Voiceover: So the best way to talk about
the digestion process and the duodenum
is to talk about the four major macro molecules
that make up everything in our body,
starting off with protein.
Proteins are just chains of amino acids.
So there's one amino acid and here's another amino acid.
And they're connected by something called a peptide bond.
After proteins we also have
things that are called carbohydrates.
Carbohydrates or carbs and these are just
repeating units of simple sugars attached to each other.
Can you name one simple sugar?
Yeah, I think you said glucose.
Something like glucose attached
to say galactose would be a disaccharide.
This particular disaccharide would be called lactose.
So a single sugar would be considered
a monosaccharide, two of them a disaccharide,
and then a whole bunch would be a polysaccharide.
In addition to our carbs, we also have nucleotides.
And these guys make up our nucleic acid, our DNA,
and they're composed of three major parts.
There's a phosphate group that sits
on a ribose sugar, that I'm drawing here,
this little pentagon, and then right here
you're going to have the base that's present.
This base is the coating part of your DNA,
like adenine or guanine if you've heard those names before.
And then finally, we also have fat.
Fat has two parts to it, it's got this
triglycerol head that has these three
oxygen groups on it and then each
of these oxygens has a fatty acid tail.
So there's one, there's two, there's three.
So three fatty acid tails that are found here.
So now that we know what the main macro molecules are
we can talk about what are the main processes
that are involved in breaking these guys up
so they can be absorbed into our blood stream.
Starting with our proteins, there's going to be
brush border enzymes that are present
to help break our peptide bonds
or the amino acid bond that's present.
So I'll just write peptidases here,
because as you might recall, whenever you
name an enzyme that ends in 'ase',
that mean whatever comes before it is what's broken.
So, a peptide bond is broken by a peptidase.
In addition the pancreas brings along
a couple of important enzymes that
will help break up our proteins.
First of all it's got trypsinogen that's present
as well as some chymotrypsinogen.
But whenever you see 'gen' at the end
of an enzymes name, that means it's not ready
to work yet, that means it still needs one more cut.
or cleavage before it can start
being completely functional.
Well this is where our brush border
comes in handy again, because there's an enzyme
present on the brush border that's called enteropeptidase.
That is specifically present to break down
trypsinogen into it's active form called trypsin.
And the same thing with
chymotrypsinogen into chymotrypsin.
These guys are going to be able to break down
your peptide bond as well.
Just like peptidases are able to do,
but need a little kick or a little cut
in order to start working.
And once we gobble up our proteins
we'll have our single amino acid
sub-units then and be absorbed.
When we get to carbs we notice that the pancreas
is also pretty helpful here as well,
because the pancreas releases an enzyme
that's called amylase that can help
break up the sugar bond or this glycosidic bond
is another name for this link right here
in certain carbohydrates.
The brush border is also helpful here
because they have a whole bunch of very specific
enzymes that break the glycosidic bond between
very specific simple sugars.
For instance, the brush border enzyme know as lactase
can only be used to break apart lactose,
like I've drawn here.
Now the interesting thing about lactose
that I should mention is that when you get
the stomach flu, you've got a bug that's
just sitting in your tummy, it actually can
start inflaming the duodenum wall
and by doing so it can knock off some
of the lactase brush border enzymes.
And so you won't have lactase.
You won't be able to break down lactose.
You won't be able to separate
our glucose from our galactose.
And so temporarily, you're going
to be lactose intolerant.
Most people gain this ability back,
but you can understand now how precious
these brush border enzymes are to us.
They'll help break up certain disaccharides,
the pancreas will do it's job as well,
and eventually you'll just have your simple sugars
that are going to be left over here.
And remember the name for each single unit
is called a monosaccharide.
When it comes the nucleotides the brush border
helps this as well.
The specific enzyme set that we have on our
brush border that helps break apart nucleotides
are called nucleo-, wait for it, -sidases, nucleosidases.
And the reason why we have nucleosidases
and not nucleotidases, is because it breaks
this bond right there, resulting in this
phosphate group sticking on the ribose sugar.
But now we've got our base as a completely
separate unit from the nucleoside.
Finally, when it comes to fat we're going to get
some help from bile, as I mentioned earlier.
And bile, if you recall, comes from our liver
and our gall bladder.
So these guys are going to release some bile
into our duodenum.
They're going to help emulsify or organize our fat.
So I'll write right here in parenthesis organize,
because they're not really involved
in breaking them down, they're there to help
organize our fats.
One of the main things that help us actually
break it down is from the pancreas.
The pancreas releases something that's called lipase.
The lipase comes in and cleaves right about there.
That way each of these single fatty acid chains
break off and so you'll have these three
fatty acid chains that are hanging out right here,
including your triglyceride head
that's going to be a separate unit all together.
Now you've got these four things
that came off this one fat molecule.