 And this is what we're going to talk about, one of the most important things, one of the main reasons we have kidneys is for glomerular filtration. So we're going to look at how we can measure the GFR or glomerular filtration rate, how it occurs and why it matters. So here we see just in general, remember your cardiac output should be about five liters per minute or 5,000 milliliters per minute in normal healthy person, 20 to 25 percent, usually to say 20, 21 percent of your cardiac output goes to your kidney. So that means in any given minute, if you're moving five liters of blood, then a leader of it, or you see here 1,050 milliliters of it, is going to be flowing through the kidneys. Then you'll see, I don't care about the equations, but you take that leader of blood and from it, a little over half will become renal plasma flow. And then the part that actually will be traveling through the glomerulus is going to be right at about 110 milliliters per minute. So if you have a healthy heart and healthy kidneys, you should be pumping five liters of blood, about a leader of it should reach the kidneys, and that should be turned into a glomerular filtration rate of 110. It's 125 milliliters per minute in a man, 105 in women. So that's where you get this number of 110. The GFR, as I'll show you in a little bit, it's going to be a really great indirect measurement of kidney function. And then the amount of urine, so you take that huge number, 110 milliliters every minute, that's going to lead to that 40 to 50 gallons of filtrate being produced today. And then your body will reabsorb most of that, so you only produce between one and two liters of urine. All right, so how do we get glomerular filtration rate? This is going to be very similar to how I taught you about capillaries. Sorry, my eye itches. About capillaries and how we filter out at the arterial end of a capillary and we reabsorb at the venous end. So we've covered this when we talked about capillaries in general. So you see here, it's a combination of hydrostatic pressure, the fluid pressure of fluid rushing through the glomerulus here versus the osmotic pressure sucking things back in. So the numbers don't matter to me much, but you'll see that hydrostatic pressure should be 55 millimeters of mercury. The osmotic pressure should be 30, and then you do have some capsular osmotic pressure bringing it up. But in the end, the net filtration pressure should be a positive number. It should be 10. If this number was zero or obviously negative, then you wouldn't be producing any urine. This is very important. That's a small number, right? 10 millimeters of mercury is a very small number. If you like whisper into your hand, you're probably looking at maybe 15 millimeters of mercury. So tiny pressure changes here are going to cause huge problems. So the most important thing to understand here is about blood pressure. Your kidneys are exquisitely sensitive to changes in blood pressure because they can't function without good blood pressure. If the average blood pressure in your kidneys would drop by 10 millimeters of mercury, this number would now become zero. So if you're looking at, if you take someone who's blood, the blood pressure in their kidneys is 50 millimeters of mercury, drop it to 40, their GFR would be zero. Their kidneys would not be functioning. So your kidneys are terrified of any drop in blood pressure, which is why, as you've covered in other videos, that would lead to if a drop in blood pressure or blood flow would lead to kicking in the renin, angiotensin, aldosterone system, and then also the increase of erythropoietin. So in the end, your body would prop up blood pressure, make you thirsty, increase aldosterone to reabsorb water, and increase EPO to make more red blood cells. So your body will, that will go into high alert. It's like we have to get the blood volume and blood pressure back up here at the kidneys. All right, so why does this matter so much? Why do we care? Because the GFR is the best measure of kidney function that we have. So let me give you some numbers. If you look at, if someone is just developing kidney disease, so kidney disease without a drop in GFR, they'd be at stage one. So anyone with a GFR of 90 or higher would have 90 to 100% kidney function. But then as you drop like into stage two kidney disease, the GFR would be between athletes number 60 to 89. And then if they were to say, so if someone ever tells you, my kidney function is at blank percent, what they're basically telling you is the GFR. So it translates really well. So the GFR of 60 would give you a kidney function of 60% and you're gonna drop and drop and get into stage four kidney disease. Your kidneys are failing, but not have not completely failed yet. Stage four would be a GFR of 15 to 29. So if you like, I remember my uncle at one point his kidney function was at 27%. Mainly due to the fibrosis and scarring of the blood vessels here because of chemotherapy. But that would have been a GFR right around 27 milliliters per minute instead of the normal 110. And then stage five kidney failure is going to be a GFR, glomerular filtration rate below 15. And then of course, if your kidneys aren't working, you're gonna need dialysis. So how do we measure this? There is, it's very important to know what it is, especially if you're a pharmacist or a doctor working with patients, if they have poor kidney function, it's gonna impact dosages of drug, et cetera. But a great way to measure GFR is actually use inulin. So inulin is a soluble fiber, it's a polysaccharide, but it's not reabsorbed or secreted by the kidneys. So you can actually tell what someone's GFR is really, really closely with looking at inulin. But the simplest way to do it is to use creatinine. So creatinine is one of the three key metabolic waste products I told you about, and it's the only one that's not reabsorbed. So your creatinine levels are the best way to get an estimated GFR, an estimated glomerular filtration rate, and it works pretty well. All right, so that would be how you determine the GFR. That's what the GFR is, and that's why it matters and its relationship to kidney disease. I hope this helps. Have a wonderful day. Be blessed.