- [Voiceover] Lactation is a process
where milk is made and ejected
from the mammary glands inside the female breasts.
Besides being really nourishing for a suckling baby,
breast milk can also boost a newborn's immune system
because it contains antibodies
that the baby can't yet make on its own.
But overall, breast milk supplies all of the nutrients
that a growing infant needs
for the first six months of life.
So before we look at the mechanism of lacation,
let's just get oriented to the anatomy of the female breast.
So this is a woman's left side here.
And here is her left arm raised up in the air.
And this here is her pectoralis major muscle.
And the pectoralis major
is the primary muscle of the chest.
And the reason I mention the pectoralis major,
or the pec major, is just because the breasts
on the left and right side overlie the pec major
on the left and right side.
So it's just to give you a clearer idea
of where exactly the breasts lie
in relation to the chest wall.
And so what I've done here is I've cut away
the overlying skin on part of the breast
so we can look at deep structures
on the right side of the breast
and we can look at superficial structures
on the left side of the breast.
And remember, I mean right side and left side
from the perspective of our lady here.
So the breast in both females and males
contains special glands called mammary glands.
And mammary glands are actually modified sweat glands
that are able to produce and eject milk.
So in women they develop around the time of puberty
and in men they actually don't get developed.
They stay pretty benign.
And actually, before pregnancy,
the mammary glands don't really make up
a huge percentage of a woman's breast.
But during pregnancy they sort of expand
and branch out in a big way in response to stimulation
by hormones such as estrogen and prolactin.
And so they're actually a little bit tough
to see on this drawing here.
So I'll just blow them up for you a little bit.
So we can get a better look at the anatomy
of a mammary gland.
So these mammary glands,
surrounding them, almost like a net encasing them,
there are these cells called myoepithelial cells.
And the myoepithelial cells are special cells
in that not only are they lining the outside
of the mammary glands,
but they also can contract and squeeze down
on these glands to squeeze milk out of them.
So milk is drained toward the nipple
through ducts called lactiferous ducts.
And from there the milk can be ejected out
through the nipple, through these tiny holes
all over the nipple called nipple pores.
And so let's take a look at what this would look like
on the bigger drawing here.
So we've got our myoepithelial cells
lining the outside of these mammary glands.
And then they'll squeeze milk out of the mammary glands.
Send the milk along the lactiferous ducts,
toward the nipple,
and remember this is happening in all of the mammary glands,
and then it's ejected out of the nipple through
tiny holes in the nipple called nipple pores.
And actually, let me label this
as a lactiferous duct here.
And while we're in this nipple area,
you might notice that that there are these
dark, circular areas around the nipples.
They're called areolae.
And the areolae serve a couple of different functions.
The first one is that they contain these little bumps
called the areolar glands, or Montgomery glands,
that's the other name for them,
and the areolar glands secrete
a bit of an oily substance called lipoid fluid.
And the lipoid fluid moisturizes the nipple
so it doesn't get dry or cracked during breastfeeding.
The second function is more for the baby's good.
It turns out that the darkened areolae
sort of give the infant a target,
something to aim for.
They actually don't have the best vision
when they're born, so this helps them
to find their food source a little bit easier and quicker.
And actually I forgot to mention,
there's some research that suggests
that the lipoid fluid made by the areolar glands,
that it has a certain smell that attracts the baby as well.
So the areolae serve a couple different functions.
The breast also has a fair amount of fatty tissue,
or adipose tissue,
making up most of its content.
The fat actually also supports
all of the glandular structures we've mentioned.
So with all of this stuff going on in the breast,
the glands and all of the fat,
it can get a little heavy,
especially when the mammary glands are
full of milk during lactation.
So it needs these special suspensory ligaments,
also called Cooper's ligaments,
that help it remain anchored to the chest wall.
And that's what you see here in green.
So now that we've looked at the major anatomy of the breast,
let's get to what happens in lactation.
Lactation begins when an infant
begins to suckle on mom's breast.
But let's take a closer look,
because there's some pretty cool
neural pathways that are involved.
So when a baby starts to suckle,
special receptors called mechanoreceptors in the nipple,
they get activated and they start to send messages
up the spinal cord and into mom's brain,
to the hypothalamus.
And at this point, the hypothalamus,
when it receives these messages,
it does two really cool things.
It sends on signals to a set of oxytocin neurons
in the posterior pituitary gland,
telling them to make oxytocin.
And so here you can see oxytocin being produced.
And the hypothalamus also sends an off signal
to a special type of neuron in the anterior pituitary
that releases a hormone called
prolactin inhibiting hormone.
And these neurons in the anterior pituitary
are called PIH neurons.
And they have a bit of a funny job.
So, as their name might suggest,
they inhibit other neurons in the anterior pituitary
from producing prolactin.
So since they hypothalamus has turned them off,
now the prolactin neurons in the anterior pituitary
are free to make prolactin to their heart's content.
And you can see them producing prolactin here.
But why is this important?
Well, it's important because prolactin causes
the mammary glands to start producing milk.
And oxytocin stimulates these myoepithelial cells
that surround the mammary glands,
oxytocin stimulates them to eject the milk
out of the nipple so the baby can be fed.
So you kinda need both of them to have proper breastfeeding.
And interestingly, I said at the beginning that
it is the suckling of the baby
that sorta kicks off this whole neuronal cascade
to cause the let down of milk,
but remarkably,
even the sound of a baby's cry
and it doesn't have to be mom's own baby,
it can be the baby of a complete stranger,
but when mom hears the sound of a baby's cry
her hearing centers in her brain
will actually trigger this cascade from here.
And will cause milk creation and ejection.
And this mechanism sorta evolved as a safegaurd
for our babies.
To ensure that crying babies could still be fed
by other lactating women,
even if their own mother wasn't around,
so that they could still grow and stay healthy.