00:00
Let's look at how ducts are named in glands.
Well, they can be named in a number of different
ways. Firstly, you can name them according
to the location you see these ducts. I mentioned
a large compound gland earlier and that large
compound gland is divided by connective tissue
into large lobes and then smaller lobules.
Well, histologically you have done often sections
through ducts that are in, between different
lobes, interlobular ducts. You only really
see these small ducts. And those small ducts
when they are located between a lobule is
called an interlobular duct and within the
lobule, it is called an intralobular duct.
00:57
You need to be able to identify these different
ducts when you see sections through some of
the glands. Often they are classified according
to, not just say structure, but also their function.
01:11
They are called excretory duct if their job
is only to convey the secretory product and
most of the large ducts, the interlobular
ducts are excretory ducts because they have
no other function than carrying the secretional
product to the location where the secretory
product is going to be active. But a lot of
secretory ducts are involved with changing
the compounds, the components of the secretory
products. They change the compounds, the components
because they are involved with transport of
material into the lumen and the absorption of
material from the lumen. So they will have
a secretory function just as much as the secretory
cells do, absorption of material or secretion
of material. And in this case, you will see
in glands often ducts we termed striated ducts
or intercalated ducts particularly in serous
secreting or protein secreting glands. Remember
these striated ducts and intercalated ducts
are really involved with modifying the secretion
product. Sometimes we name ducts according
to where they are located. For instance, the
ductus deferens in the male reproductive system
sometimes they are named after the individuals
who first described them. Well let's have a look
at a couple of images illustrating certain
ducts. Here is an interlobular duct.
02:57
Notice the secretory acini or the secretory units
on the right hand frame of the slide, secretory
units are serous because they are rather dark
staining, pink staining. There are the granules
inside the cells of the apex of the cell,
the protein granules. But look at the duct,
it is seperated from the secretory units by
a fair of connective tissue, so that indicates
that connective tissue is dividing the gland
into different lobules. Down below that structure
that has a reddish color in the middle happens
to be a blood vessel. Normally, as I said
earlier, blood vessels and ducts accompany
these connective tissue septa seperating lobules
from each other. Now have a look at this section.
It is taken through a serous secreting gland.
04:00
What dominates are the white circular spaces
you see. They happen to be fat cells or adipocytes,
and similar to other mucous secreting
cells I explained earlier, the content of
these cells is lost during processing. Have
a look at the left hand side of this picture
and see if you can make out intralobular ducts.
They have a circular shaped lumen, and if
cut nice transversely, then they have a nice cuboidal
epithelium. This is a high magnification again
through a protein secreting gland showing
striated ducts. Again, look at the tube on
the left hand side of the image. It is a striated
duct, but have a look at the luminal area
and then move your eyes and look at the basal
area of this epithelium, and notice that there
are these little pinkish or reddish stripes
running along the basal aspect of this epithelium.
05:16
That is why they are called striated ducts.
And those striations represent firstly the
arrangement of mitochondria in columns along
the basal portion of the cell and these mitochondria
are arranged wiithin many many basal folds
of the epithelial cell. And these mitochondria
are there to provide the energy for active
transport because striated ducts are very
important in protein secreting glands because
they modify the secretory product.
05:53
So these mitochrondia provide the energy for active
transport, to move material from the lumen
into the underlying connective tissue. And
the basal folding is a way of increasing the
surface area to create more space for these
transport channels and also to house many
many more transport proteins. Now have a look
this slide very carefully. It again is a serous
or a protein secreting gland. Pickout the secretory
units or secretory acini and acinous is a
grape, berry like structure. It is a cluster
of cells. Let's see if you can find an intercalated
duct. They are very hard to see. They are very,
very very small in dimension and very short
and really only obvious in protein secreting
glands, not mucous secreting glands because
in mucous secreting glands, the secretion
product is not modified. But in protein secreting
glands as I have indicated earlier, it is
modified. So these ducts are also quite prominent
when you see sections of protein secretory
glands. Well have you found that? There it is.
07:22
A little tiny white spacious lumen and
if you look very carefully you see a cluster
of cuboidal type epithelial cells surrounding
or making that lumen. That is an intercalated
duct. Well, ducts have many functions, which I have
explained as we have gone through this lecture.
07:50
One is just to convey secretions and we call it
an excretory duct. Sometimes the duct needs
to modify the secretion product of the gland
and we will see examples of that when we look
at sweat glands in another lecture on skin
and also when we look at the salivary glands.
08:10
Sometimes ducts store secretion. When we look
at the prostate gland in the male reproductive
system and also the mammary gland, we will
learn that when the secretion product is produced
by the cell, it is often stored in the duct
system until it is used or wanted.