According to Natalie Angier's Women: An Intimate Geography, milk is actually a modified form of sweat and the mammary glands very similar to the sweat glands. Makes lactation seem a little less of a miracle, doesn't it?

Mechanism of lactation:

The mammary glands in mother's body have been affected by oestrogen and progesterone throughout pregnancy to develop and prepare for lactation. Prolactin levels rise at the end of pregnancy as oestrogen and progesterone levels fall and this induces true milk secretion.

It goes something like this:

1. baby is put to nipple.
2. baby sucks as this is one of the few instincts baby is born with.
3. suckling is detected by the dense concentration of nerves in the nipple and areola.
4. this causes secretion of oxytocin by the neurohypophysis. prolactin levels are also increased by suckling.
5. circulating oxytocin apparently causes myoepithelial cells in the mammary glands to contract causing let-down of milk.
6. when suckling stops, milk secretion ceases too.

Maintenance of lactation is dependent on various hormonal triggers and regular suckling at the breast. Although weaning of the baby at somewhere between 3 and 6 months of age has become common in Western society, mothers in more primitive societies have been known to nurse their children up to the age of 4 years. In extreme cases, lactation can be maintained for many years as long as there is demand suckling at the breast ...

lactation: the secretion of milk from the breasts; the period of suckling the young until weaning.

Dictionary of Sexology Project: Main Index

Lac*ta"tion (?), n.

A giving suck; the secretion and yielding of milk by the mammary gland.

 

© Webster 1913.