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Vishal Punwani 创建




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 newborns immune system because it contains antibodies that the baby can't yet make on its own but overall breast milk supplies all the nutrients that are growing infant needs for the first 6 months of life so before we look at the mechanism of lactation let's just get oriented to the anatomy of the female breast so this is a woman's left side here and here's your 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 mentioned the pectoralis major or the PEC major is just because the breasts on the left and right side over lie the PEC major on the left and right side so it's just to give you a clear idea of where exactly the breasts lie in relation to the chest wall and 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 contain special glands called mammary glands and mammary glands are actually modified sweat glands that are able to produce and eject milk so when 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 breasts 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 Oh 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 is elective force duct here and while we're in this nipple area you might notice that there are these dark circular areas around the nipples they're called areola and the area only 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 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 areola sort of give the infant at 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 by the areolar glands that it has a certain smell that attracts the baby as well so the aerial they 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 breasts the glands and all the fat it can get a little heavy especially when the mammary buns 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 are 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 to spinal cord and into mom's brain to the e 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 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 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 the hypothalamus has turned them off now the prolactin neurons in the anterior pituitary are free to make prolactin to their heart's content and 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 it 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's the suckling of the baby that sort of turret kicks off this whole neuronal cascade to cause the letdown of milk but remarkably even the sound of a baby's cry and 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 sort of evolved as a safeguard for our babies to ensure that crying babies could still be fed by by other lactating women even if their own mother wasn't around so that they could still grow and stay healthy