– Hello, everybody. Today, we are going to talk
about the digestive system, and we are going to start out
with our study of the gross anatomy
if the digestive system by looking at some of
the functions of the digestive system. So, let’s get started
making a list of functions. I have six primary functions,
and I’m actually– I can’t help it.
I have to draw you– even though I have this lovely
picture right here, I could use this picture,
but you know what? We’re going to get
into the anatomy of all of these parts
and who these people are and what part is
what in way more detail than we’ve got going on here.
But I can’t help it. I have to draw you a picture
of your own digestive tube. Does this look familiar? You know it does.
We did this. We drew this body when we were
talking about epithelial tissue. Remember that?
And remember how I had, oh, what is this?
A smiling happy mouth. And what is this? I’m going to make it
look like a sphincter. Dude, I’m not even going
to talk about that. That’s your anus.
This is your digestive tube. We’re going to name all of
the parts in this lecture, but I’m going to draw you a
picture of all of the functions of the digestive system,
and we’re going to start with the first one, which
is basically ingestion of food particles
into the mouth. One of the jobs of the digestive
system is to ingest food. That makes sense, doesn’t it?
Imagine that. And, look, I even
drew it for you. Guess what?
Another function–okay. I have to draw you a piece
of food that came in. Another function of the
digestive system is to digest the food. Really?
True story. What is digestion?
Well, basically, when you digest something you break it
down into littler parts. How great is this?
Look. I’m even going to label these.
Ingestion, this was number one. Digestion, this was number two.
I broke it down into pieces. In our digestive
system there are two ways that we break things down. We can break things
down chemically, or we can break them
down mechanically. That says mechanically. Of course it does. When you break something
down chemically, you actually add a chemical to it and the
chemical breaks the chemical bonds in the original substance,
creating smaller particles. That’s what digestion is. When you break something
down mechanically, you actually apply a force to
break the particles apart. The end result is
exactly the same. You end up–you start out
with a big particle. You end up with lots of little
particles, which, again, is the definition of digestion. A third thing that happens
in the digestive system– I’m going to draw it
in a different color. The digestive system, the whole system moves
substances through it. So it’s called motility. But basically, you’re moving the
particles through the GI tract. So, look.
I’m going to draw it like this. This is number three.
These particles move, and I’m going to try to make
my little purple particles. They just move through
the digestive tract. As we examine our entire system, we are going to see
the different parts of the tube, and we’re going to name all of those different
parts of the tube, and we’ll notice
that different parts of the tube have different
functions. Like, different things are
happening in each of the parts, but we have to move the food
through the tube in order to get from the start
to the finish, which makes complete sense.
Of course it does. We also have– oh, I love this one– another function is secretion, and it’s probably a good idea– we’re going to see secretion
in lots of different scenarios. Secretion is when, like,
body cells– this is familiar to you,
I know. Epithelial cells lining
the lumen of my digestive tube, actually are
producing substances, digestive chemicals,
mucus, other enzymes, even sometimes
some waste products are actually secreted
into the digestive tubing, but when a substance is moved
from the inside of the body into the outside, into the tube,
that process is secretion. Are some of these familiar? They are totally functions
of epithelial tissue, which is what
the tubing is lined with. All right.
Number five, why are we doing that?
Why digestive system? Why?
Because you are hungry. Your cute little
cells are starving. And so another function of the digestive
system is absorption. Again, hopefully familiar,
because this is actually a function of the epithelial
tissues themselves. So, once you break down
your chemicals, your food, it gets digested
into smaller pieces. What is the point of breaking it into smaller
pieces in the first place? Well, your cells actually cannot
use the hamburger directly. Your cells have to use
the molecules in the hamburger. They can’t make energy that you can use out of
an entire hamburger. So, break it down. Don’t leave it in the tube,
because guess where the tube is going. Yeah.
That direction. Anything you leave in there is
going to end up in your toilet. Hopefully it’s your toilet. I don’t really want
to think about that too much, but anything that we want,
we better get it out of there through the process
of absorption. That’s handy. And then anything that’s
left over, yes. The things that are left over– so we’re going to take
the little purple squares, and anything that’s left,
we are going to eliminate. Elimination. Interestingly, the way
we eliminate stuff in the digestive system is by
going poo-poo through the anus. So, literally, diarrhea.
Diarrhea is awful. And you can– it’s a huge issue
if you have diarrhea and you can’t
get it under control, because you actually
are going to poop out all of your nutrients. You are going to eliminate
all of that stuff before you can absorb
the good stuff. You can’t absorb
the water back in. You can’t absorb the nutrients back in because you are
pooping it out so fast that it is gone
before you can absorb it. Those are all– that’s a big picture overview
of our functions of the digestive system, and now
we are going to break down each individual part of our tube and talk
about the unique features found in that part of the tube, and some of the anatomical
features, and then some of the functions
in each part.