Prepubertal Stage - 1

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Из курса от партнера University of Illinois at Urbana-Champaign

Lactation Biology

4 оценки

University of Illinois at Urbana-Champaign

Lactation Biology

4 оценки

Lactation and especially milk, which is the product of that unique mammalian process, are routinely encountered within our daily lives. Nevertheless, they often are poorly understood by many, even including many who are engaged in the business of producing milk. The overall course goal is to introduce fundamental concepts that form the basis for understanding the biology of lactation, the biology of the mammary gland, and the products of that important physiological process. As a learner in this course, you will be provided with a series of easily understood presentations that collectively will help you build a foundation for greater understanding of lactation. You will be able to engage with other learners so that you can extend your learning beyond the video presentations. Ultimately, you will be able to construct your own mental model for understanding the wide range of topics that relate to the biology of lactation. Upon completion of the course, you will be prepared to expand your knowledge and understanding of lactation from other sources and experiences as you pursue your individual interests. Before you start the course, I suggest that you identify a question or several questions about lactation that you already have on your mind. This could be from your own experiences, something you read about or saw, or something you have wondered about. Write down your question(s) and use that to help you decide how to engage with the content of this course. You might engage with the modules in the order they are presented, or start with a module that is of particular interest to you, or pick and choose modules in any order. I encourage you to engage in all of the types of learning activities that this course has to offer, including but not limited to, the discussion forums, quizzes, peer-review assignments, and concept maps and other learning aids.

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Module 4: Mammary Gland Development

The tissue that we know of as the mammary gland (or udder or breast) may appear as relatively uncomplicated compared with some internal organs such as the heart or brain. The gland is outside the body wall, has a nipple or teat in most species, and has a series of ducts by which milk that is produced in microscopic blind tubes can be expressed from the gland. How can such a gland develop and what regulates that development? It turns out that the initial stage of development occurs extremely early in the fetal development of the animal. It then proceeds through a series of developmental phases, many of which are closely linked with the reproductive functioning of the animal, and eventually leading to the time when the gland is producing milk. Furthermore, the mammary gland is one of a few tissues that undergoes repeated cycles of development, functioning, regression, and redevelopment, again associated with the reproductive cycles of the animal. This module describes the various stages of mammary development and provides the framework for understanding how these stages relate to each other, as well as to the functionality of the gland.

Prepubertal Stage - 17:14

Prepubertal Stage - 23:43

Postpubertal Stage7:18

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Dr. Walter Hurley, PhD
Professor Emeritus
Department of Animal Sciences

[SOUND] >> Welcome back, in this video,

we're going to continue our exploration

of the different stages of mammary gland development.

Last video we talked a little bit about fetal development and

how the mammary gland develops in the fetus prior to birth.

In this one we're going to start talking about prepubertal development.

So again, remember the different stages of mammary gland development.

And here we're going to focus, in this particular case, on prepubertal

development of the mammary gland, from the time the animal is born, until

the time that she enters reproductive cycling at approximately puberty.

This is a mammary gland, a cross sectional mammary gland,

a section of a mammary gland from a ewe lamb about nine weeks old.

So let me give you some perspective on that.

In this particular species,

they're going to go through puberty at approximately six to eight months,

depending upon which time of the year they are born, which breed they are.

But clearly, at nine weeks, she's a long ways from having gone through puberty.

So this really gives you a really good idea of just how much development's

occurred or how little development has occurred, and

what we're going to talk about, the parenchymal tissue.

This area up here is called the fat pad, we talked a lot about that in the last

video with field development, and we'll continue talking about the fat pad.

Again, it's basically lard, it's solid adipose tissue.

You're going to see in a little bit, that it's a specialized tissue though,

it's not just like any other fat, and we'll get to that here in a moment.

This is a landmark, back here in the back corner.

This dark area, dark spot here is the supra mammary lymph node,

supra meaning it's above the mammary gland, supra mammary lymph node.

The glands of this particular species are in the inguinal region, so this is really

at the back end of the mammary gland, and it's kind of a nice landmark.

This area in here, this area called parenchymal tissue,

this is the epithelial tissue.

These are the branching ducts that are branching up and growing up into the fat

pad, elongating and branching and growing up into the fat pad.

And that's pretty much how that tissue is growing at this point.

So those would be the epithelial components.

And then sometimes it's called parenchyma,

sometimes the fat pad is actually called extraparenchymal tissue.

And depending upon who you're reading and who you're listening to.

So let's take another look at this,

this will be a coronal section through the gland.

So we're looking at a section through both glands, again,

remember that the sheep has two glands.

So again, we have the parenchymal tissue here, parenchymal tissue in the other

gland, and then the fat pad going throughout the two halves.

So this would be the line between the left and right half of the mammary gland.

Okay, let's take another perspective on this.

So that was kind of a cross-section, or thin sections through the tissue.

But let's take another perspective on this.

This is a wax cast of a heifer,

a dairy heifer mammary gland, very early on.

And what they would do then would be to sacrifice the calf, or

sacrifice the heifer, take the mammary gland off, infuse or

inject up through the streak canal in the base of the teat, molten beeswax.

And let it solidify, and then digest away all the soft tissues,

and this is the cast you get.

So you have the teat cistern down here, you have the gland cistern, or

what would be the gland cistern here.

And you can see, there's a few of the major ducts that are emanating from this,

or growing up into the fat pad.

Again, this fat pad would be all the area up above this thing.

To give you another perspective on this, what we've done is I've taken a dairy

heifer, we've interposed that wax cast I just showed you a moment ago, just to

kind of give you a rough idea of the size of the frame that we're talking about.

Not a lot of development at this point.

You can, on the other hand,

just see a little bit of kind of bulging area here that would be primarily fat pad.

And at this stage of development,

that's most of what the mammary gland is at this point.

Let's shift gears a little bit, so I've talked about bovine,

I've talked about the ewe, the lamb, let's talk about swine.

The top picture represents a cross section through the skin and the underlying

fascia, and then fat pad of the mammary gland, the nipples at the top here.

The parenchymal tissue we talked about would be this area right in here.

You can see it's a slightly different color than the rest of the fat pad,

the mammary fat pad, which would be this area in here.

And then the musculature underneath, lying underneath that.

The bottom picture, on the other hand, is taking something very similar to this, but

making a very, very thin section through it.

Fixing it, for histological purposes, staining it,

and then, again, taking a real thin section through that.

So the pink stained material is the proteinaceous material.

Again, it was stained with haematoxylin and eosin.

And then the white area down here would be the fat pad.

And several things to notice, you see there's pretty thick amount

of connective tissue right at the base of the teat.

You can actually see one of the lactiferous sinuses

here going down into the teat.

Remember, the mammary gland of the pig,

there are actually two glands that come out one nipple.

So each of those nipples has, actually, two glands in there.

And so, this would be one of them, and

the other one is just out of the plane of the section that we have here.

Several things to notice though, that there's this, again, these connective

tissue sheets that kind of emanate and run down through the fat pad.

This is another one here, another nice one going down here.

Also notice that a lot of these have a lumen in them.

And what we're going to find at this stage, but then later stages as well,

is that when those ducts continue growing into the fat pad,

they're actually following those connective tissue sheets and

then following those is kind of a tract.

So these things are going to continue developing, elongating down here, and

following the connective tissue sheets that are in this tissue.

The fat pad structure, it looks like it's kind of random, but it's actually a very,

very critical structure.

What I've done in the next slide is to give you an example of backfat, so

from the back of the pig.

The pink stained material at the top is the skin,

the stratified squamous epithelium, this is the backfat here.

And notice that the connective tissue, the pink stained material,

is nowhere near as highly organized as you find in the mammary fat pad.

And again, I just want to emphasize the idea that this is not just lard,

it's a specialized area because of the kind of connective tissue sheets that

are running through this thing.

Because again, they're going to be the tracts by which those major ducts

are going to enter and grow and elongate into the fat pad.

[SOUND]

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