Lesson video

This lesson is called "The Parts of the Human Digestive System," and this is from the unit "Human Digestive System." Hi there.

Welcome to the lesson.

My name's Mrs. McCready and I'm here to guide you through today's lesson.

So let's have a look at what we're going to be covering.

In our lesson today we're going to learn about the parts of the human digestive system and see how they were adapted to digest our food.

In our lesson today, we're going to cover a number of keywords.

Now they're listed on the screen here and we're gonna come across each of them one by one.

I'll introduce them to you as we come across them, but if you would like to pause the video and write them down or write the definitions down, then please do so.

So in our lesson today, we're going to learn about the parts of the human digestive system.

We're going to start off by having a look at what parts make up the human digestive system.

Then we're going to have a look at the adaptations of organs, glands, and tissues within that system, before we finally look at what happens to our undigested food.

So I hope you're ready to get started.

I am.

Let's go.

Before we carry on and have a look at the parts of the human digestive system, we need to understand that our food is our source of energy.

If we don't eat, we won't have energy and it won't be long before we won't be able to live.

So food is really, really important to make sure that we have all the energy that we need in order to carry out our daily life processes.

But food is much more than just a source of energy.

It is also our source of materials that we need for growth and repair.

So let's say you've fallen over and hurt yourself in the playground, broken a bone, or something like that, or maybe just general, day-to-day wear and tear of your body, like your skin sloughing off, your body will need to repair itself.

And in order to get to the materials that it needs in order to repair itself, we need to consume food because that's where those materials are coming from.

Also, as teenagers, you are growing and you need some of the nutrients that you get from your food to build your body as it grows.

So food is a really important source of energy, but it's also a source of materials for growth and repair.

Now, we can't just take the food that is on our plate and slap it on our arm if we want to build a bit more muscle or put it over a cut if we need to repair our skin.

So what we need to do is break that food down into really small nutrients that can then be absorbed, moved around our body, and used where they are required.

And it's that process of breaking large pieces of food down into absorbable nutrients, that is called digestion.

And that's what we are looking at in this module.

So let's just quickly check our understanding.

Which student gives the most accurate description of what we need food for.

So Laura says, "Food gives us energy so we can grow." Andeep says, "Food has to be digested to get the goodness out." And Izzy says, "Food allows us to live." So I'll give you five seconds to have a think.

Who gives the most accurate description? Well done if you said Laura.

So Laura's description, that food gives us energy so we can grow, is the most accurate of those descriptions.

So the digestive system is a group of organs that digest our food.

And food moves through these organs, through the digestive system in a very particular order, starting at the mouth, moving down the oesophagus into the stomach.

And after a while of being in the stomach, it moves out into the small intestine before waste products move into the large intestine, before being stored in the rectum and digested, passed out of our body via the anus.

That's a very specific order.

Mouth, oesophagus, stomach, small intestine, large intestine, rectum, and finally the anus.

So what I'd like you to do now is have a think and sort these three parts of the digestive system, starting with the first, into digestion order.

So which one comes first? Your options include the large intestine, the stomach, and the small intestine.

I'll give you five seconds to think about it.

Ready to check your answers? Okay.

Well, well done if you put the stomach first, followed by the small intestine and then the large intestine.

Excellent job.

So what I'd like you to do now is to label the diagram to show the main organs of the digestive system.

So the digestive system labels are listed there and you need to attach them to the right parts of the sheet.

Pause the video and come back to me when you're ready.

Okay, have you done that? Let's have a look and check our answers.

So you should have put your labels in roughly the same places as I have on my diagram.

So just check your work over and make sure that there thereabouts the same, that you've got the correct organs labelled up properly, and make any amendments if you need to.

Next, I'd like you to start with the mouth, complete the flow chart to show the correct order that food moves through the organs.

So, which order does food move through? Have a think, pause the video, and come back to me when you're ready.

Okay, ready to check your work? So we're starting at the mouth, then we're moving through the oesophagus, then to the stomach, then the small intestine, the large intestine, the rectum, and finally the anus.

Did you get them all right? Well done, if you did.

Okay, so we've seen which parts make up the human digestive system.

What I want to have a look at now are the adaptations of the organs, glands, and tissues within the digestive system.

So the human digestive system is made up of many specialised tissues, organs, and glands.

But what do these words mean? So let's have a look.

So a tissue is a group of one type of cell, like muscle tissue, skin tissue, that sort of thing.

And an organ is a group of specialised tissues all working together.

I expect you're quite familiar with a number of organs such as the heart, lungs, kidneys, liver, and the brain.

But maybe this word gland you haven't necessarily come across before, perhaps not had defined for you before.

So a gland is a tissue or an organ which produces chemicals, and it secretes or releases these chemicals into the system that they're working with.

So in this case, the digestive system.

Now you probably have come across a gland, the salivary glands in our mouth.

The salivary glands are located underneath the tongue and in our cheeks and they secrete, release saliva into the mouth.

So that's an example of a gland and we'll come across some other examples in the rest of this lesson.

So let's have a look at what this word adaptation means, because the term adaptation is a really important term within biology, and it'll come up time and time again as you work through your biology syllabus.

So an adaptation is a feature that helps an organism to function and survive.

So every organism is adapted to function and survive in the environment that it lives.

And many organisms have sort of sub-adaptations where bits of their body are designed to carry out very specific functions within that organism.

And when you put them all together, that helps the whole organism to survive.

And the digestive system is an example of this.

It's a collection of organs which are specifically adapted to digest and absorb food and process waste.

And they work together to help us, as an organism, to survive.

So each of our organs within the digestive system is adapted in its own unique way to digest the food as it receives it.

So let's have a look at some of those adaptations.

Starting with the mouth.

The mouth has several adaptations, and I'm sure you can think of quite a few.

For instance, the teeth cut and chew food into smaller pieces, and there are lots of different types of teeth within our mouth which each have their own specific role.

Also within our mouth we have the tongue, and the tongue rolls and mixes our food around in our mouth and prepares it so that we can swallow it.

But all of that is made much more easy by the salivary glands because the salivary glands release, or secrete, chemicals in saliva, chemicals and water in saliva into our mouth and that helps us move our food around the mouth and prepare it to be swallowed.

So I don't know if you've ever had to go at eating food with a really dry mouth, but it's very, very hard to do.

And adding saliva, adding water and chemicals to help move the food around and help to start digestion is really important.

Once we've swallowed our food, it moves down the oesophagus.

So this is a tube which connects the mouth to the stomach.

Now food moves through the oesophagus because it has rings of muscle which contract behind the bolus of food.

So the bolus is just the lump of food that we've just swallowed.

And these rings of muscle contract behind the food, to the bolus of food, to push it down the oesophagus towards the stomach and make sure that it keeps moving in the right direction, down towards the stomach.

That process of contracting and pushing the food through the oesophagus is called peristalsis.

And that process isn't unique to the oesophagus.

It also appears within the small and large intestines to help move food nutrients and waste products through the digestive system in the correct direction.

So let's quickly check our understanding.

So which of these describe the function of the salivary glands? Do they produce chemicals for digestion? Do they roll and mix food in the mouth? Or do they add water to food? I'll give you five seconds to think about it.

So, did you spot both correct answers? That the saliva glands both produce chemicals for digestion and add water to food? Well done, if you did.

So let's have a look now at what happens in the stomach.

How has the stomach adapted to digest our food? Well, the stomach is a bag which receives recently swallowed food and it produces hydrochloric acid, which enables the food to be digested and also kills pathogens.

So, pathogens are invading microorganisms, so really small organisms, which are there to cause us disease.

And the hydrochloric acid that the stomach releases helps to digest the food but also kill off those pathogens and keep us healthy.

After the food has spent some time in the stomach, it's moved into the small intestine.

And the small intestine is a long narrow tube which slows the passage of food down.

So if you think about a lot of people in a big room all trying to leave at the same time, if they passed out through a really, really big, wide door, then they'd be able to leave the building really, really quickly.

But if we funnelled them through a small door, a narrow door, then their passage out of the building would be much, much slower.

And it's this idea that is, in principle, in small intestine because the small intestine is long and narrow and that helps to slow the food down.

That means that the food can be fully digested and it also slows the food down so that by the time it's become nutrients after it's been digested, all of those nutrients can be fully absorbed rather than passing through our body really quickly.

So that's a really important adaptation of the small intestine.

But the small intestine also has another adaptation, and that's because the surface of the small intestine has all of these tiny structures protruding, sticking out of its surface, called villi.

You can see them in the diagram there, all these finger-like projections called villi sticking out into the small intestine.

And these villi are where absorption takes place.

So food in the small intestine passes through the villi into the blood.

And all of these villi help to make sure that all that absorption happens really efficiently.

And once those nutrients are in the blood, they can then be transported around the body to all the living cells so that they can use those nutrients for energy and for growth and repair, as required.

There are a couple of other organs that we need to have a look at as part of our focus on the human digestive system.

And the first one is the pancreas.

So the pancreas is an organ, but it is also a gland.

Can you remember what a gland is? So, a gland secretes or releases chemicals.

And in this case the pancreas releases those chemicals into the small intestine.

And these chemicals are really important at helping to break down the food into nutrients.

But it's really important to understand that the food doesn't pass into the pancreas and back out again.

The pancreas secretes the chemicals that it makes into the small intestine, which is where the digestion takes place.

So food isn't moving through the pancreas.

The pancreas is secreting chemicals into the small intestine.

The other organ that we need to know about is called the liver.

And the liver is an organ, but it is also, like the pancreas, a gland.

So it also secretes chemicals into the small intestine.

And the chemicals that it secretes are called bile.

Now bile is really important because it helps to break down fat and make it be able to be suspended into water.

So if you've ever seen water and butter together, or maybe you've mixed some vegetable oil and water and given it a bit of a shake, you'll see that they don't mix.

They might mix temporarily.

Oil and water might mix temporarily, but they'll soon separate out.

And this is because water and fat hate each other.

Fat is water hating.

And in order therefore to get fat to be suspended in water, to be soluble in the blood, it has to be surrounded by bile.

So bile has two purposes.

It firstly breaks fat down into really small blobs, globules, and it also surrounds those tiny particles so that the fat particles can be suspended in water.

But just like the pancreas, the liver doesn't get food passing through it.

The liver secretes its chemicals, the bile, into the small intestine.

The food doesn't pass into the liver and back out again.

That's really important to understand.

So a quick check of understanding.

Which of the organs listed does food not pass through? So food does not pass through some organs in the digestive system, but which ones does it not pass through from the list? So the options include stomach, small intestine, pancreas, and the oesophagus.

I'll give you five seconds to think about it.

Have you worked it out? Did you say the pancreas? If you did, well done.

What I'd like you to do now is to draw lines to match the adaptation on the left to the organ on the right.

So which adaptation is a feature of which organ? Pause the video and come back to me when you're ready.

Okay, let's mark our work.

So you should have matched the teeth to the mouth, peristalsis to the oesophagus and the salivary glands to the mouth.

Well done if you did.

Next I would like you to draw lines between each column of boxes to make three sentences about digestion.

So the first line has been drawn for you, "The pancreas secretes chemicals." But how do you finish that sentence and what are the other two? So pause the video again and come back to me when you're ready.

Okay, let's mark our work.

So you should have said that "The pancreas secretes chemicals to digest food." "The liver secretes bile to break down fat." And, "The small intestine absorbs nutrients into the blood." Did you get them all right? Well done if you did.

Okay, what I'd like to move on to lastly then is have a look at what happens to undigested food in the digestive system.

What do we do with our waste? So the large intestine receives all the parts of the food that cannot be digested and absorbed by the small intestine.

So this is anything that has not been broken down by the processes in the small intestine and hasn't then been absorbed.

All of these parts of our food get moved into the large intestine from the small intestine.

Now this, really importantly, includes fibre.

Now fiber's a really important part of our food, of our diet, but it cannot be digested and absorbed.

But it's important because it helps to bulk our food up and provide it with substance that enables the digestive system to move our food, and importantly the waste food, through the digestive system and out of our body.

So the unabsorbed waste, including fibre, moves through the large intestine and it is finally passed out of our body in the form of faeces, or poo, when we go to the toilet.

As the waste moves through the large intestine, water is absorbed into the blood.

This is really important as well because water is a really important commodity in our body.

It's really important resource.

And we don't want to waste all of the water that we have consumed.

So a lot of the water that is in our waste products in the large intestine gets absorbed again.

Not all of it, but quite a lot of it does.

And this helps to dry out the food and bulk it up so that it's firm enough so that it can be pushed out of the body easily.

And the faeces, the waste products, the faeces are stored in the rectum until we're ready to defecate.

That means to get rid of them out of the body.

Once we are ready to defecate, the faeces are pushed through the anus.

And the anus is a ring of muscle, which helps to control the exit of faeces and other waste gases from our body.

So when we go to the toilet, we push waste which has been stored in the rectum out through the anus and out of our body.

So quick check of understanding.

The function of the large intestine is to absorb what? Your options include, fibre, food, and water.

I'll give you five seconds to think about it.

Okay, let's check your answer.

Did you choose water? Well done, if you did.

And one more check of understanding.

Is this statement true or false? "Fibre is absorbed in the digestive system." Don't forget to justify your answer.

I'll give you five seconds to think about it.

Okay, so, "Fibre is absorbed in the digestive system." This is false.

Fibre is not absorbed in the digestive system.

And the reason is that fibre helps move food through the digestive system, but it cannot be absorbed.

Well done if you've got both of those right.

What I'd like you to do now is to use the words in blue to complete the sentences to describe what happens to undigested food.

So pause the video, take your time, read over your work to make sure that it makes sense, and come back to me when you're ready.

Okay, let's check our work.

So as you are marking your work, just make sure that you've got the correct words in the correct locations and if you've made any mistakes, then just amend your work so that it's fully correct by the time you've finished.

So, you should have said that fibre bulks up food so that it can be moved through the digestive system by the process of peristalsis.

It is not digested, but forms faeces, which are passed out of the body via the anus.

It is stored in the rectum until you are ready to defecate.

Did you get them all right? Well done, if you did.

What I'd like you to do now is to have a think about a meal and consider the fact that it contains nutrients, water, and fibre.

So maybe you can consider the meal that's on the slide there, or maybe your favourite meal that you really enjoy eating.

And what I'd like you to do is to describe the journey of this meal through the digestive system.

So, I'd like you to really consider this.

Pay a lot of attention.

Spend quite a lot of time on this task and include as much information as you can, including information about the parts of the digestive system, and particularly list them in order, how they're involved in digesting this food, and their adaptations.

And also think about what will happen to the different parts of the meal once they've been digested.

Where do they go? So this is a long task.

Take your time.

Use all the keywords from the lesson and also all those organs that we've looked at.

Really spend quite a lot of time considering this.

Read your work over thoroughly.

Pause the video and come back to me when you're ready.

Okay, I am gonna give you a guide to what you might have included.

So you might have written, the organs of the digestive system, preferably listed in order.

You may have included the roles of the liver and the pancreas in digestion.

You might have written about the role of peristalsis in moving food through the digestive system.

You should have said that nutrients from the food are absorbed into the blood through the villi in the small intestine.

And that water from the food is absorbed into the blood through the wall of the large intestine.

You may also have included that fibre from the food is not absorbed and is passed out of the body as faeces.

So take some time to review your work against this mark scheme, add anything in that you've missed, and well done.

That was a really hard task.

So in summary from today's lesson, we have seen that the digestive system breaks down food into nutrients that can be absorbed into the blood.

And we've seen that this process is called digestion.

Now each part of the digestive system is adapted to digest our food, and food passes from the mouth down the oesophagus into the stomach.

But most digestion occurs in the small intestine.

We've also seen that the pancreas and the liver are organs with glands which secrete chemicals to digest our food.

And once digested, the nutrients are then absorbed into the blood.

Waste products, which include fibre, then continue on into the large intestine and form faeces.

And these faeces are stored in the rectum and passed out of the body via the anus when we defecate.

So I hope you've enjoyed today's lesson.

Thank you very much for joining me and I hope to see you again soon.

Bye.