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.
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