Making Milk | Lactation Hormones

Now that you've gotten the fundamentals of the lactating breast anatomy, we're going to introduce you to the hormones involved in breastfeeding also known as the physiology of lactation. For your body to make milk you need the gear (breasts) but you also need the electrical wiring and communication to get the system working. Let's jump in. 

The Key Players (1, 2):

  • Prolactin - Causes the body to MAKE milk
  • Oxytocin - Causes the body to RELEASE milk 
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In the last post on anatomy, we mentioned that your breast has nerves that branch out all over including in the nipple and when your baby nurses at the breast, receptors in the nipple are stimulated signals are sent to your brain. This is pretty neat because your breast and brain are talking in real-time and changes are happening lightning fast. These signals go straight up to a part in your brain called the hypothalamus and the hypothalamus is in charge of your endocrine (hormone production) and nervous system (2). The hypothalamus has several roles but in lactation this is the guy who decides what hormones get released and can start or stop hormone production throughout the body based on the signals it receives. When your baby is suckling at the breast, your brain (specifically the hypothalamus) gets the signal "Baby is hungry and needs food, it is time to make milk" and the hypothalamus amps up oxytocin production and turns off the production of PIH (prolactin inhibiting hormone) (1, 2). Wait, so why does it turn one on and the other off? Right! We need to shut off the production of the prolactin inhibiting hormone because we need prolactin to tell the mammary glands to make the milk! So now we have our body being pumped full of prolactin which is making the milk with our blood and we have oxytocin activating those little cells around the mammary glands (remember myoepithelial cells surrounding the alveoli) to squeeze the glands and get the milk out of our bodies and into our baby.

Did You Know?

The sound of a crying baby (any baby!) can also trigger this hormonal response (1)! This is our biological instincts kicking in to protect new life because breastfeeding is not just food but a huge source of comfort to a baby. A baby's crying sends a message straight to the hypothalamus and amps up the lactating hormones and typically, this results in an ejection of milk and a wet shirt. Note to moms: breastfeeding pads are a lifesaver or at least, a shirt saver. 

Yes, pumping stimulates the breast similarly (but not quite the same effectiveness) to a baby's suckle. We will discuss in detail how a pump works in a different post but generally, pumps can replicate the suckling movements of a baby's mouth by quicker and lighter suctioning of the nipple. This fluttery kind of tugging from the breast pump sends those signals from the nipple to the hypothalamus and voila - milk production (2). 

Oxytocin, also known as the "love" hormone, plays a huge role in various aspects of mothering (2)! It is involved in sexual arousal, affection, parenting style, bonding - can you tell its super important? During labor and delivery, oxytocin is in charge of making your uterus contract and push baby out into the world. [This is why some women receive "Pitocin" which is synthetic oxytocin during labor to help labor progress in certain situations.] After baby is here, oxytocin is the hormone that encourages you to bond with your baby, to snuggle them close, to be loving and responsive, all of those motherly human behaviors come from this hormone (6-8). Mothers who breastfeed are found to have higher parental responsiveness and more empathy to infant's crying which is a predictor of secure attachment and how our children will form relationships as they get older (3, 4, 9). Oxytocin also helps us to stay calm and collected by lowering our stress response and this in turn affects how our children regulate our emotions and deal with stress later in life (5). Takeaway - we love oxytocin and evidently, it loves us back!  

References

(1) World Health Organization. (2009). The physiological basis of breastfeeding. Infant and Young Child Feeding: Model Chapter for Textbooks for Medical Students and Allied Health Professionals. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK148970/

(2) Lauwers, J. & Swisher, A. (2015). Counseling the Nursing Mother: A Lactation Consultants Guide. Burlington, MA: Jones & Bartlett Learning.

(3) Feldman, R., Gordon, I., Schneiderman, I., Weisman, O., & Zagoory-Sharon, O. (2010). Natural variations in maternal and paternal care are associated with systematic changes in oxytocin following parent- infant contact. Psychoneuroendocrinology, 35, 1133–1141.

(4) Pearson, R., Lightman, S., & Evans, J. (2011). The impact of breastfeeding on mothers' attentional sensitivity towards infant distress. Infant Behavior & Development, 34, 200-205.

(5) Olff M, et al. (2013). The role of oxytocin in social bonding, stress regulation and mental health: an update on the moderating effects of context and interindividual differences. Psychoneuroendocrinology, 38( 9), 1883-1894.

(6)Felman et al. (2010). Natural variations in maternal and paternal care are associated with systematic changes in oxytocin following parent- infant contact. Psychoneuroendocrinology, 35, 1133–1141.

(7) Naber et al. (2010). Intranasal oxytocin increases fathers’ observed responsiveness during play with their children: a double- blind within-subject experiment. Psychoneuroendocrinology, 35, 1583–1586.

(8) Pearson et al. (2011). The impact of breastfeeding onmothers' attentional sensitivity towards infant distress. Infant Behavior & Development, 34, 200-205.

(9) De Wolff, M.S. & IJzendoorn, M.H. (1997). Sensitivity and attachment: a meta-analysis on parental antecedents of infant attachment. Child Development, 68, 571–591.