armanda hugan biology and Medicine videos please make sure to subscribe join the foring group for the latest videos please visit Facebook arand hugan please like and here you can also ask questions answer questions and post some interesting things including your artworks and you can also change the quality settings to the highest one of better graphics in this video we're going to continue on from where we last left off urine production and remember that there are three major Realo processes filtration reabsorption secretion and the fourth one we can say is excretion let's begin looking at urine production by firstly looking at filtration GL glomular filtration which is the first step in urine production so plasma volume entering the afron arterial is about 100% 20% of this is filtered into the nefron leaving 80% still in the arterial in the bloodstream this 20% Which have just been filtered more than 19% % of it will actually be reabsorbed by the blood and so more than 99% of the plasma return to systemic circulation from entering the afron arterial meaning that we have less than 1% of the volume of the plasma actually excreted I hope this makes sense an important terminology to note is filtration fraction filtration fraction is the amount of plasma filtered from the gloma into the nefron and this is 20% % now let's look at how the substances actually get re uh get filtered from the GLA into the nephron so here I'm drawing the afrine arterial and uh the Efren arterial the Ephron notal coming in and the Ephron notal going out of the Bowman's capsule here are the glom capillaries and this is the Bow's capsule we have special cells surrounding this area known as mesing cells mesing cells contain actin which perform contraction and so have important Ro have an important role in altering blood flow and then we have these other cells surrounding the arterials known as granular cells and if you remember they are the cells that secrete the hormone renin and then we have the thick ascending limb which go which passes in close contact to the head of the nefron and this is because they contain special cells known as macular Densel cells which are chema receptors uh which which help balance um ion which which help balance ion levels of sodium and chloride passing through and finally the most important thing we should know is that there are poyes in the gloma glomus poyes are important in the filtration process which is the first step in urine production poyes have many feet likee projections let's have a look at how substances get filtered and how poyes are important in this process by taking a cross-section of this GL capillary so here we have the actual capillary and here we have missing cells poyes surround the capillaries with its many feet likee projections like so remember inside the capillar we have ions we have red blood cells solutes essentially let's take a closer look at this membrane these membranes and how substances get filtered just a just a quick look the first membrane is the capillaries endothelial cells which are fenestrated which means that they have gaps allowing for solutes to move from the capillary into the nefron the second layer we have the basement membrane where solutes can still easily pass through the outer uh layer we have poyes feet like project feet like projections of poyes foot of the potto sites and they are spaced out or they can be very close together and these and they will have also gaps between them allowing for filtration the endothelial cell the basement membrane and the poite make up the group of membranes known as the filtration membrane now the filtration membrane being that where there is a gap is they they they make a filtration SLP which means that substance can actually get filtered from the capillary into the nefron the filtration membrane controls what type of substances moves into the nefron they actually do not allow big big molecules to move through and they do not also allow big negatively charged molecules to pass through why is this well let's have a look again at the here we have the glomular capillary and we have substances within this GL capillary we have negatively charged proteins we have negatively charged ion such as chloride we have positively charged ions such as sodium and also we have a negatively charged protein such as albun now the poyes and the base of membrane are actually overall negatively charged due to proteins and carbohydrates on them known as proteoglycans so because of proteoglycans poyes and basement membranes are overall negatively charged what does does this mean it means that positively charged molecules are absorbed more readily and easily than negatively charged molecules for example albumin which can actually pass through because of its uh good size doesn't pass through because it is negatively charged and so negative repels negative sodium can easily pass through because it is positively charged and so it's attracted chloride can actually pass through because it is very small and even though it's negatively charged it can still pass through however the these big big negatively charged proteins they will never pass through because for one they are too big to pass through and second they are negatively charged and so repel the negativity of the pyes and the basement membrane basically the glom capillary okay so we know that substances can move from the gome capillary into the nephron because of these filtration slits but what causes them to move from the glomus into the nefron well pressure causes them to move from the glos into the nefron so let's look at filtration pressure and how it causes these substances to move from the glus into the nefron sorry I'm saying glomus and Nephron like 20 times so here we have the head of the Nephron the Bowman's capsule and the glos capillary aial going in and AAL going out let's first of all look at the pressures that favor filtration which is outward movement out of the glomus and this pressure which favors filtration is known as the glom hydr hydrostatic pressure abbreviated P for pressure GH and this is about 60 um millim Mercury and then we have pressures that opposes filtration and this is inward so substan is moving back into the glomus and these pressures are the Bowman Bowman's capsule pressure abbrev p for pressure G BC and this is about 16 mm Mercury and then we have another one which opposes filtration which is glomular colloid osmotic pressure p for pressure GCO and this is about 34 mm Mercury so what does this all mean well the net filtration pressure NFP would be the outward pressure oh meaning the movement out of the glomus minus the inward pressure the movement into the glomus so to calculate the net filtration pressure it would be pressure of uh hydr hydr gloma hydrostatic pressure minus the Bowman's capsule pressure minus the glomular colloid osmotic pressure so it's 60 minus uh 16 - 34 and this gives us 10 mm Mercury positive 10 mm mercury in the right in the filtration Direction so it means that the net filtration would be 10 mm Mercury and also remember that this pressure and Direction fa makes it favor filtration next concept to understand is what's called GFR the glal filtration rate GFR is the volume of fluid that filters into the Bowman's capsule per unit of time and this is on average for a human 100 125 Ms per minute or 180 l a day so this is just the amount filtered but remember that less than 1% of the volume is actually excreted so to find GFR um we have to find KF and times it by the net filtration rate we know what the net filtration rate is it's about 10 mm Mercury right the KF is a glome capillar filtration coefficient and this is calculated or found by measuring the surface area of the G capillary available for filtration and also its permeability I'm not going to really talk about the KF but this is just important to know how to um how to calculate the glal filtration rate so why is it important to know that how to calculate GFR well if we know that KF times net filtration rate equals gfl we know that if we alter the net filtration rate this will also alter the Glo filtration rate and so the amount of fluid that gets filtered into the Bowman's capsules and so this will alter the average glal filtration rate if the glome filate filtration rate is increased or decreased this can tell us um how how the kidney is functioning if it's low it means that the kidney there's some problem with the kidney if it's high there's also some problem with the kidney so it's it's a good indication of kidney function so we can alter NFR to alter GFR and so NFR if you remember the net filtration rate is equal to the GL glome hydrostatic pressure minus the bonus capsule pressure minus the glome colid osmotic pressure so we can alter net filtration rate by specifically altering the glome hydrostatic pressure which is the blood pressure entering the glome the glomus inside the Bowman's capsule so if we alter the glome hydro static pressure we will alter the net filtration rate which will in turn alter the glomular filtration rate and therefore the amount of fluid which gets filtered from the capillary into the Bowman's capsule I hope this all makes sense it's important to know so essentially if here is the nefron the head of the nefron the AF Aon the Bowman's capsule here is the glal hydronic pressure PGH so if we alter this we can alter the NFR and so the GFR now the gloma hydratic pressure can be altered by changing the resistant in the afren or the eant arterial what do I mean by this so let's just go back to another simple diagram of the nefron and the blood blood uh capillary coming in if there's no resistant on the afron arterial so it's just normal this would mean that the gloma hydrostatic pressure is also normal which is about 60 mm Mercury and therefore if the glome glomular hydrostatic pressure is normal this would mean that GFR would be normal however if there's an increased resistant on the afron arterial coming into the Bowman's capsule this would mean that there would be a decrease in glomular hydrostatic pressure and therefore a decrease in the glom filtration rate now what if the eant arterial is just normal but there is an increased resistance on the eant arterial the arterial coming out of the Bowman capsule if there was resistance in the eff arterial this would mean that we would have an increased in hydrostatic pre pressure within the glomus and therefore we would have an increased um filtration rate glome filtration rate so now let me ask what would happen if instead in of having a um increased resistance on the AFR arterial we have a decreased resistance in the afron arterial so the afference arterial coming into the Bowman capsule is dilated what would this mean well this would mean that more blood would be able to rush inside and therefore this would increase the glomular um hydrostatic pressure and therefore the glomular filtration rate and from all these diagrams we can see that when what ever happens to the glal hydrostatic pressure will be the same for the glal filtration rate so if the hydrostatic pressure increases the GFR also increases if the hydrostatic pressure decreases the GFR also decreases so that concludes this video on glomular filtration and this video only looked at filtration everything to do with filtration the first step in urine production in the next video we'll look at reabsorption how the filtrate gets reabsorbed back into the blood with and that's the second step of urine production thank you