There’s no question that breastfeeding is good for babies. But what do you know about the science behind how boobs make milk?
During pregnancy, hormones prepare your breasts for breastfeeding. When your baby suckles, the prolactin hormone activates milk-making tissue.
This is a very common slang word, so it’s unlikely that anyone will get mad at you for calling someone a boob. But what is the etymology of this term?
The nipple
The nipple is the raised area in the center of the breast that contains milk duct openings for breastfeeding. It’s surrounded by a dark area of skin called the areola. The nipple and areola look different from person to person.
During pregnancy, the nipple grows in size and firmness to prepare for nursing after baby is born. The nipple also becomes tender and sensitive to the touch of a baby’s tongue. When a baby sucks, nerves on the nipple send a signal to the brain that causes the release of oxytocin. Oxytocin makes the muscles inside the breast contract, squeezing milk from milk-producing cells down milk ducts and out through the nipple.
Milk is a thick liquid that has many functions, from providing energy and building muscle to protecting the fetus during delivery. The hormones that make it start to kick in during the third trimester of pregnancy.
Breastfeeding requires a lot of muscle work from both the mother and baby. The more a baby sucks, the more milk is removed, and the more the body signals to produce more. That’s why it is important to feed often, especially during the first few weeks and months of life.
The lobes
Every breast contains a network of milk-producing glands called lobes. They are arranged in a pattern that looks like bunches of grapes and they connect to milk ducts that carry the breast’s milk to the nipple when you breastfeed.
Each lobe is made up of many smaller sacs called lobules. Each lobule is lined by cells that produce the milk you give your child. The lobules and ducts are found in a dark area of skin called the areola.
The lobes are made of glandular tissue* and fatty tissue**. The lobes are surrounded by other structures that help hold them together, including connective tissue and the pectoral muscle*. The lobules are also lined by cells that make the hormones that signal the body to make milk.
Each lobule has a cluster of alveoli (small, grape-like sacs that produce milk) that drain into a duct. Each lobe has 20 lobules and each lobule connects to a milk duct. These ducts drain into the areola, where they join to form a single nipple pore during breastfeeding.
During puberty, the glandular tissue in your breasts starts to develop into a more mature system of lobules and ducts. These changes are the earliest signs that you’re pregnant and they are part of what makes it possible to make milk from your breasts during breastfeeding.
The ducts
Since before you were born, your breasts have been preparing to make milk in a stage called lactogenesis. Hormones like estrogen and progesterone suppress the milk-making hormone prolactin until after your baby is born and the placenta is delivered, when they drop and prolactin takes over. The first milk made in this phase of lactogenesis is colostrum, which is full of antibodies and other nutrients your baby needs.
When your baby suckles, it stimulates nerves in the nipple and areola that tell the brain to release the hormones prolactin and oxytocin. These hormones cause the alveoli to begin making milk and muscle contractions that squeeze the milk from the alveoli into the ducts, which look like highways running through your breast. The milk is then transferred to the nipple and down the ducts to your baby.
The more you nurse or pump, the more your body produces milk. Your nipples may feel sore or full and you might notice that your milk seems thicker or more yellow as the production process continues, but breastfeeding is a supply-and-demand process. The more you remove milk from the nipples, the more your body makes to replace it. Your milk ducts branch off into smaller channels near your chest wall called ductules, which lead to a cluster of small grapelike sacs within your breast that make the milk, called glandular tissue.
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