Video Transcript
In this video, we will learn how to
describe the structure and function of the digestive system, including the parts of
the mouth that help us to digest food. So we’re really thinking about the
journey that our food takes when we eat it and the special organs that help with the
process. This is called the digestive
system.
We should recall that our bodies
are made up of lots of different systems that have different functions. For example, we have the nervous
system, the circulatory system, and the respiratory system. Each body system is a group of
tissues and organs that work together for a certain function. The digestive system is the
same. And its function is to digest and
absorb food. In fact, the word digestion simply
means the process of breaking down food.
So let’s think about the different
parts of our digestive system. Our food begins its journey through
our bodies by entering our mouths. Even before we start eating, our
salivary glands are starting to work at the prospect of eating food. The saliva will help moisten our
food before we swallow it through our pharynx, which is part of the throat. The food travels down through the
esophagus to the stomach. The pancreas and liver help to
provide the chemicals our stomach needs to break down the food into the useful
nutrients that our bodies can use.
The chewed-up food, mixed with the
saliva and the chemicals from the liver and pancreas, travels through the small
intestine and large intestine. They absorb more nutrients from the
food, leaving waste products to pass through. They are then excreted, that means
passed out, of the body through the rectum and anus.
We can classify the different parts
of the digestive system into those that are part of the digestive canal and those
that are not. The digestive canal is the long
tube in the body that starts at the mouth and ends at the anus. It is where food is broken down and
absorbed for use by the body. So the parts of the digestive
system that are part of the digestive canal are those that the food passes
through. They are the mouth, pharynx,
esophagus, stomach, small intestine, large intestine, rectum, and anus. The parts of the digestive system
that are not part of the digestive canal are called the supplementary
structures. They are the salivary glands, the
liver, and the pancreas.
So now that we’ve seen some of the
parts of the digestive system, let’s see an example question to check what we’ve
learned so far.
Which of these is not part of the
digestive canal? Option (A) the large intestine,
option (B) the small intestine, option (C) the stomach, or option (D) the liver.
Let’s begin by recalling that the
digestive canal is the long tube in the body that starts at the mouth and ends at
the anus, where food is broken down and absorbed for use by the body. The broken-down food passes through
the stomach, the small intestine, and the large intestine on its journey through the
digestive system. These three organs are all part of
the digestive canal.
The liver is a part of the
digestive system. And it’s an organ that helps to
provide some of the chemicals that our stomach needs to break down the food into
useful nutrients that our bodies can use. However, it is not a part of the
digestive canal. We say that it is a supplementary
part of the digestive system. Therefore, we say that it is the
liver which is not part of the digestive canal.
We’ll now look a little more in
detail about the start of the digestive process and how important our teeth are in
breaking down the food that we eat.
We know of course that when we eat
our food, we have to chew it. Otherwise, it would be too big to
eat and we’d choke. Chewing helps break the food down
into smaller pieces that are easier to digest and swallow. But not all of our teeth do this in
the same way. This is why our teeth are different
shapes and sizes.
Let’s look at this diagram of an
adult’s teeth, which is colored to show the different types of teeth that we
have. The first thing we do when we take
a mouthful of food is we bite the food with these teeth at the front of our mouth,
colored here in green. These are called the incisors. We have four incisors in each
jaw. That’s four at the top of our mouth
and four at the bottom. Incisors help us bite, tear, and
cut food.
The teeth next to the incisors are
called canines. They also help us tear food. Have you ever eaten a bar of tough,
sticky candy? Our canines are strong, sharp, and
pointed to help us tear through it.
When we eat our food, we also need
to use our molars at the back of our mouth. Our molars have a flatter surface
than the incisors and canines and are the teeth that are best at grinding food. If we were eating peanuts, for
example, we wouldn’t use our incisors at the front to grind the peanuts; we’d use
our molars.
Now, let’s consider another part at
the beginning of our digestive system which isn’t part of the digestive canal. Do you remember it? It’s the salivary glands.
The salivary glands are the organs
in your mouth that secrete saliva. That means they produce the
saliva. There are three pairs of salivary
glands in the mouth. So what purpose does the saliva
have? Well, firstly saliva moistens our
food. That means it’s much easier to move
the food around our mouth. And it’s easier to swallow the food
because the saliva helps to lubricate the mouth and pharynx.
But saliva has other functions
too. Saliva helps break down the
molecules in food into simpler substances. And that’s because saliva isn’t
just water but contains molecules that break the food down. If you eat some bread, for example,
that bread contains starch. Starch is converted into sugar,
which is simpler for our bodies to use. And that process is begun by the
digestive enzymes in saliva. And by the term digestive enzymes,
we simply mean the molecules that break down food, like starch, into simpler
substances, like sugar.
Now let’s see an example of a
question about how the mouth plays a part in the digestive system.
Amer and Dalia are talking about
what role the mouth plays in digestion. Amer says, “The mouth secretes
saliva that contains digestive enzymes.” Dalia says, “The mouth breaks down
food by cutting, tearing, and grinding through the work of teeth.” Which student is correct?
We know that the mouth plays a
number of different roles in digestion. Salivary glands are found in the
mouth. And they excrete a liquid called
saliva. Saliva is an important part of
digestion because the saliva contains enzymes which break down food, like starch,
into simpler substances, like sugar. So we can see that Amer is correct;
the mouth does secrete saliva.
Let’s think about what Dalia
says. The mouth breaks down food by
cutting, tearing, and grinding through the work of teeth. Teeth are an important part of the
role of the mouth in digestion. So Dalia is also correct. Since both of the statements are
true, we can give the answer that both students are correct.
Before we finish with thinking
about the role of the mouth in digestion, there is one other part of the mouth which
also helps food on its digestive journey: the tongue. We might not have thought that our
tongue helps us digest our food. It’s great for tasting our food,
but how does it help digest it?
Well, firstly, the tongue helps
push the food around our mouth. That then allows our teeth to tear
and grind the food into smaller pieces. The tongue also helps mix our food
with saliva, which allows all the digestive enzymes to start mixing and working. Finally, our tongues help with
swallowing our food.
Let’s now see a question that will
check our understanding of what the tongue does in the body.
Which of these correctly describes
the role of the tongue? Option (A) it turns food in the
mouth. Option (B) it helps us taste
food. Option (C) it helps mix food with
saliva. Or option (D) all of the answers
are correct.
We know that the tongue plays an
important part in more than one way. We know that it does turn food in
our mouths. Our tongue moves the food around to
help our different sorts of teeth cut, tear, and grind the food into smaller
parts. The tongue does allow us to taste
food. We don’t need to taste food in
order to digest it, but this is one of the roles that the tongue has. We also know that the tongue does
help mix food with saliva. The enzymes in saliva will begin
the process of breaking down food into useful components even before we swallow
it. The tongue is also important for
swallowing food.
Each of the statements in the first
three options are correct. The correct response is option (D);
all of the answers are correct.
We’ll now recap what we’ve learnt
in this video.
Firstly, we learnt that digestion
is the process of breaking down food. We also saw that we can describe
the digestive system as being made up of two parts: the digestive canal and the
supplementary structures. We’ve labeled the parts of the
digestive canal on the left of the diagram. On the right of the diagram, the
supplementary structures of the salivary glands, liver, and pancreas do not form
part of the long tube of the digestive canal but still have a very important role in
digestion.
Digestion begins with the
mouth. In the mouth, teeth play an
important role at the beginning of the digestive journey. In each jaw, an adult has four
incisors and two canine teeth, which help with cutting and tearing, and 10 molar
teeth, which are important for grinding food. As part of the mouth, we have
salivary glands which excrete saliva. The digestive enzymes in saliva
break down starch into sugar.
Finally, we saw that the tongue
plays an important part in digestion. Our tongues push food around the
mouth, mix the food with saliva, and help us swallow food.
And so we have seen what the
digestive system does and how different parts of the mouth help with this
process.
