 Loss of proteins can occur in urein when there is damage to kidneys and this loss of protein can be very grave So how do our kidneys normally prevent this Filtration of proteins at the level of the glomerulus and hence their loss. So yes, that's the subject of this video See first step in formation of urein is filtration of the plasma at the level of the glomerulus The rate at which the plasma filters from the glomerulus into the tubules is known as glomerular filtration rate Which is normally 125 mm per minute Now you see this filtration occurs across three layers of the filtration surface So plasma is flowing into the capillaries and why are the capillaries it gets into the tubules So which are the three layers which it has to cross? First it is the endothelial layer, which is lining the capillaries Then now there is basement membrane and there is third layer also Which is the epithelial layer of the Bowman's capsule which have podocytes now these podocytes have a food Processes which encircle this capillaries So there are three layers the endothelial layer of the capillary the basement membrane and then Epithelial layer of the Bowman's capsule or what we call as food processes of podocytes Now see the plasma has various substances like cells are there there are ions that is the electrolytes Then there are organic molecules So when this plasma filters through these layers to all these molecules also filtered along with plasma Or there is some selective filtration of certain substances and others are not filtered And if it is so then how it is determined with substances with filter Well, it is defined by the characteristics of these three layers So first thing is that these layers are negatively charged all the layers are negatively charged The endothelial layer has glycocalyx then this basement membrane which is nothing but collagen and certain glycoproteins So these glycoproteins are actually negatively charged then the food processes of the podocytes They also have a negatively charged proteins in the spaces between these food processes. What is known as slit diaphragms So one thing which determines that what substances will cross these layers is the charge of the substance and The second thing is size of the substance See these endothelial cells in the capillary There is certain space between them and the space is quite large what we call as fenestrations, right? So lot of plasma can filter this space between endothelial cells is around 15 nanometers Then these food processes they also have certain a space between them that is around 25 nanometers So you may think that substances less than 25 nanometer in size will filter No, it doesn't happen like that because the filtered fluid and the substances which are filtered have to pass through a Trabacular network which is present in the basement membrane. So there is a network of collagen and glycoproteins These form some tortuous channels and through these channels only the substances has to pass So the maximum size of the substance which can pass is around 8 nanometers only Okay, so two things are there one is the size of the substance and the second is the charge of the substance Now let's try to understand this by means of this particular graph that which substances will be filtered more and the substances will be Filterless and which may be filtered none at all Okay, so in this graph x-axis is showing the effective molecular diameter of the substance Which is in nanometers and the y-axis is showing relative Filterability of the substance which is defined with respect to water So if it is like 0.75 that means 75% of the substance is only Getting filtered or we can understand it and other terms also Say suppose a substance is having a plasma concentration of 100 milligram per 100 ml and After filtration if the concentration in the tubules is also 100 milligram per 100 ml that means it is freely filtered Nothing is being retained in the plasma However, if the concentration in the tubules is say suppose 10 milligram per 100 ml then only 10% of it is getting filtered Right, so it is here. It will be 0.1 Okay, so here y-axis is showing relative filterability Now first let's see how neutral substances that is uncharged substances will be filtered So here this graph is showing their filterability You see when the size is less than 3 nanometer the diameter of the substance is less than 3 nanometer Then the substance is freely filtered. You see the relative filterability is 1 but as the size keeps on increasing from 3 nanometer to further the Filterability of the substances decreasing isn't it? So at around 7 nanometer or 8 nanometer none of the substance is getting filtered Okay, now let's see the charge substance So here this graph is showing that how the filterability will be for a negatively charged substance or anionic substance You see obviously it is much less than that of the neutral substance. Is it it for the same size? You see filterability is quite less isn't it? Why is this? Yeah, as already told that there are two things which are important size of the substance and charge of the substance So since the membrane is negatively charged it is repelling this negatively charged substance and hence causing its decreased filtration So you see the maximum size of the substance which is getting filtered is 6 nanometers only isn't it? Okay for the cationic substance how will it be? Yes, of course they will be filtered more compared to that of the neutral substances So in summary from this we can deduce that any neutral substance which is less than 3 nanometer in size It will be freely filtered isn't it? Then as their size increases from 4 nanometer to 8 nanometer their filtration will decrease Then for anionic substances any substance greater than 6 nanometer will not be filtered at all and Thus overall we can say that freely filtered substances will be water Electrolytes and some organic substances which are a small and non-charged like glucose Okay, so let's solve one question before we end See here is a list of substances and now can you tell me that which substances will be freely filtered which substances will be Partially filtered and which substances will not be filtered at all Yeah, you see that These electrolytes sodium potassium they are very small they will be freely filtered Then urea, glucose they are also freely filtered they are small they are not charged But if we say what about albumin? See size of the albumin is around 7 nanometers, but it is negatively charged and we have said before that Any anionic substance greater than 6 nanometer is not filtered So here you see albumin is a protein which is not getting filtered Because the membrane is negatively charged What about calcium? Calcium even though it is an electrolyte it is partly filtered why? Because in the plasma part of it is bound to plasma protein So any substance which is bound to plasma proteins also will not filter On the other hand fatty acids they are almost completely bound to plasma protein So they are not filtered at all Yes, so that's the concept by which we can know the filterability of a substance And there is a disease known as minimal change your disease in which this negative charge of the membrane is gone So you see if the negative charge is gone what will happen? The proteins will start appearing in the urein Well, thanks for watching the video if you liked it to press the like button share the video with others And don't forget to subscribe to the channel physiology open. Thank you