Breast anatomy and lactation

- [Voiceover] Lactation is a process where milk is made and ejected from the mammary glands inside the female breasts. Besides being really nourishing for a suckling baby, breast milk can also boost a newborn's immune system because it contains antibodies that the baby can't yet make on its own. But overall, breast milk supplies all of the nutrients that a growing infant needs for the first six months of life. So before we look at the mechanism of lacation, let's just get oriented to the anatomy of the female breast. So this is a woman's left side here. And here is her left arm raised up in the air. And this here is her pectoralis major muscle. And the pectoralis major is the primary muscle of the chest. And the reason I mention the pectoralis major, or the pec major, is just because the breasts on the left and right side overlie the pec major on the left and right side. So it's just to give you a clearer idea of where exactly the breasts lie in relation to the chest wall. And so what I've done here is I've cut away the overlying skin on part of the breast so we can look at deep structures on the right side of the breast and we can look at superficial structures on the left side of the breast. And remember, I mean right side and left side from the perspective of our lady here. So the breast in both females and males contains special glands called mammary glands. And mammary glands are actually modified sweat glands that are able to produce and eject milk. So in women they develop around the time of puberty and in men they actually don't get developed. They stay pretty benign. And actually, before pregnancy, the mammary glands don't really make up a huge percentage of a woman's breast. But during pregnancy they sort of expand and branch out in a big way in response to stimulation by hormones such as estrogen and prolactin. And so they're actually a little bit tough to see on this drawing here. So I'll just blow them up for you a little bit. So we can get a better look at the anatomy of a mammary gland. So these mammary glands, surrounding them, almost like a net encasing them, there are these cells called myoepithelial cells. And the myoepithelial cells are special cells in that not only are they lining the outside of the mammary glands, but they also can contract and squeeze down on these glands to squeeze milk out of them. So milk is drained toward the nipple through ducts called lactiferous ducts. And from there the milk can be ejected out through the nipple, through these tiny holes all over the nipple called nipple pores. And so let's take a look at what this would look like on the bigger drawing here. So we've got our myoepithelial cells lining the outside of these mammary glands. And then they'll squeeze milk out of the mammary glands. Send the milk along the lactiferous ducts, toward the nipple, and remember this is happening in all of the mammary glands, and then it's ejected out of the nipple through tiny holes in the nipple called nipple pores. And actually, let me label this as a lactiferous duct here. And while we're in this nipple area, you might notice that that there are these dark, circular areas around the nipples. They're called areolae. And the areolae serve a couple of different functions. The first one is that they contain these little bumps called the areolar glands, or Montgomery glands, that's the other name for them, and the areolar glands secrete a bit of an oily substance called lipoid fluid. And the lipoid fluid moisturizes the nipple so it doesn't get dry or cracked during breastfeeding. The second function is more for the baby's good. It turns out that the darkened areolae sort of give the infant a target, something to aim for. They actually don't have the best vision when they're born, so this helps them to find their food source a little bit easier and quicker. And actually I forgot to mention, there's some research that suggests that the lipoid fluid made by the areolar glands, that it has a certain smell that attracts the baby as well. So the areolae serve a couple different functions. The breast also has a fair amount of fatty tissue, or adipose tissue, making up most of its content. The fat actually also supports all of the glandular structures we've mentioned. So with all of this stuff going on in the breast, the glands and all of the fat, it can get a little heavy, especially when the mammary glands are full of milk during lactation. So it needs these special suspensory ligaments, also called Cooper's ligaments, that help it remain anchored to the chest wall. And that's what you see here in green. So now that we've looked at the major anatomy of the breast, let's get to what happens in lactation. Lactation begins when an infant begins to suckle on mom's breast. But let's take a closer look, because there's some pretty cool neural pathways that are involved. So when a baby starts to suckle, special receptors called mechanoreceptors in the nipple, they get activated and they start to send messages up the spinal cord and into mom's brain, to the hypothalamus. And at this point, the hypothalamus, when it receives these messages, it does two really cool things. It sends on signals to a set of oxytocin neurons in the posterior pituitary gland, telling them to make oxytocin. And so here you can see oxytocin being produced. And the hypothalamus also sends an off signal to a special type of neuron in the anterior pituitary that releases a hormone called prolactin inhibiting hormone. And these neurons in the anterior pituitary are called PIH neurons. And they have a bit of a funny job. So, as their name might suggest, they inhibit other neurons in the anterior pituitary from producing prolactin. So since they hypothalamus has turned them off, now the prolactin neurons in the anterior pituitary are free to make prolactin to their heart's content. And you can see them producing prolactin here. But why is this important? Well, it's important because prolactin causes the mammary glands to start producing milk. And oxytocin stimulates these myoepithelial cells that surround the mammary glands, oxytocin stimulates them to eject the milk out of the nipple so the baby can be fed. So you kinda need both of them to have proper breastfeeding. And interestingly, I said at the beginning that it is the suckling of the baby that sorta kicks off this whole neuronal cascade to cause the let down of milk, but remarkably, even the sound of a baby's cry and it doesn't have to be mom's own baby, it can be the baby of a complete stranger, but when mom hears the sound of a baby's cry her hearing centers in her brain will actually trigger this cascade from here. And will cause milk creation and ejection. And this mechanism sorta evolved as a safegaurd for our babies. To ensure that crying babies could still be fed by other lactating women, even if their own mother wasn't around, so that they could still grow and stay healthy.