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Anatomy of the Breast

By February 10, 2022Uncategorized

While becoming an IBCLC I was truly baffled at how little I actually knew about my own body and breast. As a teenage girl and college student the most I knew about my breasts was that they were small and someday they might be able to breastfeed my babies. I had no clue about structures, anatomical features and that size had NOTHING to do with function and capability of breastfeeding. 

I think many women and moms fall into this category. We have breasts but actually have very little understanding of what is going on in our chest. We are taught very little about what structures are actually responsible for making milk and what is needed to make breastfeeding possible. Knowing how your body works can be so empowering. It can give you peace of mind that your body is capable and made for a successful breastfeeding journey and it can help you to know when you might need to seek out some help from an IBCLC. 

Let’s take a closer look at breast anatomy and physiology and what is happening on both the outside and inside of the breast

External Structures (the outside of the breast)

Let’s start at the surface and define a few structures on the outside of the breast. 

First and foremost you have the areola and nipple. The nipple is the small portion that often sticks out or everts at rest or when stimulated due to bundles of smooth muscles. Some moms may have what is referred to as an inverted nipple. This means their nipple never sticks outward but rather stays dimpled or pulled in towards their chest wall or rib cage. Other nipples may just be flatter but stick out with stimulation or pumping. The average width of the nipple when everted (or sticking out) is about ½  an inch wide and the average length is about ¼ inch (breastfeeding and human lactation 4th edition).  At the end of the nipple are openings often referred to as nipple pores. The nipple pores are where milk comes out or is ejected from the breast by the smooth muscles. On average, there are about 10-20 pores that milk can drip or spray out of when feeding/pumping.

Moving outward from the nipple is the areola.  For most mothers, this area is a darker color than their skin color. On the areola are small bumps called Montgomery glands. They can be raised and sometimes look like pimples or be flat and not very noticeable. These are milk making glands combined with oil glands. On average, areolas have 8-10 Montgomery glands per breast. These glands are thought to be scent guiding for the baby and help the baby to find the breast and latch. Additionally, from an evolutionary standpoint, these glands might help with nipple stimulation and increase colostrum intake to ensure milk production and survival of the baby. 

Many interesting changes occur to the outer appearance of your breast, areola, and nipple while pregnant and breastfeeding.  During the third trimester, many moms will see nipple/areola darkening as well as an increase in size all together. This is thought to help with contrast to help the baby to easily identify the nipple while latching.

Many mothers are surprised to see they have hair follicles surrounding their nipples. This is normal and most women have some hair on the outer edge of their nipple/areola. Remember that your breast, nipple and areola are part of your skin so hair follicles, color variation, stretch marks, freckles and moles are all normal. The outside appearance of breasts can have so many variations of normal, so your breasts may look different than your mom’s, sister’s and friend’s, and that is okay! 

Now that we have looked at the outside of the breast, let’s take a look at what is on the inside.

Internal Structures (inside of the breast)

Under the surface of the breast is the milk-making framework. It’s such an incredible system!

The major building blocks are the alveoli. The alveoli are where milk is created and stored and they are arranged in clusters and surrounded by muscle cells.  The clusters are called lobes or lobules and they drain into the lactiferous ducts, which look similar to a broccoli stem. Some of the ducts connect to each other and others end as nipple pores where the milk comes out. 

Milk sprays or drips out of the nipple pores when the nipple is stimulated by the baby or the pump. This is called the Milk Ejection Reflex, or the letdown reflex.  When the baby begins suckling or when you start pumping, oxytocin is released by the posterior pituitary gland in the brain. This release of oxytocin causes the muscle cells that surround the alveoli to squeeze. This squeeze pushes the milk into the ducts and down towards the nipple opening. This process happens approximately every 5-7 minutes while you are nursing or pumping. This timing means the alveoli aren’t releasing all the milk at the exact same time but in bursts- more like a pattern. This is why, typically, most women will have multiple letdowns or flows of milk while breastfeeding their babies. 

The cool thing is that when oxytocin is released, it also widens and shortens the ducts. This change of pressure in the breast is what helps your breast drain effectively. And probably the most phenomenal thing about oxytocin is it can be activated by many things and not just the tactile stimulation of a baby suckling at the breast. Thinking of your baby, being in close contact with those you love, hearing a baby cry, or even sex with your partner can cause an oxytocin release and milk to FLOW. (This is surprising and shocking to so many to have milk spray or flow during sex BUT it can totally happen and is normal!) 

It is also imperative to chat about the things in our breast that don’t directly make milk but also serve a purpose. Another structure that all breasts have is a framework of ligaments called Cooper’s Ligaments and they attach your milk-making tissue and fat tissue to your chest wall. These ligaments determine the “perkiness” of your breasts. It’s also important to note that ligaments during pregnancy are exposed to a hormone called relaxin, which has an affect on all ligaments in the body. THis means that your breast “perkiness” will change after pregnancy whether you breastfed or bottle feed, largely due to the physical changes to the Cooper’s ligaments! To be honest as a first- (and even second!) time mom, I was relieved to learn that I wasn’t ruining my body by breastfeeding, but that changes were inevitable either way. Breasts tend to double in size during pregnancy, so if you think that the change in size and the changes to the ligaments aren’t going to have lasting effects… that is wishful thinking!! 

In any case, as Jan Riordan puts it perfectly “No other human organ displays such dramatic changes in size, shape and function as does the breast”. It’s incredible the intricate function and design our bodies are capable of!

Check out these two incredible visuals of everything we chatted about above: 

Breast Anatomy & Lactation

Once you understand breast anatomy and physiology, it is easier to trust that when your baby latches, your body has milk and it flows to your baby. Of course there are so many variations of normal as with any anatomy of the human body. Prenatal consults with our IBCLCS are a great way to get an evaluation of your breasts and address any individual concerns you may have when it comes to breastfeeding with your breasts. If you have any other questions or concerns about your breast anatomy, directing them to your provider would be the next step after meeting with one of our IBCLCs. Lastly, remember that no matter your breast anatomy, babies have reflexes to help them latch and often no matter the small differences or variations, babies can still breastfeed successfully!

Thanks for stopping by,

Aubri Lutz







Breastfeeding and Human Lactation 4th edition

The Nursing Mothers Companion 20th edition

New Mother’s Guide to Breastfeeding- American Academy of Pediatrics 2nd edition