This lesson is called Absorption and Transport of Nutrients in humans and is from the unit, the Human Digestive System.

Hi there, my name's Mrs. McCready and I'm here to guide you through today's lesson.

In our lesson today, we're going to describe how the digestive system and the circulatory system work together to absorb nutrients and transport them around the body.

Now we're gonna come across a number of keywords in today's lesson, which is shown on the screen now, along with their definitions.

And you can pause the video and write them down if you wish to, but I will introduce them to you as we go throughout the lesson.

In our lesson today, we're going to look in two sections.

Firstly, we're gonna look at absorption by the digestive system and then we're gonna look at transport by the circulatory system.

So if you're ready, I know I am, let's go.

So we need to understand that food has been broken down by the digestive system through lots of different processes, including mechanical and chemical processes.

And that this collection of processes is called digestion, where we're breaking down large pieces into small.

This turns insoluble food into small soluble nutrients and those soluble nutrients can then be absorbed into the blood.

So that process of digesting our food is really important.

It's an absolute essential method of getting our food from our plate into our blood.

Now most digestion, and all absorption, occurs in the small intestine.

And the small intestine is a very long and narrow tube and food moves slowly through the small intestine, because of that, and because it moves so slowly, it can be fully digested and the nutrients that are released from that process of digestion can be fully absorbed as well.

So the very fact that is long and narrow means that digestion can happen thoroughly and absorption can be complete as well.

Now blood vessels lie very close to the surface of the small intestine wall.

You can see that in the diagram there.

The small intestine and the blood vessels filled with blood are right next door to each other, and that means that particles really don't have very far to go to be absorbed into the bloodstream from the small intestines.

So the nutrients moves through the wall of the small intestines and into the blood through this very small narrow gap really between the small intestine and the blood vessel.

And this overall process is called absorption where we are absorbing nutrients from the small intestine into the blood.

So let's quickly check our understanding.

Nutrients are absorbed from the blood into the small intestines.

Is that true or false? So you should have said that this statement is false, but why? Choose an option to explain and justify your answer.

Okay, now, have you justified your answer? Did you choose option A, that nutrients are absorbed from the small intestine into the blood? Well, if you did, well done 'cause that's correct.

Now, the lining of the small intestine is highly specialised.

It's really heavily folded and all of those folds are called villi, you can see them in the picture there.

All these little finger-like protrusions sticking out from the surface of the small intestine into the space in the middle are called villi.

And these villi increase the surface area of the small intestine.

Now, surface area is a really, really important idea in biology.

It it's an important concept.

It comes up time and time again and you'll come across it in many different places within the biology curriculum.

But what is surface area? So the surface area of this cube is the total area of all of the six faces of it.

Remember, there are six faces of the cube, it's the surface of all of them.

If we compare that to a cube which has got lots of folds in it, we can see that the surface area of this folded cube is much, much greater than the surface area of just surface the simple cube.

So by adding folds into the cube, we have greatly increased the surface area of the space.

And this idea is what's happening inside the small intestine with all those villi.

Those villi, those finger-like protrusions, sticky out bits, are massively increasing the surface area of the small intestine.

Now, organisms use this idea of surface area to either increase or decrease the surface area of various different parts of their body according to need, according to their environment, what they're trying to do, how they're trying to survive, lots of different factors, which is why it comes up time again in biology.

So by adding folds into the small intestine, the villi managed to increase the surface area of the small intestine by about 40 times.

So that means that we can have a tube 40 times shorter than it would otherwise need to be if there weren't any villi.

Just imagine how much space that saves.

That's an enormous amount of space because all those folds, all those villi increase the surface area greatly.

And you can see in those diagrams a comparison of the surface area without villi, where it's very smooth compared to all those folds.

And the increase in surface area that that provides.

So surface area is really important, especially in the small intestine and increasing that surface area is essential.

Where we have less surface area, we have a smooth surface, and where we have more surface area, we've got lots of protrusions, or sticky out bits, and therefore lots of folds.

And increasing the surface area increases the rate of absorption of nutrients into the blood.

So we can see that with the lower surface area we have less absorption, whereas with the higher surface area we have more absorption, there are more arrows there, there's more surface over which absorption can take place.

And that's why increasing the surface area of the small intestine is so important because it increases the surface area, which means absorption, the rate of absorption can increase as well.

And that means we need a shorter small intestine in order to be able to absorb the same amount of nutrients.

So let's quickly check our understanding of this concept of surface area.

Which of the three shapes has the greatest surface area? What do you think, I'll give you five seconds to decide? Okay, so did you select option C? I hope so, well done if you did.

So let's see how surface area matches up with another key concept in biology diffusion.

So diffusion is the net movement of particles down a concentration gradient.

So you can see in the diagram that on the left there is an area of higher concentration.

There are more particles on the left hand side of the picture compared to the right hand side where that concentration is lower, there are fewer particles there.

So we've got a concentration gradient from higher on the left to lower on the right.

Now that means that the particles will be able to diffuse through the space.

And diffusion is the net movement, the overall movement down a concentration gradient within diffusion from an area of higher concentration to lower concentration down this concentration gradient.

So we can say that the concentration of nutrients in the small intestine is higher than the concentration of nutrients in the blood.

That establishes a concentration gradient from high in the small intestine to lower in the blood and therefore net movement of particles will be from the small intestine into the blood.

If we then increase the surface area, we will increase the rate of that diffusion because we are increasing the space over which that diffusion can take place.

So we're moving particles from high concentration to low concentration down this concentration gradient across a high surface area.

And this is what is happening with absorption in the digestive system.

So our high concentration of particles of nutrients within the small intestine and these nutrients now are things like glucose, amino acids and fatty acids.

And these are moving into the blood where there are much lower concentration of these nutrients.

These nutrients diffuse down the concentration gradient from the small intestine into the blood.

So let's just quickly check our understanding.

What I'd like you to do is complete the sentence.

Diffusion is the net movement of particles, A, up a concentration gradient B, against a concentration gradient, or C, down a concentration gradient.

What do you think, I'll give you five seconds to think? Okay, did you say C? Well done if you did.

Diffusion is the net movement of particles down a concentration gradient.

What I'd like you to do now is two tasks.

I'd firstly like you to explain why in the diagram of showing folds of villi in the small intestine, why is this adaptation so important for absorbing our food? Then I would like you to describe the process by which nutrients move from the small intestine into the blood.

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

Okay, let's see how we got on.

So with the first question showing the diagram of the folds of the villi, and I asked you to explain why this adaptation is important for absorbing our food.

So your answer might have included ideas of the villi increasing the surface area and this increases the rate of absorption.

So check your work over, make sure that you've got those two key central ideas about surface area and rate of absorption.

Then secondly, I asked you to describe the process by which nutrients move from the small intestine into the blood.

And again, your answer may have included the fact that nutrients move by the process of diffusion down a concentration gradient from a higher concentration in the small intestine to a lower concentration in the blood.

Again, check your work over.

Just make sure you've got all those key ideas about diffusion and the concentration gradient going from high to low, particles moving down that concentration gradient and well done.

Okay, our second part of our lesson today is looking at the transport by the circulatory system.

So let's just clarify what we mean by the circulatory system.

The circulatory system is the network of blood vessels which contain blood, but it also includes the heart that pumps the blood around the body.

So the circulatory system are all these tubes around our body through which blood can flow, pumped and aided by the heart.

Blood is a collection of lots of different things.

So blood is made up of plasma, which is a liquid and suspended in that liquid are red blood cells, white blood cells and platelets.

And the diagram shows, the picture there, sorry, shows red blood cells.

So blood is flowing through the circulatory system through these vessels of the circulatory system and around the body.

So once food is fully digested, the nutrients can be absorbed into the blood through the wall of the small intestine.

They can diffuse through that wall from the small intestine into the blood plasma.

And this liquid that those nutrients are being absorbed into in the blood is called plasma, that's the liquid part of the blood.

So these soluble nutrients are absorbed into the blood and dissolve in the plasma and then they can be transported around the body.

So the plasma makes up just over half of the volume of the blood and is mainly water and suspended within that, dissolved within that plasma are all the nutrients that we have flowing around our body, including sugars such as glucose, amino acids, fatty acids and glycerol and vitamins plus waste products as well, which all are getting transported around our body.

It's, you could think of the circulatory system a bit like a complex set of roads where cars are flowing, going along the roads, well the blood is a bit like the cars and the roads are a bit like the pipe work, the circulatory system itself.

So all of these nutrients and the waste products are moving around the body suspended within the plasma and moving in the blood.

So which of the following substances are dissolved in plasma? You've got options of glucose, amino acids, fibre and fatty acids, but which ones are dissolved in plasma? What do you think? I'll give you five seconds to think about it.

Okay, let's check our work.

Did you select glucose and amino acids and fatty acids? Did you spot all three of those? Well done if you did and well done if you got only one or two of them as well.

So nutrients that have been absorbed into the blood are transported around the body by the circulatory system.

And as I've said, the circulatory system is this collection of blood vessels, which allows blood to flow through them.

Now the heart is pumping this blood around the body to all the living cells within the body, and those nutrients can then diffuse out of the blood and into the cells.

And when they are in the cells, they can then be used for staining our life processes for providing us with energy, for providing us with the materials that we need to grow and also to repair ourselves.

So the nutrients, once they have been transported around the body can be absorbed into cells where they are used for energy growth and repair.

Let's quickly check our understanding.

We can see that Alex, Jacob, and Aisha have each tried to describe absorption, but whose description is correct? Now Alex says "Plasma is absorbed into the blood and used for energy and growth." Jacob says, "Diffusion moves nutrients from the circulatory system into the digestive system." and Aisha says "Nutrients are absorbed into the circulatory system and transported to living cells." But who is correct, I'll give you five seconds to decide? Okay, have you chosen Aisha? Her description is correct that nutrients are absorbed into the circulatory system and transported to living cells, well done.

So what I'd like you to do now is to use the ideas of digestion, surface area and diffusion and explain why is food digested before it is absorbed? How are the nutrient particles absorbed into the blood and what happens to the particles once they are in the blood? Now this is a complex task.

It requires a lot of detail and a lot of thought.

So take your time, make sure you use all those key ideas and all of the information that you know about the digestive system and the circulatory system to really provide a thorough and detailed answer.

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

Okay, how did you get on with that? That was a long and complex task, so I hope you did okay.

So let's see what you could have written.

So you might have included in your response that digestion breaks large insoluble food particles down into small soluble nutrients and that these nutrient particles can be absorbed through the wall of the small intestine.

The small intestine wall has a large surface area due to the villi, and those villi increase the surface area for absorption, which increases the rate of absorption.

You might have included that the particles can diffuse down a concentration gradient from the small intestine wall into the blood where it's high concentration in the small intestine and lower concentration in the blood.

And that once in the blood, those nutrient particles are then transported through the circulatory system to all the cells in the body where those cells can then use those nutrients for energy growth and repair.

Now that's a substantial response, so just check your work over, add anything that you might have missed, correct any mistakes if you've made any, and tick the bits that you've got right.

Well done, that was a hard task to do.

So just to summarise our lesson today, we've seen that particles of food are digested into small soluble nutrients such as sugars, amino acids, and fatty acids.

And that those nutrients are then small enough to be absorbed from the digestive system into the circulatory system by the process of diffusion, that in order to be diffused and in order to be absorbed, they have to pass through the lining of the small intestine through these folds in the small intestinal wall called villi, and these villi increase the surface area of the small intestine, which makes absorption much more efficient.

So thank you very much again for joining me today.

I hope you've had an enjoyable lesson and I hope to see you again soon, bye.