MILK EJECTION

ejection is critical for successful lactation, because
only small volumes of milk (1–10 mL) can be either
expressed
46
or removed by the breastfeeding infant
40
before milk ejection. Failure to remove sufficient quan-
tities of milk results in a decrease in milk production
because of local control mechanisms.
47
Stimulation of
the nipple initiates milk ejection via initiation of nervous
impulses to the hypothalamus, which stimulates the
posterior pituitary gland to release oxytocin into the
bloodstream.
48
Oxytocin causes the myoepithelial cells
surrounding the alveoli to contract, forcing milk into the
ducts. This results in increased intraductal pressure,
49
duct dilation
40,50
(measured by ultrasound), and conse-
quently increased milk flow rate
50
(measured by contin-
uous weigh balance during breast expression). Multiple
milk ejections almost always occur during breastfeed-
ing
40
(mean, 2.5; range, 0–9) and breast expression
50
(mean, 3–6 for 15-minute expression period), and alhough many women are able to sense the first milk
ejection, few are able to sense subsequent ones.
While it is well known that stress can influence milk
ejection—resulting in diminished amounts of milk re-
moved by both the infant
48
and breast pump
51
—it is
often the subtle stress which affects maternal confidence
and subsequently milk ejection that is overlooked. There-
fore, it is important to provide positive support to the
mother during both breastfeeding and pumping. Another
factor that may influence milk ejection and milk removal
is the ductal anatomy of the breast. In a study of mothers
expressing with an electric breast pump, ultrasound was
used to image duct dilation in the breast that was not
pumped. It was found that mothers with larger ducts
expressed more milk during milk ejection and had longer
milk ejections than mothers with smaller ducts.
50
There-
fore, the rate of milk removal for a mother may be
influenced in part by her ductal anatomy