[SOUND] Welcome back, so let's continue our discussion about mammary structure. One of the key models we're going to use is the dairy cow, and as you go through the various videos you'll kind of see why we're using that as one of our key models. But what we want to do before we start getting into the kind of pictures and details of the mammary gland structures. Let's go back to the farm and look at a cow and think about what does this udder look like? What's going on there with this udder in terms of structure and a little bit in terms of function? So what we're going to do now is we're going to head out to the dairy farm and take a closer look at mammary structure on a cow. So we are back at the University of Illinois Dairy Farm, at Dairy Research Center. And again, we've been using this particular species as one of our models. And what I'm going to do with her today is just kind of very briefly review mammary anatomy and the gross anatomy in the mammary gland. So remember that the mammary gland is a skin gland. That means it's outside of the body wall. That means we have to be concerned about things like how does the blood get into the mammary gland? How do the nerves leave and all those kinds of things and take a quick look at that. We just want to kind of take a look at that on her here. This cow is about seven and a half years old. She's probably in about her fourth lactation at this point. And she's been lactating for several months at this particular point. So first of all, again, the mammary glands a skin gland, it's outside the body. She has four glands we call this an inguinal region down here, back in this area. [COUGH] The four glands are Independent of each other. So there is a left half and a right half and then rear quarter and front quarter. If we were actually to go in here and surgically remove one of the halves, we could do that successfully. It wouldn't be that easy but we could do that successfully and the other half should still function perfectly fine. On the other hand, their front and rear quarters, where they come together. If you took a cross section through here, you really couldn't see a demarcation between the front and rear quarters at that point. Another part of the mammary gland that's really critical, especially on an animal like this is called a suspensory system. There are multiple layers to the suspensory system and we'll talk about those here in a second. But just to give you a perspective on this an empty mammary gland such as this might weight, say, 50 pounds or 25 kilograms just empty. If the cow's producing 100 pounds of milk a day and she's milked twice a day that means when she enters the parlor she's got 50 pounds of weight that's in the gland plus 50 pounds of milk that's in the gland. That's 100 pounds or roughly 50 kilograms of weight hanging down from the body. So the suspensory system is really critical to make sure that gland stays up tight to the body. [COUGH] So what are the layers to the suspensory system in a cow like this? Well, the most obvious ones and one's that don't have don't. Keep up very much with the weight is the skin and the fats that is right underneath the skin. Obviously those are lose, they're not going to do that much for pulling all that weight against the body. The next layer in though and there is actually two layers, there is a superficial and a deep layer that is called the lateral suspensory ligament. Lateral being on the sides it comes down from the pubic bone down here about like that. The deep layer actually sends projections into the gland, is fibrous and so it kind of holds the gland on its side. The other part of the suspensory system which is really, really critical is called the median suspensory ligament. It's going to be right here in the middle. It's going to be attached to the body wall and then come down between the left and right halves. Its, it's about that wide at the top and maybe a little bit wider than that then it kind of flanges out between the left and right halves, that's elastic. So as the mammary gland fills with milk during the time between milkings the mammary gland of course is coming down, the weight is pulling it away from the body a little bit. That elasticity allows it to do that without going too far. The fibrous lateral suspension ligaments keep it held up to the gland. If we actually took different ways, if we sacrificed this cow, we set her up, we took the legs off, we took off the different layers down to the only thing that was left attaching the body, the mammary gland to the body was the suspension ligament the gland would still hang there almost perfectly balanced. Which is really, really kind of cool. So again, that main suspensory ligament is really critical. When that main suspensory ligament weakens, what happens is you start getting a flat bottom on the cow here. You can see a nice groove between the left and right halves right there and that gets kind of flattened out. That starts to pull the gland away from the body. And so that starts to compromise the blood vessels, the nerves, and so on and so forth, the lymph vessels that are going up out of the gland into the inguinal canal. [COUGH] So let's focus a little bit more on the bottom of the mammary gland. That is the teats down here. Again, there's one teat per gland. And for the cow she has one opening called the streak canal that comes out the teat, it drains all the milk in this gland. This has a separate teat and a separate streak canal. The front one's do as well. So the milk produced in this gland only comes, this quarter, this teat, the milk in the front quarter only comes out that front teat. It doesn't cross over. You see the milk collecting systems are completely separate between the glands. [COUGH] Inside the teat, we have the teat cistern, it's an open area, right above that is called the gland cistern, so that'll be right in here. That's again an open area, and then the major cisternal what you call cirternal ducts, and again they can be as big as my finger in that case. And there's a ducts that's are projecting up into the mammary gland, the main ones draining out all the milk. So the milk comes down, it's in the cisternal areas, the cisterns, the teat cistern, and then during milking that fluid can come out. The, again, there's only opening per teat for this species, the same is true for goats and sheep. Pigs on the other hand, for example, have two openings per teat. So in that case they actually have two glands and each of them sends out one projection, one in science is what it's called, coming out of the nipple. Other species have multiple, like our own species, nipples on humans have ten to 20 openings per gland. So it's just depend upon the species, and how the gland develops from the fetal stage on. Another important part of the mammary gland is blood flow going to the mammary gland. Very highly metabolic reactive tissue lots of lots of milk will have to go through. So they talk about approximately 500 units of blood going through the mammary gland for every unit of milked produced. So if a cow's producing say in an hour to eight hour period, which is milk three times a day in an eight hour period, she's producing about 25 pounds of milk a day, during that eight hours, excuse me. Times 500, and that's about 3 gallons of milk roughly and that calculates out to about 1,400 gallons of blood went through this gland to produce those three gallons of milk. So, it's very, very important is the circulatory system of the mammary gland. What we have is up in this area, there's called an inguinal canal. And through inguinal canal comes an artery and vein. It's called external pudic or external pudendal artery and vein, come through. Once they get down to the mammary gland here they split and go in both directions. And in some projections arteries down and then, of course, the veins follow back up in parallel with that going in the other direction. There is a small vein or a small artery comes out the back here called the peroneal artery and there's a respective vein. It only sees just a little bit of the back of the mammal gland here. Particularly to the cow, this is vein right here, this is called the milk vein. Great pink torturous vein that comes out from the gland It does not produce or secrete milk. It's not carrying milk. It's carrying venous blood. There is not a particularly similar sized artery that's feeding the mammary glands. It's probably one similar to this feeding the rest of the skin. This is technically called a subcutaneous vein coming out here. Subcutaneous abdominal vein coming out of the front of the mammary gland. This is important because when she lays down all that weight redistributes how the blood is flowing into and out of the gland. So this is an extra exit for the venous blood coming out of the mammary gland. Another part of the mammary gland is the lymph flow from the mammary gland. This is again, a very highly metabolically active tissue. Lots of blood flow going through there. So there's lots of fluid going back and forth in the tissue and so some of that's coming out as lymph. So there's a huge lymph system. Lymph drainage, remember lymph drainage is only one way, it's not like blood that's going both ways, arteries and veins. There's only a one way system going back into the body. The lymph vessels come up here to the, there's a supramammary lymph node, supra meaning above the mammary. A great big lymph node right up here. In fact these are, you can actually see a little bit of the outline of these guys right here. And then those have vessels going back into the mammary gland. So lymph drainage is very, very important. When we talk later on about edema in the mammary gland, where lymph drainage is not sufficient to take all the fluid away. Especially when the animal's just, when she's just calved or when animal's just have their young, the mammary gland can retains a lot of fluid and that's part of that reason is because the lymph flow is not adequate. So let's briefly think about the nervous system and the mammary gland. The alveoli, the ducts and those kinds of things are not innovator. Remember, they contract in response to oxytocin. The myoepithelial cells contract in response to the hormone oxytocin, not to nerve impulse. Nevertheless, nerve impulses are critical this. So remember for milk ejection, we had the nerves going up from the teat and going up to the, sending action potential up to the brain and causing oxytocin release. We have a lot of blood in here so those blood vessels, especially the arteries, have innervation to them, sympathetic innervation to those. But that's pretty much all the innervation that's inside the mammary gland. [SOUND]
