I know I just introduced some new words, so let’s talk about milk making anatomy. Milk supply is anatomical just as much as it is hormonal or “supply and demand,” so this part is important too!

You likely already know that breast changes begin in early puberty. While those changes don’t kick off any type of location, they are foundational for what occurs during pregnancy and lactation, which is when mammary glands reach maturity.

Mature or sufficient breast tissue is made up of 15-20 lobes. These lobes, which are connected to the milk ducts, have clusters of alveoli within them, which are made up of alveolar cells. A single alveolar cell is called an alveolus. An alveolus has oxytocin receptor sites, prolactin receptor sites, milk secreting cells, and a lumen. The lumen empties into the milk ducts, where milk then moves down and out the nipple pores. 

During pregnancy, hormones like progesterone and estrogen that are released by the placenta cause the ducts and alveoli to grow and cause the cells to form prolactin receptor sites. Those sites, called lactocytes, are the ones that are filled by progesterone during pregnancy, but that soon empty out after placental birth so that prolactin can land and begin stage 2 of milk production.

We’ll talk about milk supply (both low supply and oversupply more later), but if you ever hear terms related to insufficient mammary tissue, what that is essentially referring to is all of this. There are some instances where these anatomical changes don’t happen fully or sufficiently, and that can then lead to supply concerns.