Katherine writes:
<<<some mothers then also > have years of inadequate hormonal stimulation
from menstrual > irregularities>>
so you're saying that hormonal stimulation from menstruation is a factor
in fully developed lobes, lobules and alveoli?
are you saying it's necessary?>
Judith writes: <If I'm reading Lawrence and others correctly, rapid
development of ducts and lobes, etc is at puberty. Thereafter normal
cycling contributes to a small and very gradual development of alveolar
buds. Complete development does not take place in the absence of
pregnancy, where growth of ducts, lobes and alveoli are all rapid.  . .
.An everything I've read suggests that the "normal" state of the human
adult female is pregnant or breastfeeding, with only a few cycles between
breastfeeding and the next pregnancy. >
Actually, I hate to keep using the word 'fascinating' but this article I
put into my post on "Effect of obesity, and physical fat pressing on
alveoli" on July 28 truly is:
<Russo J, lRusso IH Development of the Human Mammary Gland in: The
Mammary Gland, Development, Regulation, and Function ed. by Neville MC,
Daniels CW 1987 Plenum Press, NY. pp 67-93. Interesting pie chart of
differing amounts of different types of tissue depending on age/parity
(p. 89).>

It gives detailed diagrams about the early stages of development of the
TDLU-the terminal ductal lobular unit as well, and explains fully how the
menstrual cycles contribute. It's correct that if no pregnancy ever
occurs, they do not develop to their final stage of fully secretory
alveoli. But each menstrual cycle contributes something to lobular-ductal
development.

But if there have been few menses, the hormones of a pregnancy take right
over and finish the development. They involute a lot if there is time
between pregnancies, and each placenta partially redevelops them anew
again, so spending most of one's reproductive life either pregnant or
breastfeeding and not many menses still works just fine.

However, if I understand Lisa Marasco's work, years of menstrual
irregularities from PCOS, if severe enough, may hamper regular monthly
development till pregnancy, often after medically overcoming infertility
problems, can finally take over the job. I also seem to remember reading,
perhaps in some past JHL, about supplemental hormones given between
pregnancies, helping someone develop more lobular tissue to succeed in a
subsequent pregnancy when she had had insufficient  glandular tissue with
a first pregnancy. There are other factors in the connective tissue that
have an effect too.

<Knight CH, Peaker M, Development of the mammary gland, J Reprod Fert
(1982), 65, 521-536. "Mesenchyme forms blood vessels, lymphatics,
connective tissue, including fat pads, without which mammary epithelium
cannot proliferate or differentiate, and which provides the necessary
space, support and local control for duct elongation and ultimately,
lobulo-alveolar proliferation. During juvenile life an ordered extension
of ducts takes place within the fat pads. There "is an inhibitory zone
around each duct into which other ducts cannot penetrate and in normal
circumstances, development does not proceed beyond the duct end-bud
stage." (at the juvenile stage) In some species, proliferation of mammary
growth continues on into lactation for 5 days. (mouse, rat) In guinea
pig, little change in pregnancy, but 2 days after parturition, there is a
large increase. "A period of involution is an essential pre-requisite for
successful redevelopment and subsequent lactation." (at least in animals)
Adjacent ducts (in mice) never approach closer than o.25 mm. to each
other, thus allowing space for subsequent development of alveoli. . .
chemical of some sort which diffuses into the adjacent fat pad and
prevents other ducts from penetrating into that area . . ."(p. 531)

Somewhere along the line, someday, someone out there needs to tie in and
familiarize us with the Tanner stages and suggest how we might correlate
those with our assessments of the developmental stage of a mother in whom
we we suspect insufficient glandular tissue.

Lactnet appeals to me far more than solitaire to avoid tackling
housework;-)

Jean
************
K. Jean Cotterman RNC, IBCLC
Dayton, Ohio USA

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