Hi there, I'm Mrs. Kemp, and welcome to today's lesson all about non-specific defences of the human body against pathogens.

This fits into the "Defence against pathogens, the human immune system and vaccination" unit.

So let's get started then.

For today, we have a main outcome.

This is, I can describe defences of the human body against pathogens, including physical, chemical, and microbial defences, and phagocytes.

We've got some key terms that we'll be using today and you may not have heard some of them, so if you want to pause the video and have a read of them, please do that now.

Otherwise, do rest assured that I will go through each one of these as we move through the learning cycles.

We have two learning cycles for us today then.

We've got physical, chemical, and microbial defences and also phagocytosis.

We of course will be starting with that first one, physical, chemical, and microbial defences.

So as human beings, we actually come into contact with around 60,000 microorganisms every day.

They're literally everywhere.

They're on all of the surfaces that we touched, on our food, everything.

So why is it that we don't get sick all the time? Have you got any ideas? Well, actually, it's because first of all, not all microorganisms are pathogens.

So we live very easily with other types of organisms all the time and they don't cause us any problems. We've also got defences to help prevent pathogens from actually getting into our body, and you might know some of those already.

And we also have an immune system to protect us against any pathogens that have actually made it into our body.

So they've gone through our first line of defence and they've actually made it inside.

So we're going to have a think about some of those different techniques of how we keep pathogens out of us.

And the first ones that we're going to look at then are the body's physical defences.

So like our barriers to prevent the pathogens from getting in.

The most obvious one covers our whole body nearly, and that's our skin, okay? And if our skin gets damaged, that would be a way that pathogens could then enter our body.

So if we fell over and cut ourselves, then pathogens could enter in that place.

But actually, our body's really clever and it's able to heal itself.

We've got things called platelets in our blood, and platelets stick together.

And what they do is they form a blood clot so that it actually seals the area and you'd be able to see that when you've got a scab.

So let's say you've fallen over again and it's healed itself with a scab, that is where those platelets have started to stick together in order to prevent the entry of those pathogens.

Anywhere that our body is not covered with skin then, that's going to need some other sort or form of defence.

So for example, in our nose, okay? Not our whole nose is covered with skin.

Otherwise, we wouldn't be able to breathe.

All right, so we have got an entry point there for any pathogens.

Inside your nose, you've actually got some tiny little nose hairs.

They've got a really important job.

What they do is that when we breathe in, it kind of filters the air and traps any dirt and dust that's in the air, which potentially then contain the pathogens and prevents those from being taken down into our gas exchange system.

We've also got mucus, okay, and that mucus will also help to stop the dirt and dust from going down into our airways.

And we can blow that out, that mucus, to remove that dirt and dust from our passageways.

If there is some dirt and dust, then, that does manage to get down into our gas exchange system, actually, all the way down our trachea and down into our smaller tubes of like the bronchi, we've actually got these two different types of cells that line the airway, okay? And those are called ciliated cells and also goblet cells.

The goblet cells, what they do is that they actually produce a mucus.

Again, just like we've got a mucus being produced in our nose, we also have a mucus being produced in our gas exchange linings.

And what they do is it traps all that dirt and dust again from the air that we're breathing in.

And then there are these ciliated cells, these ones that have got little finger-like projections on the top of them.

And what they do is that they rhythmically beat that mucus up your trachea into your throat and then you can swallow it.

It goes down into your stomach, okay, where you've got stomach acid, which will then kill any pathogens that you've got in there.

Now these cilia are very, very dainty and actually, they can be damaged quite easily.

And if you are a smoker, smoking can damage those cilia.

And what that means is, is that they're not as easily able to waft the mucus out of your trachea and therefore, the mucus almost gets held in place and actually holds the pathogens into your airways and therefore, you're much more likely to get an infection.

So it's very important not to smoke in order to not damage these ciliated cells.

This type of defence then, this is known as a physical defence.

Okay, can you match the part of the body to the defence? We've got skin, nose, and trachea and then we've got ciliated cells and mucus, scab formation, and hairs and mucus.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you match up skin with scab formation, nose with hairs and mucus, and trachea with ciliated cells and mucus? Brilliant.

Well done.

Okay, so as well as those physical defences, we also have some chemical defences that we can kill pathogens before they get inside us.

So we've got eyes that produce tears, and inside those tears, you've actually got special kinds of enzymes that are called lysozymes.

And what they do is that they're actually able to kill the pathogens.

We also find those lysozymes in our saliva.

So we've also got another chemical defence there in our mouths.

Now we've already mentioned this second one here, that actually inside of our stomach, we've got hydrochloric acid.

And so anything that's in our food or when those ciliated cells have moved that mucus up out of our trachea and we've swallowed it, actually, that's also going to help to kill pathogens that may try to enter into our bodies.

We've also got trillions of microorganisms all over our body, like in our skin and also in our small intestines.

And they're really useful for us.

They can actually be fungi, bacteria, viruses, and they're known as the human microbiota, all right? And they live there.

Actually, most of the time, they're very, very helpful to us and that's because one of the things that they can do is that they can compete for space with any pathogens that might try to come and occupy it.

So this bacteria entering the body will try and find a place where it can start to grow and colonise.

However, if there's something already living there, it won't be able to.

And so that's what our microbiota does for us.

The physical and chemical and microbial defences of the human body, then, protect us against many different types of pathogens.

They're not specific and they will actually target any pathogen that actually enters the body.

Onto another check then.

Which are examples of chemical defences? A, human microbiota.

B, noise hair.

C, stomach acid.

Or D, tears.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you realise that it was C, stomach acid, and also D, tears? Excellent.

Well done.

Onto our first task of the day then.

This one is task A.

Please get your worksheet out, as you can record the answers on there.

Smoking can damage the cilia on the cells lining the trachea.

Explain why a person that smokes may be more likely to get lung infections.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, let's have a little look at the answer then.

Goblet cells in the lining of the trachea produce mucus.

This traps pathogens in the air as we breathe in.

The cilia then move the mucus up to the throat so we can swallow it.

The pathogens are killed by the hydrochloric acid in the stomach.

If the cilia are damaged and not able to move the mucus out, the pathogens will be stuck in the trachea and can end up in the lungs where they can cause infections.

I hope you've got all of that down, but if you need to add a bit more into your answer, please feel free to do that now.

Okay, onto our second learning cycle then, phagocytosis.

So if a pathogen actually gets through those physical defences, the chemical and also the microbial ones, we've actually got blood cells that can help to destroy it.

Here, we can see a little blood smear from under a microscope, a light microscope, and we've got our red blood cells there that are very clearly in that pinkish colour.

And then we've also got these little purpley ones that have been stained and these are our white blood cells.

So as part of the mix of what makes up your blood, we've got red blood cells, white blood cells, and we also spoke about platelets earlier.

They also make up your blood.

So blood is actually transported to all parts of the body through the circulatory system.

And we can see the different parts of the circulatory system there.

We've got the heart, haven't we? And then we've got those different types of blood vessels.

It contains red blood cells, platelets, as we've mentioned, that actually help to clot the blood, and those white blood cells.

And you can see there that there actually seems to be two different kinds of white blood cell.

White blood cells are really important.

They make up something called our immune system, okay? So we've met red blood cells in a previous lessons where they carry oxygen around the body, but we've maybe not really focused in on these white blood cells yet.

There are different kinds then.

There's these lymphocytes and phagocytes.

And phagocytes are the ones that we're going to concentrate on during this lesson.

And what they are adapted to do is to be able to engulf and digest and destroy any pathogens that are entering our blood.

This is a process known as phagocytosis.

Similarly to its name then of being a phagocyte, it's able to carry out phagocytosis.

Okay, true or false? Phagocytes are types of red blood cell.

Is that true or is that false? Okay, that one's false.

Can you justify your answer then? A, phagocytes are a type of white blood cell.

Or B, phagocytes are a type of platelet.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you say A? Phagocytes are actually a white blood cell, not a red one.

Excellent.

Well done.

Okay, which system, or systems, are white blood cells a part of? A, the circulatory system.

B, the digestive system.

C, immune system.

Or D, nervous system.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you realise that it was the circulatory system and also the immune system? So that's A and C.

Excellent.

Well done.

Okay, so let's have a look at this phagocyte in a bit more detail then.

So they're actually attracted to pathogens by chemical signals.

So when that pathogen enters the blood, it will give off some chemicals that actually the phagocyte will be able to detect and move towards that pathogen.

When they do that, then, they've got a really great adaptation.

They're able to move their cytoplasm and change shape.

What they do is they engulf that pathogen with their own cytoplasm.

You can see there in the image, in that second image there of that pathogen being engulfed.

Once it does, it encloses that pathogen inside the phagocyte and then it releases enzymes into the little vesicle where it is being held.

These enzymes will break down the pathogen and destroy it, so essentially kill that pathogen.

This type of defence is actually non-specific because the phagocyte was only attracted to the chemicals being given off by that pathogen.

It's not because it's a particular pathogen and it will actually engulf any pathogen that enters the blood.

Okay, which components of the blood are adapted to engulf, digest, and destroy pathogens? A, the red blood cells.

B, the platelets.

C, the phagocytes.

Or D, the lymphocytes.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you realise it was that one there, C? That's the phagocyte.

Excellent.

Well done.

All right.

Onto the last task of the day then, task B.

And you can find this again on your worksheet, so please do open that up and you can record your answers on there.

So I want you to use the words in the list to complete the sentences.

The words are pathogens, phagocytes, platelets.

So a wound in our skin is healed when blank stick together and help blood to clot, forming a scab.

If blank enter our body through the wound, they can cause us to feel ill.

Blank in our blood protect us by engulfing and destroying blank.

And finally, blank are a type of white blood cell.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, should we have a look at what order those words should go in then? So we should have first gap, we should have platelets.

In the second gap, we need to put pathogens.

In the third gap, we should put phagocytes.

In that fourth gap, we should have pathogens.

And finally, we should have phagocytes.

If you've made a mistake, please do correct those.

So there is a second part of this task for task B and this is to draw and label three diagrams to show a phagocyte engulfing and digesting a pathogen.

Again, you can record this on your worksheet and I will give you some time, but if you need more time, again, you can pause the video.

Okay, should we have a look at my diagrams that I drew then? So first of all, we've got that phagocyte and also the pathogen.

So showing that that phagocyte is being attracted towards that pathogen.

The next thing that it does is the phagocyte actually changes its shape and it moves its cytoplasm around to engulf that pathogen inside.

And then in the final image, what I'm showing there is enzymes being released into that little vesicle where we're keeping that pathogen and that is digesting and therefore destroying the pathogen.

So make sure that you've added some labels to your diagram as well because it really does help to show your understanding of that process.

Excellent.

Really well done.

Okay, so we are very near the end of this lesson and we're just going to go through the key learning points together.

So pathogens are microorganisms that cause disease.

The human body has physical defences, such as the skin to prevent infection with pathogens.

Platelets help to seal wounds in the skin.

The human body has chemical defences, such as stomach acid, to prevent infection with pathogens.

The human body has microbial defences made up of the microbiota that can compete with the pathogens to prevent infection.

White blood cells are part of the immune system that protect us against pathogens.

Some white blood cells can carry out phagocytosis to engulf, digest, and destroy invading pathogens.

So we've had quite a lot of new information there about both the physical defences and also our immune system.

So it's been really good to learn that with you and I hope to see you again soon.

Thank you.

Bye.