Milk production

This page discusses some aspects of milk production that are relevant to the breastfeeding mother. It is not meant to be a complete discussion of the details of milk production.
    First, a few remarks about the anatomy of the breast:

• Most of the breast is made up of fat and connective tissue.
• Embedded in this, there are little sacs surrounded by milk-producing cells.
• These little sacks come in clusters, each cluster opening into a milk duct. There are about fifteen to twenty such ducts in each breast.
• These milk ducts connect to openings in each nipple.

Milk production and ejection:

• The milk producing glands develop during pregnancy.
• Lactation is suppressed during pregnancy by progesterone, produced mostly by the placenta.
• After birth, the placenta is delivered. Progesterone production drops drastically, and lactation starts.
• Milk produced in cells collects in the little sacs.
• Some of this milk flows down the ducts and collects in reservoirs ("sinuses") underneath the areola. This is foremilk, which is watery and low in fat and calories.
• When your baby nurses, the action of the jaws and tongue drains the milk from the sinuses.
• At the same time, nipple stimulation causes your body to release two hormones, oxytocin and prolactin.
• Oxytocin causes the milk sacs to contract (it also causes some other muscles in your body to contract). This pushes the milk collected in the sacks to the sinuses (letdown). This is hindmilk, rich in fat and calories.
• Prolactin causes the breasts to make more milk.
• This extra milk also collects in the sacs, and may also be let down if your baby is continuing nursing. Letdown can occur several times during the course of a breastfeed.
• Milk left in the breast puts pressure on the milk-producing cells. This pressure causes them to stop producing milk.
• Thus, the more your breasts are emptied, the more milk they make. If they are not emptied, they stop making milk.

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