welcome to the lab everyone I'm Jonathan benan with the Institute of human anatomy and today we're going to talk about why breasts are so important now we all may have some different reasons as to why we find breasts important but here at the Institute of human anatomy we're going to talk about why breasts are important from a biological and reproductive standpoint the science of breasts if you will and of course give props to all the moms out there that have utilized these anatomical structures to plump up babies deliver them antibodies and all sorts of cool things that are found in breast milk so on top of talking about the anatomy of breast we'll also talk about the physiology of milk production and breastfeeding as well as the ingredients of breast milk and yes we will also talk a little bit about the Aesthetics of breasts is there definitely is some interesting Anatomy that people are curious about when it comes to procedures like breast augmentations so let's get into this so let's start our story about the breasts by taking a look at A sagittal pelvis this is a cut through the midline of a female pelvis so this would be a cut here and looking into the right side and here we have the vaginal Canal the right half of the uterus and even an ovary right here now you might wonder what do these pelvic structures have to do with the breast well during puberty estrogen released from the ovaries increases dramatically estrogen has many incredible functions including promoting the development of female secondary sex characteristics and one of the those secondary sex characteristics is the development of breast tissue the breasts are hemispheric projections that can be quite variable in size and are made up of mamory glands connective tissue and adapost tissue which is just fatty tissue and the increased in estrogen during puberty stimulates the growth of the mamory glands as well as promotes increased deposition of fat and all this increases the overall size and mass of the breast during puberty the breasts are on top of or superficial to this muscle called the pectoralis major and even cover a portion of this muscle on the side called the seratus anterior and we'll talk a little bit more about this relationship with the pectoralis major specifically when we mention some information about the different types of breast augmentations in just a minute but the breast attached to these muscles with a layer of fasia and are also supported by connective tissue strands that run from the fascia to the skin called suspensory ligaments of the breast also known as Cooper's ligaments and what's interesting is that these ligaments do become looser with age which contributes to the sagging of the breasts as the female gets older and they can also become looser with excessive strain that could occur with long-term jogging or other high impact activities and this is why wearing a sports bra can help to maintain the Integrity of these ligaments and as I already mentioned there is a mamry gland within each breast which is actually a modified sweat gland that produces milk each mamry gland is made up of about 15 to 20 loes which you can see one of those circled in this picture these loes are separated by variable amounts of adapost tissue and this variable able amount of adapost tissue is one of the things that contributes to the variability in overall breast size each lobe within a mammory gland is made up of even more compartments called lobules and if we were to zoom into one of these lobules we would see that the lobules are made up of these grape like structures called alveoli and these alveoli are aligned with the milk secreting epithelial cells and so just to kind of step back here each breast has a mammory gland each mamry gland is broken up into 15 to 20 loes and each loobe is made up of multiple lobules and each lobule is made up of these multiple alveoli which actually contain the milk secreting cells so that explains all the hardware or structures necessary to produce and secrete milk but obviously the breasts aren't producing milk all the time that is normally reserved for breastfeeding during pregnancy there's this wonderful gland located in the center of your brain that you can see here called the pituitary gland and just to orient you this is A sagittal cut through the head so cut like so and if you were to go straight back from the Bridge of your nose you'd run into this pituitary gland and specifically the anterior portion of the pituitary gland will release a hormone called prolactin and as that name implies prolactin will stimulate lactation the prolactin levels will steadily rise from about the fifth week of pregnancy until birth by which time the prolactin levels have risen by about 10 to 20 times that of the normal prolactin level seen in a non-pregnant female at the same time during pregnancy the placenta is secreting large amounts of estrogen and progesterone which causes even further development of the breasts by causing the milk ducts to grow and Branch as well as causes even more fat to be deposited within the breast and anyone who's been pregnant before definitely notices these changes as an increase in breast size what is very interesting about the estrogen and progesterone is that even though these hormones further promote the growth and development of the breast during pregnancy they actually inhibit milk secretion in a way blocking some of the effects of prolactin and because of this inhibitory effect for most pregnant females zero to no more than a few milliliters of fluid are typically released from the breast per day until after the baby is born because once the baby is born the placenta is also birthed and therefore is no longer inside of mom secreting that extra estrogen and progesterone that was inhibiting the release of milk so now all that builtup prolactin can take effect allowing the baby to have their own personal set of lactation station a few days prior to and a few days after birth the fluid secreted from the breast is called colostrum which contains similar concentrations of proteins and lactose as the milk but almost has no fat however it does contain antibodies white blood cells vitamins minerals and growth factors which are important for supporting the newborn's health and protecting the newborn from infection over the next week the breast will start to produce large quantities of the typical breast milk instead of the colostrum and we'll get a little bit more into the contents of breast milk in just a second but let's quickly talk about milk ejection or what is often referred to as let down and this is pretty cool how this works milk is continuously being secreted within the alvite of the mamory glands that we learned about earlier but the milk does not flow easily from the alveoli and into the ductal systems of the breast so when a baby first starts to suckle the baby receives virtually no milk for the first 30 seconds or so but then sensory input from Mother's nipples are transmitted through nerves to the spinal cord and those signals will move up the spinal cord and make it to this structure here called the hypothalmus and the hypothalmus will tell the posterior pituitary gland to release a hormone called oxytocin and tell the anterior pituitary to release more prolactin so now both of these hormones will be circulating in the bloodstream but again it takes about 30 to 60 seconds for these hormones to make it to the breast tissues prolactin will continue to promote the production of milk within the alveoli but when the oxytocin makes it to the breast it will cause these cells that surround the outer walls of the alvioli called myoepithelial cells to contract and this contraction causes the milk to move from the alveoli and into the Ducks so the milk can now be expressed and available to the baby and this is referred to as milk ejection or let down now some other things that are interesting to note is that suckling on one breast does not just affect that one breast it will also have the same effect on the opposite breast so milk will be available in both if suckling starts on one side versus the other and coming back to this hypothalamus that we mentioned earlier one of the functions of the hypothalamus is to regulate certain motions and so this explains why fondling of the baby by mother or hearing the baby cry can result in an emotional signal being processed by the hypothalamus which can also result in the same process of milk let down to occur so what is the composition of breast milk well human milk is about 88. 5% water 3. 3% fat 6.
8% lactose which is the main carbohydrate in milk 0. 9% casine the main protein 0. 4% of lactalbumin and other proteins and 0.
2% of Ash which is the minerals such as calcium and it is interesting to compare this to the composition of cow's milk and looking at this chart there are components that are pretty close but there are also some significant differences such as human milk has about 50% more lactose than cow's milk but the protein content in cow's milk is more than two times greater also of importance is the immune support that breast milk can provide as there are antibodies found in the milk which would be part of that other proteins category that we saw in the chart because antibodies are actually proteins there are also several types of white blood cells that are in the milk such as neutrophils and macras some of which are especially lethal to certain types of bacteria now we should also just thank mom from a calorie standpoint because Mom can burn anywhere from 600 to 750 calories a day just producing milk this can be higher depending on how much milk is produced which can be up to 1. 5 L A Day sometimes even more especially in the case of twins so now that we've talked about the functionality of the breast tissue many people that come into our lab are often curious about the anatomy that influences the Aesthetics or the look of the breast specifically regarding the Cosmetic surgical procedure of breast augment ation now the natural shape and size of the breast is mostly influenced by the size of the mamory glands and the amount of atopos tissue within the breast and again that varies from person to person but other things can also influence the look of the breast like strain on those suspensory ligaments obviously age has an influence and even the changes that can occur with pregnancy can change the shape and size of the breast and many of these changes can remain even after pregnancy and breastfeeding is completed and the main thing will'll address with a breast augmentation is the ation of the implant there are two primary placements that you most often hear about over the muscle versus Under the muscle and the muscle that we're referring to is the muscle we talked about earlier the pectoralis major that you can again see that I'm tracing with the probe here now over the muscle is actually called subglandular placement because the implant is placed below or deep to the natural breast tissue but superficial to the PEC major muscle with under the muscle or submuscular placement the implant is is placed deep to the PEC major well at least mostly deep but I'll get into that in just a second now whether a plastic surgeon in the patient decide to put the implant over the muscle versus below the muscle or under the muscle depends on a variety of factors one of those factors being how much natural breast tissue the patient already has because if the patient has a small amount of natural breast tissue putting the implant above the muscle is usually not a good option because this will likely show too much of the implant and you can get Rippling so this person could be a candidate for submuscular placement where an incision would be made along the inferior margin of the pectoralis major in order to create a pocket for the implant and this tends to hide the majority of the upper portion of the implant and give a little bit more of a natural looking appearance however a con to submuscular placement is that recovery from the surgery can be a little bit more painful and you can get some small movements in Rippling on the underside of the implant due to contractions of the pectoralis major whereas you wouldn't get as much of this movement during muscular contractions with sub glandular placement so there are definitely pros and cons to both and why someone would obviously want to have a consultation with a plastic surgeon prior to making any definitive decisions one of the reasons I love the anatomy lab so much is that you do a lot of your learning by doing it's interactive it's Hands-On it's active learning and that's why I want to introduce you 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