[SOUND] I need to introduce you to a concept of a lobe. What is a lobe? So what I've done here is to take, this is actually taken from a rabbit, but I put this together just to illustrate kind of of what concept of a lobe is. In this particular case if we follow this around, this particular structure kind of looks like a tree structure here. You notice that this branch goes off, excuse me, this main trunk of this lobe goes off and branches many, many times. Here's another lobe here. And here's another lobe here. If we put those together with another set, in this particular hypothetical animal, we've got six lobes. So I've drawn in or put in three more of these down here. And you notice again that once this develops, this duct system develops into a lactating tissue. And again this will be maybe very early pregnancy or in a cycling animal. So it's not a very developed animal. But again, anything produced out here in terms of milk would only be exiting through this one dot. Same way here, same way here. So those lobes are independent. The milk collecting system, the milk secreting system of this lobe is independent from this lobe, is independent from this lobe, and so on. So if we then put on a make believe nipple, that's this brown thing and I've kind of indicated it with these black dots here, where the opening in the nipple, is. So in this particular, again hypothetical animal, it would have six lobes, each of those would be independent in terms of its milk-secreting process, and they're going to exit independently through individual holes in the nipple. So, different species have different numbers of glands, different locations of the glands, and different number of holes, or opening in the nipple. So we want to explore that concept here a little bit more. Compare that say with a cow, that last hypothetical animal had six openings per teat. And again it's a hypothetical animal, so we don't know how many nipples or teats it has. In this case, with a cow, what we've done is we've taken the teat in the lower end of the mammary gland, and we've cut it in cross-section, so we have one opening down here, it's called the streak canal. This is called a teat cistern, it's an opening in the teat or the teat is open, and then right above it would be something called the gland cistern. Now the important thins to notice here is that there's holes up here, almost looks kind of like Swiss cheese, all these holes. These are the major ducts or we call sometimes cisternal ducts coming down from different lobes up in the mammary gland. So whereas that hypothetical animal each lobe emptied out through the nipple, and in case of the cow, they actually coming together inside of gland, and then there's one exit for the whole thing. So again, you get these different kinds of teat formation, again, how many exits there are per teat. So this is an example of a cow, a goat, a sheep, many species are going to be like that. Lets take another look at another example. This gets back to our pig. In fact, in each gland in the pig, again she might have six or seven on each side, each gland has two glands within it. So we can think about a complex gland and a simple gland. A complex gland is what you see on the outside. So, in humans, we have two breasts, the pig might have six glands on each side, and you can recognize those, but then the simple gland are how many are inside of each. And in the case of a pig, there are two per complex gland, and you can very nicely see in this particular cross section, what's going to be the lactiferous sinuses going out each side. So, once this develops, and again, this is a very immature there's not really very much, there's no milk being produced in this. But as this develops here, milks being secreted here is going to go out this particular one, and then milk being produced over here is going to go out this particular one. So let's take a little closer look at this. So what I've done here is to take a cell, a mammary gland, and we're going to draw this out, so you're going to get the idea of what I'm talking about here, so this is a gland, a gland that's being nursed by a piglet. This is a gland being nursed by a piglet. This particular one is not. So when the sow has her babies, all the glands are potentially functional. That is, they're all making colostrum, they're all there potentially to make milk. On the other hand, if a gland is not suckle, it starts to involute. These glands are being suckled. This one is not, it is involuted, so the gland itself is very small at this point, so we're going to focus mainly on these two. So again, what I've done is kind of draw an outline here of where the gland is, and again, the idea that inside of this posterior, anterior, there are two glands. So this milk collecting system is going to come out one hole, this milking collecting system going to come out at another hole, and this is what I've done. Just draw in these red lines here and again, so we got two glands and they're going to come out respectively in these holes. So each of these teats has two openings in it, one way we can see that is to actually inject a dye up into one of these, first of all we would sacrifice the cell. We would take the mammary gland off, take a needle and thread it up through the opening, one of the two openings here, inject dye up there, and then cut the mammary gland from the back side, and we can see very nicely. In this next slide, if you look over here, kind of a demarkation here. This is blue, because I injected blue dye in there, and this half of the gland is not dyed. So very very clearly, this part the milk collecting system, the duct work of this is independent from this part over here. To just kind of give you an idea what we've done here, the easiest way to see this, because sometimes on the very tip of the nipple of the pig, it's kind of hard to see those openings. They're there is to actually cut the tip of the gland off. So again, this animal is sacrificed, the gland was taken off, cut the tip off, and you can see very clearly these two lactiferous sinuses going back up into those two respective glands in the mammary gland.
