<What they are seeing now on ultrasound is that the ducts can dilate at different parts of the breast, not just behind the nipple> My understanding of the MER from dairy research is that sporadic dilatation of ductal structures has never been thought to be confined to just the parts behind the nipple. (great similarities in function and microscopic anatomy of all mammalian glands and ducts despite eventual differences between the distal portions of udders/teats and breasts/nipples) I cannot lay my hands on it this minute, but I have a reference with a diagram nearly 50 years old, I believe by Linzell, illustrating his idea of what happens to a duct in any mammal during MER. There are myoepithelial cells not only in a basket pattern around each alveolus, but around nearly all ducts except the ductule (the smallest tubing right off the alveoli). Around the ducts their pattern of arrangement shifts to a combined spiral, longitudinal distribution. Apparently in response to oxytocin, the myoepithelial cells sequentially cause the ducts they surround to simultaneously shorten in length as they dilate in diameter, to propel the milk forward (in a manner that reminds me somewhat of peristaltic action of the GI tract, or a snake digesting a mouse!) That's what constitutes a MER. The myoepithelial cells contract not only in response to oxytocin but also, in response to direct pressure on the myoepithelial cells. (Ever wonder why a calf butts the udder or a kitten or puppy (and many human babies) "knead" mom while eating?) What I remember Dr. Hartmann's answer to my questions about this at several other seminars was that wherever ducts converge in the breast on their pathway toward the front of the breast, the area of convergence of the two (or more) ducts is temporarily a little wider than either of the ducts themselves. His description reminded me of what we experience when on the highway with merging of other routes as they enter onto the main highway - for a short distance until the merging lane is completely funneled into the highway, the roadway is somewhat wider at that point. <and there are no "lactiferous sinuses" as we know them.> Repeat those last four words very slowly, over and over and over. Just because the sinuses are not "as we know them" does not mean that "there are no lactiferous sinuses-period!" It means that it is our "knowing" that is incomplete at this point in time. I assure you, the histologists and breast surgeons placed this term into the nomenclature of the parts of the breast, and have printed actual electron microscope pictures of them. They *do* exist as separate entities of the ductal system in the area of the nipple-areolar complex. Granted, I doubt they are arranged precisely like the spokes on a bicycle wheel as diagrams have led us to believe, but they are there, and are palpable at certain portions of pregnancy and lactation. In the "resting" or non-lactating breast, they are contracted, and their shape is described in very interesting terms, and they are clearly identifiable under a microscope to the trained pathologist or surgeon's eye. There are even certain disease processes that affect just the lactiferous sinuses! What is missing from our understanding, it seems to me, is the process that happens to the sinuses from the time they are seen two-dimensionally under a microscope, contracted, in the non-pregnant breast, until the time they are well expanded in full lactation and "caught in the act of functioning" during these shadowy, still two dimensional ultrasound images. I maintain that between these two extremes are several stages where the "bulging" state naturally occurs. An experienced examiner can palpate them in most mothers from the mid-third trimester onward, and clearly feel their slight bulging throughout the first weeks and months of lactation until they have developed their full elasticity and the contour the researchers describe at that point in time when these ultrasounds have been filmed. < (Branches starting at the nipple similiar to a tree's roots just as Jean described.)> It is fascinating to read how this occurs both in the embryonic development of the breast, and as a result of the menstrual cycles, and especially during pregnancy. Branching is a biologic phenomenon in many organs and is just recently being explained in biomedical literature in terms of physics (fractal geometry - the major blood vessels of the liver are one example.) <Next, to tie this in with hand expressing and pumps; when compressing behind the nipple where the baby's mouth would be, is to stimulate the MER because of the hormones are being stimulated not because one can just squeezes out milk? Mothers should not expect to see milk the first compression with their fingers and should be encouraged to work around the nipple until the milk starts to eject. Right?> Well, my answer is both yes and no. Deep stimulation behind the nipple does seem very successful in stimulating MER, within a minute by direct compression and more strongly in a few minutes as a result of oxytocin. But if the fingers are placed in just the right place, one can expect to see droplets of colostrum/milk immediately in nearly all mothers, well before any MER occurs. That's where I see knowledge of the nature of lactiferous sinuses being of value. Milk transfer has to do with hydraulic pressure, (Pascal's law?) and if compression (of the fingers, or the tongue, or the sinuses against the pump flange) can be focused on just the right area of the lactiferous sinuses, one can boost hydraulic pressure. So, as I said, my explanation to the mothers when I teach them to fingertip express will remain exactly the same: "There is no milk stored in the human nipple. Tiny amounts are stored in little "balloons" under the circle. Imagine them like little toothpaste tubes that you are trying to empty. Remember how you have to start pressing from the far end to get the most to come out?" <This is all so fasinating to me and I do hope I am making sense in my post.> Likewise. Jean *********** K. Jean Cotterman RNC, IBCLC Dayton, Ohio USA *********************************************** To temporarily stop your subscription: set lactnet nomail To start it again: set lactnet mail (or digest) To unsubscribe: unsubscribe lactnet All commands go to [log in to unmask] The LACTNET mailing list is powered by L-Soft's renowned LISTSERV(R) list management software together with L-Soft's LSMTP(TM) mailer for lightning fast mail delivery. For more information, go to: http://www.lsoft.com/LISTSERV-powered.html