Digestive System 6- Small intestine

Digestive System 6- Small intestine


– I’ve got my pen.
Now, we were in the stomach. We passed
through the pyloric sphincter, and we are now
in the small intestine. And there are
actually three parts to the small intestine,
and so I feel like it’s we should probably
define those parts right away, so the first part
of the small intestine that we enter
is called the duodenum, duodenum. The duodenum is pretty short,
it’s about 10 inches long. And it forms like
kind of a C-shape directly out of the stomach. The duodenum feeds directly
into the next piece, which is called the jejunum, jejunum, so check it out. Hey, look, they even
labeled it here. stomach enters into the
duodenum, and then the duodenum, dude they done
forgot something, really, that’s just messed up,
because you forgot the jejunum. What do you think the next piece
of small intestine is called? The ileum, I-L-E-U-M. Now, spelling
in anatomy always counts. And ileum is a word
that it is easy to forget that it is an E
in the word ileum, especially since there
actually is a bone in your pelvic
girdle called the ilium, but it’s spelled different,
it’s spelled with an I. so the ileum, the ileum has an E
because you eat food that goes through your ileum
with an E, piece of cake. The ileum is the longest,
it’s over 10 feet long. The jejunum, I think, was seven
and a half feet long. Dude, the small
intestine is huge. It’s really long,
and what’s happening in here? There are two primary events that are taking place
in this whole thing. Number one, chemical digestion, and number two, absorption. Chemical digestion,
we’re dumping in enzymes, most of the enzymes are
dumped in the duodenum. Enzymes and other
juices enter here. And when we look at our
accessory structures, like the pancreas and the liver, check it out,
you can even see it. We have ducts from the liver
and gall bladder. And from the pancreas, and those ducts jump juice
into the duodenum. And the juice
that they’re dumping is full of digestive enzymes
that help you break down the food that’s
been mechanically churned in your stomach
and chomped in your teeth, and now we need to break it down with chemicals
so that it’s really, really simple and small. So then you can actually
absorb it into your bloodstream. And that’s the small intestine,
that’s its job. Now, if the job is
to chemically digest, then it makes sense
that we’re going to have a place where we can dump chemicals in,
and that’s in the duodenum. It also makes sense
that we would have time to do that chemical digestion,
and in order to have the time to carry out
the chemical breakdown, the small intestine
better be pretty long, like your food better stay
in the small intestine for a relatively
long period of time. And it does because dude,
that thing, the length of the small
intestine is huge, so it takes a long time
to get through the whole thing, which gives you a lot of time
to do the chemical digestion. If you are going to be
an efficient absorber, then it makes sense
that we would have as high a surface area
in lining the lumen of our tube as possible. The more surface area you have,
the more area, the more surface area you have to actually absorb
the substances into your body. So, there are several ways that the digestive system deals
with this surface area issue. First of all, you have more
surface area if you’re long. So, the length of the small
intestine contributes to its ability
to increase the surface area and be more effective
at absorbing nutrients. The small intestine also has the structures called
circular folds, and you can’t see them
in this image right here. I’m wondering if I have
any images where you can see it. But a circular fold,
here’s my tube, you got it, and a circular fold is just
a place where the tube narrows, and then it gets bigger again. Okay, I have to draw you
a picture. Because look
at how a circular fold works, we make our digestive tube,
look at this. Here’s my tube,
and then it narrows down and then goes back
to the original size. That’s the circular fold. It’s kind of a big,
and gosh, this kind of makes it
look like it has, you know, one
finger that’s coming out, but that is supposed
to be one whole tube, with these kind of constrictions
around the whole tube. So, if I went and looked at it,
I actually would see that, you know, this part of the tube
would have to be this big, but this part of the tube I
could actually like fit a tiny little rubber band
around it, because it’s actually narrower. But then you look at that,
and you’re like oh, dude, that’s awesome, because look, I now have an
increased surface area, that as opposed to just that.
Makes sense, right? Okay, so the circular
folds are another way to increase the surface area. You also have structures
all through the small intestine called villi, and this is really
interesting, too. So, watch in addition
to your circular fold, which is the entire tube, narrowing, lining the tube
itself all the way along, even in the narrow parts. Okay, so I’m going to take a
cross section right here and I’m going to draw you a
picture
of the tube from this aspect, from a cross section looking
down it, and you actually have
these structures called villi. Whoa, these are all villi. Do you even know
what the world I’m drawing? This is one villus, here’s another villus,
do you see that? These villi are finger
like projections extending into the lumen
of the tube itself. So, the tube narrows, but the tube is also filled with
these finger-like projections that all they do
is increase surface area. Now, there’s one more thing
that increases the surface area. And it’s called microvilli. They are called microvilli, and
I’m going to write it down here. Microvilli increases
the surface area, as well. But now I have to draw you
a big picture. Look, I can even fit it on here. Are you ready? Now, I’m just
going to take a slice, I’m going to take just,
I’m going to take one villus out of this picture. And this is what
I’m going to do. Here’s my single
villus that’s extending into the lumen of my tube. And we know that
the villus is actually lined, what would you think,
by what kind of tissue? Epithelial tissue, right? And we actually looked at this
epithelial tissue, it’s simple columnar ephilium. And so this whole
thing is a villus that whole finger is a villus. Are you ready
to find out the amazing and fantastic microvilli? First of all, do you agree
that this is one cell? Whole bunch of cells make up
my villius. Guess what is on the luminal
end of these cells? What? Little microvilli.
So, let me clarify this, because this makes it
look like they’re not attached. Wonder if I can erase that.
I love this program. Look at that, and every
single one of them has it except I just
didn’t take the time to draw every single one,
but these guys, right, her, those are
my microvilli. And this whole thing is a villus
or plural villi, we have a whole bunch of them
and they all line the lumen. What, so if you’re going
to do a compare and contrast mircro villi
to villi, villi are made of multiple cells
they’re an entire structure sticking into the lumen
of a tube. microvilli are similar
little extensions, but they come off
of a single ephitelal cell. And we should be able to see those when we look
in the microscope and do some digestive histology. Okay, we’re going
to talk about the accessory structures
later on. So, I feel good
about this treatment of the small intestine. Let’s look at the
large intestine.

8 thoughts on “Digestive System 6- Small intestine

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