Hi Jean,
First let me say that my understanding of all this is what I have
learnt from listening to many, many presentations by Peter Hartmann
over many years, and some of my thoughts and understanding may not be
100% accurate, but this is how I see it. I can't quote written
references, although I am sure there are specialised biochemistry
texts that could help.

>But while I can accept the concept that fat globules, if adjacent to a
>duct wall, may adhere somewhat stubbornly, there are other fat globules
>in the center of the stream just floating there, waiting to rise and
>separate themselves, molecule by molecule from the aqueous portion.

This is delving more into biochemistry than we usually need to, but I
would like to point out that fats in milk are not in the form of
separate 'molecules'. They are in globules (micelles?) of many
molecules of fat surrounded by cell membrane that originates from the
alveoli (milk-making) cell walls. (It is the presence of these
globules that gives creamy milk a more opaque appearance as they
scatter the light passing through.) These globules are 'pinched off'
from the cell walls as they are released into the milk. They then
tend to adhere to the membrane from which they came, so they appear
to be 'sticky'. They really only are released efficiently from the
membrane when squeezed out by the force of the MER, ie by the
myoepithelial cells contracting on the outside of the alveoli cells.

>I do not define the formation of foremilk nor its separation from the fat
>as "seepage" downward, or forward in the breast. I feel certain I read of
>the concept of lactose actively importing fluid osmotically inward
>through the duct walls to equalize the concentration inside and outside
>of those membranes, given time.

Actually I don't think this is 'given time'. The active movement of
lactose into the alveolus lumen by the alveoli cells surrounding that
lumen is what drives the volume, as water is drawn into the lumen
fairly quickly by simple osmosis. This is happening in the alveoli
luma (plural of lumen??). I don't think this happens in the ducts,
but I could be wrong.

Also, the ducts are far from being passive tubes for carrying milk
from the alveoli to the nipple. When the MER happens, they suddenly
expand dramatically in diameter, within a split second. Donna Ramsay,
here in Perth, Western Australia, has done ultrasound videos of this
happening and it's fascinating to see.

>
>My interpretation: this is both how the carbohydrate/protein component
>becomes more and more dilute, and how the volume of liquid increases,  in
>this additional process after actual secretion of the caloric and
>vitamin-mineral fractions from the alveoli. I think this is the basis of
>how nature supplies "the first  for thirst" and the occasional
>possibility of foremilk/hindmilk imbalance at some feeds.

My understanding is that lactose concentration in the milk is always
constant (as it actually determines the volume by it's osmotic
activity). I also think I have been told that the *total amount* of
fat secreted into into the milk per day is fairly constant. What
changes the *concentration* of the fat is the changing volume and the
MER (ie without MER most of the fat is left in the alveoli). So a
mother with oversupply will have lower *concentration* of fat
overall, but still the same *amount*. The baby can get this total
amount provided he is able to consume large volumes of this low-fat
milk. However, what may happen with oversupply is that the baby's gut
doesn't efficiently digest all that it takes and the milk travels
very quickly through from top to bottom. Hence the copious stool
output often seen, and symptoms of lactose malabsorption (wind in the
bowel, etc).

In all the cases of simple oversupply (ie simple foremilk/hindmilk
imbalance) that I have seen, the baby is putting on heaps of weight
(or at least adequate) - they are just miserable. In the few cases
that have weight loss, colicky symptoms and normal to oversupply,
there have been other complicating factors such as food intolerance,
which has compromised the baby's ability to efficiently absorb the
nutrients.

Re the discussion of amount of fat per feed being greater or less
when feeds are more frequent - I would say that there would actually
be less *per feed* (as the total amount is now divided over a larger
number of feeds) but at each feed, the first milk to come from the
breast, ie the 'foremilk,' is higher in fat *concentration* because
the breast is relatively emptier. So the milk appears to be creamier.
With frequent feeds, the baby takes a smaller volume per feed, and
therefore is likely to efficiently digest that feed, gaining the
benefits of all the fat available. If the baby was having smaller
numbers of larger volume feeds, then perhaps the gut is less
efficient, coping with such a huge load at one time.

>
>I agree that molecular activity is probably constant, sometimes more
>rapid than others, and the motion of the pectoral muscles probably plays
>a part.  But I believe there is enough relative quietude that the longer
>it is between feedings (and the longer the tubings, and/or the more well
>supported the breast), there can be a distinct opportunity for fat
>globules to separate and rise till they meet the obstacle of the duct
>wall or the already collected cream.

I admit I am with Gonneke, and can't think of it happening like this.
My understanding is basically the same as what Gonneke wrote.

> Won't others chime in with your
>$.02, please, no matter where you come down on the issues!
>What ho, you of OZ, where the research action is?

You asked!! ;-) Sorry it got a bit long-winded, but hope some of it
makes sense.
******************************************************************
Joy Anderson B.Sc. Dip.Ed. Grad.Dip.Med.Tech. IBCLC
Nursing Mothers' Association of Australia Breastfeeding Counsellor
Perth, Western Australia.   mailto:[log in to unmask]
******************************************************************

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