focus on here is one alveolus. And in this next slide, I've put a boundary around that, a yellow line around that just to indicate what we're talking about here, so again, this is a single layer of epithelial cells. The slides I've been showing you here so far in this video and the next, I think, a couple slides here are actually a prepartum tissues. So, it's not quite making milk yet, the darkly stained material in here would be, essentially, colostrum. The white specks in here are fat droplets out in the lumen of colostrum. Again, it looks like there might be multiple layers of cells, in fact, what it is, is a lot of times they are kind of like this. And so each one eventually, when it fills out of milk, I'll show you a picture out here in just a moment. These will kind of flatten down and go from this to this and so they're all each one of these cells is attached to the basement membrane which we can kind of think of as this yellow line here. So they're all actually physically attached by proteins that are linking them to that basement membrane. And We'll get back to that here in a few moments. Next slide, this is an example of one which in fact would be lactating, this is an early lactation cow, but again this are all bovine pictures. Again, single layer of epithelial cells, you can see they've kind of flatten down. So instead of being kind of like this, they flatten down a bit, spread out a little bit. The lumen is much, much bigger because there's a lot of accumulation of milk in this case. Again, lots of the white things here, all these over here are fat droplets out in the milk. And again, we're going to just keep focusing in, focusing in, so some of the slides I'll show you now are just kind of looking at a section like this. So what I want to focus on now are this idea that the blood vessels in the mammary tissues, the capillaries. Again, this is a pre partum tissue here, single layer of epithelial cells, even though it doesn't look like it's a single layer. Lumen, the stromal tissue out here, with Again, the stromal tissue is going to contain all kinds of cells, fibroblast, for example, leukocytes, plasma cells, which are a different kind of leukocyte. And blood vessels and capillaries so we have a little arterial right here, probably a venule up here, capillary here, and what I've done in the next slide is to kind of color some of those in with red just kind of, you see, again this is an arterial. This probably either a lymphatic vessel or a venule seen a nice capillary right here running along, probably continues here. And those are running along the outside of the alveolus, go to the next slide. And here, I've done, indicated, it's the same image, just higher and higher magnification going from low magnification to high magnification. kind of looking at this arterial here, see the red blood cells, these darkly stained materials. There's a leukocyte, white blood cell right in there. Again, going down to a little bit lower magnification, and then this is what it would look like in terms of a very low magnification, how it sits in with all these alveoli, it's in the lobule. Again, just kind of give you an idea of the environment, these alveoli. And they can be sitting right next to the venules as well as capillaries. And just one more image here, again, an alveolus here's a cross-section through a capillary, it actually, looks like a smiley face there, some red blood cells. The capillary goes like this right around the outside of that alveolus. So what we have here, this is some video taken of a lactating rat, so again, taking the, dissecting the skin, actually putting the camera on the microscope, right directly on the tissue of the lactating rat. Each of these circles, kind of yellowish, greenish circles, is one alveolus. So there's a whole bunch of alveoli in here, but the key I want you to look at very, very carefully are the capillaries. You can see the red blood cells running through them, every once in a while you can kind of see one kind of blips or hesitates and something bigger goes through it. That's probably a lymphocyte or a leukocyte of some sort, lymphocyte or PMN or whatever the case may be, and so I just want you to kind of watch that. So this video was taken by Steve Davis and his crew in New Zealand. So just kind of watch the blood flowing through, constant flow of blood going through, around the capillaries. [SOUND]
