[SOUND] In this module, we're going to talk about lactation, and this course is about lactation. So we're really going to focus on what happens in the mammary gland during this process of lactation. We're going to introduce several concepts here. And so we just kind of want to set things up because some of the other videos in this module will go into more detail into some of these concepts. But just to remind us where kind of we are in that lactation cycle, that mammary gland development cycle. Let's go to the first slide to remind ourselves. Again the mammary gland's going through a variety of steps of mammary development. And with genesis, lactogenesis, we talked about that in the mother-neonate module. Again the initiation of lactation. And so finally we're getting here in terms of talking about the process of lactation. And one of the concepts I'm going to really hammer home is the idea that in order to maintain lactation, in order to keep this process going, you've got to remove the milk. Somehow that milk has to come out of that mammary gland and again, we'll investigate that in more detail, but what I'm kind of getting at here, is what happens when you do not remove the milk from the mammary gland. After some period the gland starts to under regression or involution. So in this module we're not only going to talk about lactation, we're also going to talk about mammary gland involution. And the processes involved in that as well. So let's go to our next slide. So I want to go back and remind ourselves of some definitions here. And so the first one, again, to remind us of mammogenesis, the word mammogenesis relates to structural growth and development of the mammary gland. And certainly that's occurring in the prepubertal period, postpubertal period, pregnancy, etc, etc, and in lactation. So mammogenesis is occurring or continuing to occur during the lactation process. So it's going on during this and again, it's a lot of species variation in just how much mammary development's occurring during that period. Lactogenesis is the initiation of lactation. So in order for lactation to happen, you've got to have lactogenesis occur first, and then how do you keep it going after that point? And that's really what we're talking about here in lactation. Let's go to the next slide. Some other definitions to remind ourselves of. Milk secretion. Milk secretion is defined as the synthesis of milk by the mammary gland, by the mammary epithelial cells. So inside those cells they're synthesizing all the different components. The fat, the protein, the lactose, etc. Different kinds of pathways. And then the actual passage of the milk from the cell, and these different pathways, into the alveolar lumen where it becomes milk. After all these different components are mixed together in the alveolar lumen, that's when it becomes milk. So it's not just a synthesis in the cell. It's the process of those components getting out of the cell into alveolar lumen at which point it becomes milk. So that's referred to as milk secretion. Sometimes we also use that word, so milk secretion in that sense is a verb, it's an action word. Sometimes you also use that it's talking about secretion from the gland itself, from the entire gland. And that wraps us back into this word milk removal, I'll get to in just a moment. The other time we often sometimes use this word secretion is as a noun, so milk is a secretion from the mammary gland, colostrum is a secretion from the mammary gland. So you have to kind of think about how are we using that word and this definition is really at the cellular level, the tissue level in terms of synthesis. And then secretions of the mammary gland, we have an entire module on that particular topic. Milk removal, passive removal from the cisterns, of course it depends upon whether the species has cisterns or not. So cows and goats and sheep for example do have a cistern, remember in the cow, the teat has got a big cistern in it. The gland cistern, big cisternal ducts. Pigs do not have a cistern, really to speak of there's nothing substantial. The human breast does not really have cisterns. So it depends upon the species as to whether you get very much of the passive removal of milk. Milk removal also involves ejection of the milk from the alveolar lumen. That's the milk ejection process. Again, we have a whole module on milk ejection. And so it has nothing to do with the milk getting pushed outside of the cell into the lumen. That's this up here. But milk ejection is then squeezing the milk, those myoepithelial cells contracting around the alveolars, pushing the milk down through the ducts and hopefully eventually out of the nipple or the teat. But also then to add to that removal of the milk from the gland, because we can have milk ejection in the absence of removing the milk. So the milk ejection process can happen, if you don't actually remove the milk, eventually the myoepethelial cells relax. The milk kind of, some of that milk goes back up into the ducts in the alveoli. So you can have that. So in order for milk removal to occur, you literally have to remove the milk from the gland, get it out of the gland. That then comes into the word lactation. So what's the definition of lactation? Combined processes of milk secretion. That's this up here. And milk removal that we just talked about. So it's the whole thing, making the milk in the cell, secreting it under the lumen. It becomes milk at that point. And then milk ejection to get it out of the gland and then actually physically getting it out of the gland. And again that milk removal part's really important for maintaining lactation which is galactopoiesis. Again that idea that galactopoiesis is the word we use for maintenance of lactation. So once you get it started with lactogenesis, you gotta keep it going. And the way you keep it going is removing the milk from the gland. That's part of the process, there's certainly other things involved as well. [SOUND]
