Lesson video

Hello there.

My name's Mr. Swaithes, and I'm really looking forward to teaching you today.

Welcome to this lesson on blood vessels, blood cells and the vascular shunt.

It's an interesting term, isn't it? We'll delve into what that means later in today's lesson.

So this comes from the unit anatomy and physiology, the cardio respiratory system, and it's a cracker.

So by the end of today's lesson, you'll be able to explain the structure and function of the different types of blood vessels and blood cells in the circulatory system.

I wonder, could you pause there for a moment and ponder what are the names of those different blood vessels? And what are the names of the different blood cells that we're gonna meet in today's lesson? Have you heard of any of them before? So the key words that we're gonna unpick, the main ones are arteries, veins, and capillaries.

Of course, they're the different blood vessels.

But we'll also be unpicking red blood cells, white blood cells, plasma, platelets.

And when it comes to this vascular shunt, we'll be looking at how arteries vasoconstrict to deny blood flow to a particular organ or body part, and they vasodilate or open up to feed more blood to that area.

For example, working muscles during exercise.

So today's lesson then is gonna be broken up into two parts.

First of all, we're gonna help you understand the different blood vessels, and then I'm gonna explain the different constituents of blood.

So blood vessels first up and then the different parts of the blood or the makeup of the blood in the second part of the lesson.

Let's get going then.

I hope you're ready.

So here we can see those blood vessels that often are illustrated by red and blue lines around the body.

And those blood vessels are like tubes, aren't they? They transport blood around the body, and there's three different types.

So we mentioned them on the keywords already, didn't we? So we've got arteries, they're typically drawn in red.

We've got veins, they're typically drawn in blue.

And then we've got capillaries, and the capillaries are the most important ones 'cause that's where gaseous exchange happens.

I wonder, do you know some of the similarities and differences between these different blood vessels? Well, let's explore them then.

So here we've got an illustration of an artery.

And we know it's an artery because it's got a few features that are common to all arteries.

So it's got a small lumen.

The lumen is the posh term for the hole up the middle.

So the diameter, the bit where the blood can flow through.

They've also got a really thick muscular wall.

You can see multiple layers to that muscular wall on that cross-section, and that's because they carry blood away from the heart at really high pressure.

So arteries always carry blood away from the heart.

And they break off into arterioles.

So you'll have a main artery, almost imagine my arm is a main artery.

And then it breaks off into lots of arterioles, my fingers, that are going to different body parts, different muscles, for example.

And if you feel your pulse at an artery, for example, your carotid artery or your radial artery in your wrist, that's a way that you can measure your heartbeat because you can feel that high pressure within the arteries.

And importantly, that thick muscular wall means that they can vasodilate, open up, and vasoconstrict, close down, to vary where we send our blood due to the circumstances we're in.

So if we were exercising our arms, where would we want more blood? If we were exercising our legs, where would we want more blood? If we've just eaten a huge meal, we're gonna send more blood to our digestive system.

So this is an end on view of an artery and it shows that thick muscular wall and the small lumen, the small diameter pipe hole up the middle.

So like hose pipes, aren't they, all around the body? So Andeep is here to help us, and Andeep says that he remembers A for arteries carry blood A for away from the heart, and that's always.

What's this one then? This isn't an artery, this is a cross section, this illustration, of a vein, and veins have got a number of features.

So they've got a wide lumen, quite a big pipe way hole up the middle.

They've got a thinner muscular wall, and they've also got pocket valves to help prevent backflow.

So you can see that valve there that once the blood's passed through it, the valve will close off and stop the blood from being able to come back where it came from.

And that's really important 'cause veins are operating at a lower pressure because they're further from that heart, they're on the return to the heart.

So they carry blood back to the heart at low pressure.

And they break off into what's called venules.

So you can almost imagine this arm here representing the arteries, and they break off into arterioles.

And then there's some capillaries here where gaseous exchange happens, and then the venules will connect onto the capillaries and those venules join back together to make veins, the main vein that will return blood to the heart.

So let's do a quick check, shall we? True or false, arteries have a thick muscular wall and a small lumen? That's right, that's true.

And can you tell me why? Yeah, arteries always carry blood away from the heart, which means that they're at high pressure, so they need a thick muscular wall.

And they have a narrower lumen compared to veins 'cause the veins are just trying to help that blood get back at a lower pressure.

Next up, what do you think this is an illustration of, if it's not an artery and it's not a vein? That's right, it's a capillary, and capillaries have got some common features.

So they are only one cell thick.

So almost imagine they're like a piece of paper.

They're just so thin that things can diffuse through them.

So they have a very narrow lumen, and that means that they massively slow the blood flow down.

So there's only one blood cell at a time travelling through that capillary, which maximises the time for that gaseous exchange, the diffusion of gases and nutrients to happen.

So oxygen will diffuse in one direction and carbon dioxide in the other.

They're located at the lung.

So of course we've got a huge capillary network surrounding each of our alveoli, which are those tiny air sacks in our lungs.

But then we also have capillaries at the muscle site to try and unload that oxygen into the muscle site.

So here you can see arteries, arterioles, capillaries, veins, and venules all in one diagram that hopefully helps you see that network of pipes.

So let's do another quick check, shall we? So a few students are discussing body systems and I wonder who's correct, is it Andeep? He says arteries always carry blood or oxygenated blood, in fact.

Or is it Jacob who says that gaseous exchange occurs in arteries? Or is it Sofia who says that arteries always carry blood away from the heart? Who was correct? That's right.

It's Sofia, isn't it? Whereas gaseous exchange happens in capillaries, Jacob, and sometimes we have arteries.

So for example, the pulmonary artery, Andeep, is carrying oxygenated blood.

So they're not always carrying oxygenated blood in arteries.

Okay, what have we got here? Well, it's a blood pressure monitor, isn't it, strapped onto somebody's wrist.

It's important to know that blood pressure is the pressure that blood is under.

So it's the pressure that that blood is exerting against the walls of the arteries or the veins.

And there's two different types of pressure.

So the systolic pressure, so that's when the heart's contracting.

So when your heart beats, how much pressure is it pumping out through those arteries? And then diastolic pressure, which is when it's relaxed.

So because there's still blood in the pipes, there's still gonna be a little bit of pressure even when the heart is relaxed.

And actually one of the big markers for ill health or stress or a poor diet is when that diastolic pressure is too high.

So we call it hypertension when that diastolic blood pressure is up over 100 and that's really dangerous.

It's putting your heart under too much strain all of the time.

So you're gonna need to make changes to kind of exercise, diet and nutrition and stress levels as well.

So just to summarise then, blood pressure or BP is the force exerted by circulating blood against the walls of the arteries and against the walls of other blood vessels.

So, remember then V is for veins, and veins have got valves, and these pocket valves have a really important job to do.

So, because veins are carrying blood at a lower pressure often against gravity.

Think about the veins in your legs carrying blood back up to your heart, that's against gravity, isn't it? So they need these pocket valves to help keep the blood flow back in the right direction.

And this is a particular challenge, for example, on a long haul flight, if you sat still for a long time, or if you've perhaps got an injury that means that you can't move your legs around too much.

Broken leg, for example, or myself have got a ruptured achilles at the moment.

So that means that I've immobilised my leg and there's gonna be some blood pooling in my leg.

So I need to try and help get blood back to my heart through the veins as quickly as possible.

Okay then, let's do a quick check.

Which of the following looks like a vein? Is it A, is it B or is it C? That's right, it's C.

So you can see the pocket valve there in that vein, whereas B is actually an end on view of muscle fibres.

You can see the fast and slow twitch muscle fibres there.

And A, of course, is an artery.

So this boy here has started to sweat and the reason that he's sweating is he's doing some exercise, and the cardiovascular system is really important at regulating our body temperature.

The body likes to maintain a steady 37 degrees Celsius and that's known as thermoregulation.

So if we start to exercise and generate heat inside our body from all these muscular contractions, we start to heat up and our body goes, whoa, I don't want that extra heat.

So it starts to get rid of that heat in a couple of different ways.

So when we're exercising then, we need to get rid of that heat and we get rid of it in two ways.

Sweating, we can see that there.

But also sending more blood to the surface of the skin.

So you can see the red cheeks on that boy because he's been running around and his body's going, oh, I need to get rid of this excess heat, so I'll send more blood to the surface of the skin, so the heat can radiate away.

But also from sweating, when the evaporation takes place of that sweat from the surface of the skin, that takes heat with it as well.

And that redistribution of blood is sometimes referred to as the vascular shunt mechanism.

I mentioned that in the title of this lesson, didn't I? So the vascular shunt is where we're shunting more blood to the surface of the skin, and we're also shunting more blood to our working muscles during exercise.

Whereas if you were somewhere in a really cold environment and you weren't doing exercise, you would redistribute that blood to your core to try and help keep you warm.

For example, if you fell and broke your leg at the top of Everest, you wouldn't be able to move to keep warm.

So your body would try and shut down the extremities to hold that heat in your central core area.

And it's why frostbite can set in in those sorts of instances.

So here we've got an illustration of vasodilation in action, so that arteriole is opening up to allow more blood flow through, and that vasodilation happens when arterioles feeding the areas needing more blood dilate, open up, become wider in diameter to increase blood flow to that area.

And when we exercise the arterioles to the working muscles and also to the skin will vasodilate.

So the working muscles to deliver more oxygen and the skin to get rid of excess heat.

Meanwhile, what about vasoconstriction then? Where will that happen? Well, vasoconstriction is where that arteriole that feeds areas not needing so much blood constrict or tighten up.

They become smaller in diameter to restrict blood flow to that area.

So when we exercise, the arterioles to the digestive system and other organs vasoconstrict.

Okay, let's do a practise task then.

So can you complete the following table, which summarises key features of different blood vessels? You're gonna need to name the type of blood vessel in the first column, share the location, the missing gap there, structural feature, the missing gap, and the function in that missing gap.

So I've completed some of it for you.

And then the second part, I want you to explain how blood is redistributed during exercise.

Pause the video whilst you do that and come back to me when you are ready.

Okay, so yeah, the top line is of course the arteries, so they carry blood away from the heart, whereas the middle line is about the capillaries which enable gaseous exchange.

That's the function of capillaries.

And then finally we've got veins and they contain pocket valves.

That's the structural feature that helps prevent backflow of blood.

Did you manage to get all of those marks? So five marks there up for grabs.

And then into the second part of that question, maybe you said the following about redistribution of blood.

So it's called the vascular shunt mechanism and that enables blood to be redirected where it is needed most.

So during exercise, the arterioles supplying the working muscles and the surface of the skin vasodilate, and that increases blood flow and hence oxygen delivery, or enables us to cool down as well.

Whereas we vasoconstrict the blood supply to our digestive system during exercise as it's not needed there as much.

And that's why you might've been told that kind of age old saying of never swim on a full stomach, or don't swim after you've just eaten, and actually that's because your brain gets all confused.

It's trying to digest food but it's also trying to swim, and it struggles to do both at the same time.

Of course really, we're gonna go into survival mode and prioritise swimming, aren't we, over digesting food.

Okay, into the second part of today's lesson then.

So we're gonna start looking at the constituents or the makeup of blood.

Do you know what some of the different blood cells are called? Well, there's four of them, okay.

So here we've got them in a test tube and a centrifuge and separated out the different parts of the blood for us.

And we can see that red blood cells account for about 45% of the blood volume.

White blood cells account for less than 1% of the blood volume.

Platelets also account for less than 1% of the blood volume.

So what is the other nearly 55% made up of? Well, it's plasma, isn't it? Yep.

So it's the plasma that makes up the rest of that blood.

Okay, here we've got one of those blood cells.

Wonder if you know which one it is.

That's right, it's the red blood cell and the scientific term for this is an erythrocyte, but we don't need to remember that really.

Tough word to say, let alone spell.

So these red blood cells are essential for sports performers because they contain haemoglobin and it's haemoglobin that grabs hold of oxygen.

It's really good at carrying oxygen, it's like a bus for oxygen.

It grabs hold and carries it really well.

And it also carries carbon dioxide.

So the red blood cells are really important for that oxygen and carbon dioxide carrying function.

So how would your sports performance be affected if you didn't have red blood cells? What do you think? That's right, you wouldn't be able to do endurance sport, would you? You wouldn't be able to last.

You wouldn't be able to keep doing those muscular contractions for a long period of time.

What about these ones then? Can you remember what these ones were called? Well, these were the white blood cells.

Again, they've got another name, leukocytes, but don't worry about remembering or spelling that one.

But they are essential for the immune response, for fighting infections, for keeping performers healthy.

And they're generally considered those kind of growth and repair blood cells.

They fight off infections.

And then what about these ones? What were these called? Well, these were the platelets also known as thrombocytes.

Can you think what platelets do for us? That's right, they clot the blood, don't they? So they can repair wounds.

So for example in sport, if you cut yourself or grazed yourself, got an abrasion, the platelets would be sent to that site of the injury to repair the wound and clot the blood to form a scab to stop you bleeding.

And the last element then is the plasma and that makes up the majority of the blood volume, about 55%.

And it is a yellowish fluid containing mainly water but also electrolytes, so like I guess salts, proteins, hormones, and also waste products.

It's essential for blood flow.

So we want to keep our blood volume up, which is why we encourage you to stay hydrated, keep drinking, 'cause it's that water that you take in that will get digested and extracted from your body into the bloodstream.

And if you don't have much blood volume, the blood gets really thick and it doesn't flow as well.

And the problem is when we start to exercise, it's your blood plasma that starts to get lost through sweat to help regulate our body temperature, and that's why we take on more liquids if we're exercising and sweating a lot.

So let's do a quick check.

Which of the following fights infection? Is it A, the red blood cells, is it B, the white blood cells or is it C, the platelets? That's right, it's B.

The white blood cells are the ones that fight infection.

True or false then, white blood cells contain haemoglobin.

Is that true or false? That's right, it's false.

And can you tell me why? Yeah, so the haemoglobin is carried around in the red blood cells, not the white blood cells.

And when it's combined with oxygen, it's called oxyhemoglobin.

Okay, that brings us to the next task for this lesson then.

So Ahmed here is a rugby player, and I'd like you to describe the purpose of each of the four different constituents or parts to the blood and explain why are there essential to Ahmed in his rugby match.

Pause the video now whilst you do that and come back to me when you are ready.

Okay, let's take a look at what you've come up with.

So the red blood cells, well, they contain haemoglobin, don't they? And that carries oxygen.

So if Ahmed wants to last the whole match, the whole 80 minute match, then he needs a really good supply to his muscles of oxygen and he can get that from his red blood cells.

White blood cells are essential for the immune response.

So if Ahmed got injured they would be fighting infection, and they also help with the recovery after a hard game due to those micro-tears in the muscle.

Platelets clot the blood.

So if Ahmed grazed his knee, or perhaps got studded by another player and it drew blood, the platelets would rush to that area to plug the hole and prevent further blood loss.

And then lastly, we've got plasma.

So plasma ensures that blood flow and helps maintain Ahmed's body temperature during the 80 minute match by sweating, all right? So plasma is that main part of the blood that helps blood flow and also supports sweating.

How well did you do? Did you get all four keywords and the descriptions? Okay, that's it for today's lesson then.

So just to summarise, we've been looking at blood vessels, blood cells, and the vascular shunt.

I bet you didn't know that term at the beginning of this lesson.

Well, there are three types of blood vessel, the arteries which break off into arterioles and they carry blood away from the heart.

The capillaries which are just one cell thick, and that's where gaseous exchange happens at the lungs and at the muscle site.

And then we've got the veins and venules that carry blood back to the heart at lower pressure.

And because they're carrying that blood at lower pressure, they've got those pocket valves in them.

We also talked about how blood is redistributed during exercise in order to get more blood to where it's needed most.

So we talked about vasodilation, the opening up of arterioles that feed the working muscles and the skin and vasoconstriction, the narrowing of blood vessels, in particular the arterioles feeding the digestive system.

We then went on to look at the four different constituents or parts of the blood, and we reminded ourselves that red blood cells carry oxygen in the haemoglobin, white blood cells fight infection, platelets clot the blood, and plasma makes up the majority of the blood volume.

I hope you've enjoyed today's lesson, I have, and I look forward to seeing you next time.

Take care.