Alveoli are small sacs that are inside the mammary gland. These are where milk production occurs, as well as the storage of breast milk. The alveoli are group inside the mammary lobules. For the average woman, each breast contains 15-20 of these.
- Alveoli are produced during pregnancy to hold and produce milk.
- They are clustered together inside the mammary lobules.
- Milk is carried from the alveoli through the milk ducts to the areola, where those ducts are connected with larger ducts which then bring the milk to through the nipple.
Alveoli are the basic structural, functional and biological unit of the lactating breast. The alveoli are tiny sacs with extremely thin walls containing clusters of cells that secrete milk.
Oxytocin contracts the cells to squeeze milk into lacunae that drain into larger ducts that combine to form lobes of the breast. The alveoli are surrounded by a network of blood vessels and lymphatic tissue collectively called “the lactiferous sinus.” It is from here that the infant’s suckling draws fluid from the tissues surrounding the alveoli, which contains the milk.
The baby’s suckling also stimulates the mother’s hypothalamus to release oxytocin, which contracts the cells of the alveoli to squeeze milk into these sinusoids (ducts). The pressure of this contraction forces some of the milk out through the nipple during suckling.
The alveoli are in constant motion, with small clusters of cells moving toward the nipple and larger clusters moving away. These movements are responsible for the formation, at birth, of an extensive network of fine ducts which provide a large surface area through which milk can be transferred from the alveoli to the baby’s mouth.
Milk is secreted not only by each alveolus but also by “milk fat globules” that form within the alveoli. These milk fat globules move constantly and coalesce to form larger pools of milk.