Hi everybody and welcome back. Today we're going to be looking at ultrafiltration in the kidney. If you are new here don't forget to like and subscribe because every week I will be posting a new video on a different topic. So let's get into it.
Ultrafiltration. Ultrafiltration is essentially our body's way of removing both useful and waste products and this might sound counterproductive like Why would you want to take out the useful stuff? Essentially, we take the useful stuff out because we have to regulate the useful stuff.
We have to regulate if we have too much of it or too little. And of course, in terms of wastes, we need to regulate our wastes. We need to remove as much as possible. And so in ultrafiltration, we actually do both at the same time. Now it's important for us to identify the location of ultrafiltration before we go any further so that we know exactly where this is all taking place.
And ultrafiltration specifically occurs in this structure over here at the beginning of our nephron, which is called the Melpigean body. It is made up of two components. One is the glomerulus, which is this capillary network that we see over here. And the other is this Bowman's capsule. Together, they filter out all of your blood and they take out useful and waste products and they create a substance called filtrate, which is a liquid.
That liquid then makes its way down the whole length of the nephron. And as we'll learn in some follow-up videos, different sections of this nephron will then absorb or exchange useful and waste products as we go along. Now to have a better understanding of ultrafiltration, we're going to have to look at the structure of the malpighium body and how it enables it to do its function.
Now we've zoomed in on the malpighium body structure, we need to break it down into its two main components. And we're going to look at exactly how these components allow ultrafiltration to occur as best as possible and how we maintain this filtration constantly. So the first major component of the malpighium body is the glomerulus.
And the glomerulus is made up of of this network, as we can see here, of blood capillaries that increase the surface area and essentially allow a large amount of blood to pass through and to be filtered. A component of the glomerulus is, of course, the arterioles that flow into the glomerulus. Now, the arteriole that goes into the glomerulus is called the afferent.
Afferent means in. And the part of the arteriole that leaves is called the afferent. efferent, the exiting. Now you will notice that they have been drawn at different sizes and this is really important because the sizes of the tubes of the blood vessels determine the blood pressure that's moving through the glomerulus and we always want to keep a high blood pressure in order to maintain something called hydrostatic pressure, which is essentially the pressure that is exerted on the walls of the blood vessels via the liquid moving through them. In other words, we always really want a high pressure of blood flowing through the malfeasance body so we can filter out as much as possible.
And so in order to do that, we have an afferent arteriole that is actually quite short and wide. And we can see that here that the opening of the afferent arteriole is wide. And you can see even over here, the diameter is much wider. If you look at the efferent, on the other hand, you will notice it's much more narrower across its diameter and smaller.
And the reason for that is we are trying to take a lot of liquid and we're going to try and squeeze it through a smaller space. And this squeezing action allows us to maintain blood pressure. And it also facilitates enforcing particles that we want to get out of the blood into the Bowman's capsule and then into the filtrate.
Now that then brings me to, of course, Bowman's capsule. This is the capsule that sits around the glomerulus. And this is where eventually our filtrate is going to collect. And so getting back to our afferent and efferent arterioles, these blood vessels where the blood comes in in the afferent, they're going to squeeze the blood from a large area, squeeze it down into a smaller area. And in doing so, it forces any of the particles that are...
being needed to remove down the blood, it gets forced into Bowman's capsule, and then Bowman's capsule does the final filtering. Now, what does the Malfugium body have that assists it along with the afferent and efferent arterioles infiltration? Well, we're going to look at a closer picture of the glomerulus and Bowman's capsule. So you can see once products go into the glomerulus, how do they actually move through the wall of the glomerulus and then into Bowman's capsule? Ultimately, what does ultrafiltration look like if we get really close to the tissues?
So now what we've done in this photograph here is we've zoomed up really, really, really close to the edge of the glomerulus as well as the Bowman's capsule. So as you can see here, it says endothelium. This endothelium represents the thin lining of the glomerulus, the thin, thin capillary lining. The green layer on the other side here, it says a podocyte.
Now podocytes are specialized cells that are in the Bowman's capsule. And so what you have is you actually have two filtration layers. So first of all, the endothelium over here in the pink, that is going to be where our capillaries are. So as you can see, here's our blood.
And remember, our blood is filled with substances that are useful, but also wastes. And we're trying to filter those out, hence the name ultrafiltration. So what happens is because the blood is coming at such a high pressure, Because of it being transported from the afferent to the efferent arteriole, squeezing, remember, try to squeeze as much through as possible, what you find is a sieving action. Now, if you think of what a sieve is, it's where you take flour or sugar and you basically pass it through a fine mesh to get out all the big particles and all the smaller particles can move through.
And that's exactly how ultrafiltration works. The only difference is that we're actually going to sieve. the substance or the blood twice.
And if you are lucky enough to make it through both spaces, then you become a part of what we call the filtrate. So essentially, this is how the movement of our blood goes. It enters into the glomerulus.
And the first thing it needs to do is it must make its way through what we call a pore. This is a pore that is in the walls of the endothelium, these small little holes. And if you are a part of...
that is small enough to move through that space, then you've luckily made it through the first layer. The second layer you have to make it through, and you have to be small enough, is these podocyte slits. This is a part of the Bowman's capsule. If you are lucky enough to make it through both of these holes and both of these spaces, you are now part of the filtrate.
A good way to think of what exactly is the filtrate is to imagine it being a... somewhat clear liquid that has a lot of useful substances in it, but it also has a lot of wastes in it. It actually essentially is blood without the red blood cells in it.
And we're going to now look at what substances can actually make it through the filtration and what can't make it through the filtration. So let's look at the substances that are able to make it through. So the following substances are going to be able to make it through our filtrate. They are things like urea.
salts, glucose, and amino acids. They are small enough to fit through both the pores in the endothelium and the podocytes. They can make it through both filtration points, hence the name ultrafiltration, and they then make it into the filtrate.
Now, if you look at that list, there are some useful substances such as glucose and amino acids. There is also wastes like urea and salts. To some degree, salt is also a useful product, but we're going to learn in another video how do we actually regulate salt.
Now, all the substances that remain in the blood are too big to leave, and they can't actually fit through these small spaces that have been provided by the endothelium and the podocytes. And these are substances like red blood cells, platelets, and large blood plasma proteins. They're basically really big.
clumpy globular proteins that can't fit through these spaces. And that's a good thing because you should never have red blood cells in your filtrate. If you do, that means you'll have eventually blood in your urine. It's at this point I want to make it very clear also that filtrate is not urine yet. It only changes its name right at the very end of the process when we're all the way at the distal convoluted tubule.
So to finally summarize, essentially ultrafiltration is when the blood moves at a high pressure into the glomerulus. We select out specific substances that are small enough to move through the endothelium pores and the podocytes of Bowman's capsule. And those substances are either wastes or useful substances, and they become a part of the filtrate. All the larger substances like red blood cells and platelets. cannot enter into the filtrate because they're too big, they cannot go through the filtration process, and they remain in the blood and they leave via the efferent arteriole.
As always, I like to finish off our lessons doing a terminology recap in order to make sure that we're very familiar with the words that we have learned because learning these words is what enable us to answer these questions as quickly and easily as possible in exams. So first we looked at the Malpighian body, which was a structure where filtration occurs and the Malpighian body is made up of two components. The first component is the glomerulus, which is a dense network of capillaries that intertwine with one another, and it is there to increase the surface area so that filtration occurs faster. And it has an afferent and efferent arteriole, which I'll get to now in our terminology list. Essentially, that is what brings our blood into the glomerulus and then what leaves out of the glomerulus.
We then have Bowman's capsule, which is the structure that the glomerulus sits inside of, and this is the final component that... we need for ultrafiltration. Blood must move through the glomerulus, then through Bowman's capsule.
And once it's done so, then it has been ultrafiltrated. Now, earlier I spoke about these arterioles with the glomerulus, and that's the afferent arteriole, which is the artery that goes into the glomerulus. And the efferent arteriole is the arteriole that goes out of the glomerulus.
Now, why are they so important, these two arterioles? Well, their widths are different. The afferent arteriole is wider than the efferent. Why is this important? Because it maintains hydrostatic pressure.
Essentially, hydrostatic pressure is the forces exerted on the walls of the blood vessels to maintain your blood pressure. Blood pressure is really important in maintaining your overall physical health and cardiovascular health. And to do that, we have to try and squeeze blood from the afferent arteriole, which is much wider if we did a cross-section through it, compared to the efferent, which is much more narrow.
And the difference in the opening width improves the pressure. Then we spoke about podocytes. And podocytes are these unique cells that we find lining Bowman's capsule, and they assist in ultrafiltration. in that they have something called a slit within them. It's basically a thin opening, which allows only certain substances to move through.
And so if you are lucky enough to move through both the glomerulus and Bowman's capsules, podocytes, you now become a part of the liquid called filtrate. Filtrate is the liquid that we produce after ultrafiltration. It's important to note that it is not urine.
It will only become urine at a later stage. This filtrate is also going to be looked at at a later video as well. And I'll unpack exactly what do we do with it after an ultrafiltration. And that's it for today, everybody. I hope that this has been a helpful video.
And if you liked it, make sure to like the video, subscribe. I will keep you updated with as many exam and study tips as possible. But I'll see you all again very soon. Bye.