The Neonatal Period: Lactation and Nursing

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  • 0:07 Mammary Glands
  • 1:43 Prolactin and Oxytocin
  • 4:44 Colostrum and Breast Milk
  • 6:15 Weaning
  • 7:23 Lesson Summary
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Lesson Transcript
Instructor: Heather Adewale

Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.

Ever wonder how the mother's body knows when to produce milk for her coming baby? Learn about the hormones and cells involved in milk production and release in this lesson on lactation and nursing.

Mammary Glands

So, your brand new baby has just been born! How exciting! Now what? Well, one of the first things a new mother has to do is learn to breast feed.

Just as the baby has to prepare to enter the outside world and adapt to its new environment, the mother's body has to prepare to take care of her newborn. Around the sixth month of pregnancy, the mother's body prepares to produce milk for the coming newborn.

First, the mammary glands in the mother's breasts enlarge and have fully developed by month six. These glands are like enlarged and slightly modified sweat glands. They contain cells that produce colostrum and milk under the influence of the hormone prolactin. Because these glands secrete their product, that's milk, outside the body, they are called exocrine glands.

Okay, I know that's a lot of keywords in one definition, but don't worry, we'll come back to them. But first, let's continue with how the mammary glands work.

Myoepithelial cells in mammary glands aid in milk let-down.
Myoepithelial Cells Diagram

Once milk has been produced, it needs to travel from the mammary glands to the nipple, right? Well, this is under the influence of another hormone, called oxytocin, as well as the presence of myoepithelial cells, which surround the mammary glands. Myoepithelium are similar to muscle cells. They contract and push the milk out of the mammary glands and down ducts towards the nipple. This process is known as milk let-down.

Prolactin and Oxytocin

Okay, now that we know what happens, let's get back to some of those keywords. First up, the hormones! Ahhhh hormones, they seem to be involved in everything, don't they? In this case, we have two different hormones, both of which originate from the pituitary gland in the brain and travel to the mammary glands through the bloodstream.

Diagram of the anterior pituitary gland
Anterior Pituitary Diagram

Prolactin comes from the front part of the pituitary, which is called the anterior pituitary. Prolactin (PRL) is a protein hormone whose major target cell is the mammary glands. Secretion of prolactin increases during pregnancy and nursing. It stimulates mammary gland development and enlargement, as well as milk production.

Diagram of the posterior pituitary gland
Posterior Pituitary Diagram

Now, just being able to produce milk isn't enough. The mother's body has to get that milk from the mammary glands to the nursing baby. That is where our other hormone, oxytocin, comes in. Oxytocin is released from the back part of the pituitary, which is called the posterior pituitary.

Secretion of oxytocin (OT) increases towards the end of pregnancy when it stimulates uterine contractions during labor, and after pregnancy when it stimulates milk let-down from the mammary glands to the nipple.

So, your next question may be how does the mother know when to release milk? This is where our newborn baby comes in. When the baby cries, the mother's brain recognizes the sound and it triggers the release of both prolactin and oxytocin. These hormones work together to trigger lactation, or the production and secretion of milk from the mammary glands. Let's look at the steps involved:

  1. Crying of the baby, as well as thoughts of your baby or even the crying of another baby, can stimulate the hypothalamus, which in turn stimulates the release of prolactin and oxytocin from the pituitary.
  2. When the baby starts to suckle at the nipple, a physical stimulus is sent to the mother's brain, which causes more oxytocin and prolactin to be released.
  3. Prolactin and oxytocin travel to the mammary glands, where prolactin stimulates the production of milk in the glands and oxytocin stimulates the myoepithelial cells to push milk from the glands, down the ducts and toward the nipples.
  4. Milk gathers at the nipple and is released into the baby's mouth. And then, hopefully the crying has stopped. At least for now anyway!

Milk production and secretion occurs in a positive feedback loop.
Nursing Positive Feedback Loop

This is called a positive feedback loop because as long as the baby keeps suckling, milk release will continue. To stop the positive feedback loop, the physical stimulus of suckling needs to be removed.

Colostrum and Breast Milk

Okay, so now that you know all about how a mother produces breast milk, let's look at breast milk itself. Remember back to that definition of the mammary glands? That one with all the keywords in it? See that one there? Colostrum.

Well, did you know that there are different kinds of breast milk? And that colostrum is one of them? Colostrum is a secretion that is thicker and contains higher levels of protein and less fat than normal breast milk. It is produced during the first few days after birth and contains high levels of antibodies to help newborns ward off infections until their immune system becomes fully functional.

It also helps prepare the newborn's digestive tract by sealing the permeable spaces in the intestines and initiates the removal of the waste product meconium, or the first stools, from the intestinal tract.

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