welcome back welcome back welcome back to science all right we're going to start the first part of urine formation so this is in chapter 20 section three this is where it starts to get deep until now we've just kind of been talking about the structures this is the how it works so urine exactly what is it so this is going to be the um the products of the nephritis the nephrons filtrate so this is the waste but most of the stuff that is filtered out at the nephron is actually reabsorbed and so we've got to look at kind of the process of your information so that's going to include the glomerular filtration tubular reabsorption and tubular secretion so and the glomerular filtration it's going to be performed by specialized glomerular capillaries water and small amounts are filtered and then the filtered fluid are going to enter the renal tubules so at this point you would think like hey it's filtered it out it's done no matter of fact a lot of what is filtered out it's going to come right back so the transfer of the filter substances from the renal tubules to the perituber capillaries which is the secondary so we have the afferent enter into the the glomerulus and we have efferent leaving but we're not done we're eventually going to that's still arterial arterial now we're going to get to the point of being in that capillary bed and there's going to be a relationship with the distal tubule of the capillary and it sending stuff back and forth Not Just One Direction so tubular secretion is the transfer of certain substance from the peritubular capillary to the renal tubules and it's going to add waste and excess substances to form eventually urine so we have afferents glomerulus efferent protubular capillaries and take a look some stuff is still diffusing into the perituba capillaries some stuff is diffusing out and so there's a few different mechanisms not just of using them but things are going to be leaving this tubule and things are going to be going into the tubule so let's look at glomeria the filtration this is the first step of urine formation this is what we're going to have as cleansing the blood and this is going to be based on just by size for the most part so substances removed from the blood into the glomerulus and into the glomerular capsule water and small dissolved molecules and ions that can be filtered larger things can't so those large plasma proteins they're staying in the blood this is good and we don't want to filter those out anyway so the glomerular capillaries are much more permeable than like a capital capillary somewhere else in the body because of thin stray thin stray from the same vein as the concept of finstration but these are going to be the tiny openings that are going to be in the wall the glomerular filtrate is formed as substances filter from the glomerulus into the glomerular capsule the filtrate has about the same composition as the tissue fluid around it and so it's not affecting it Downstream we're going to see some changes so here's the afferent flowing through we can see it's larger uh what's going to point out and we see the efferent which is going to be smaller and you can see the protocytes that are going to be here in the glomerulus this is going to be the glomerular space where we're going to have the proximal collecting duct and you can look and if you zoom up on this section right here you can see all those perforations in it these are the fin stray that are going to allow things to move out of that all right so filtration pressure blood pressure seems to affect everything so the main force that filters substances through the glomerular capsule wall is the hydrostatic pressure of the blood of the glomerulus so if you have high blood pressure this is going to affect your filtration if you have low blood pressure also so the afferent arterial has larger diameter than efferent and other parts of the body the resistance of the efferent arterial includes increases the blood pressure of the glomerulus so if this is really really constricted this is going to have high pressure in this area causing movement out so the net filtration pressure is going to be equal to the force favoring filtration and the force opposing filtration so things that are going to favor filtration the glomerular capillaries hydrostatic pressure so this is going to be the hydrostatic pressure in here of the fluid the opposing it's going to be the colloid pressure which is going to colloid osmotic pressure which was referring to the things that are within that are having a relationship with the osmotic concentration as things are going to move in or out based on the collates the things that are there so this is going to develop in the capsular hydrostatic pressure as long as the net filtration pressure and the glomerulus of positive filtration will occur so here we have the glomerular hydrostatic pressure it's going to have a bulk moving out the plasma colloid pressure meaning that there's more solutes on this side than this side so you're going to have a net movement in you're going to have the capsule hydrostatic pressure and notice that whenever you do the math of all those adding them all up you're going to find that there's a net filtration pressure that's going to be filtering out so as long as the numbers are positive in comparison we will have net filtration all right the glomerular filtration rate kidneys receive about 25 percent of the cardiac output 20 percent of your blood is filtered by the glomerular the capillaries so to put it into numbers the average don't has a glomerular filtration rate of about 125 milliliters a minute which equals about 180 liters a day so your blood plasma is filtered about 60 times a day so only a small amount of that is actually getting to the point of being called urine so the glomerular filtration rate is directly proportional to the net filtration pressure so that anything that changes the net filtration pressure will change the glomerular filtration rate which is going to be the glomerular capsular hydrostatic pressure or the glomerular colloid osmotic pressure things that are affecting that flow rate changes in diameter of the afferent or efferent arterial so this is amount that's actually filtered this is about the amount of byproducts that you produce a day everything from 0.6 liters to 2.5 liters of urine a day something like that that's a lot compared to the 180 that we have and you may think like well for filtrating so much why doesn't that just flow out that's a great question that is like the heart of where we're headed so thank you for asking that question all right so Auto regulation keeps the glomerular filtration rate relatively constant so an increase at the systemic blood pressure causes vasoconstriction of the afferent arterial this is going to reduce the amount of blood that's actually going to the glomerulus so that's going to decrease the glomerular filtration rate and that's going to maintain kidney function so this is something that we're doing as increase in blood the systemic blood pressure is going to cause vasodilation all right excuse me basic constriction all right the juxt glomerular apparatus and the tubular feedback if you have an increased glomerular filtration rate this increases the amount of filtrate in the renal tubules once again the tubules are the things it's leading away from that the loop a descending loop of anything Loop of handling and eventually you get to the point of the distal tubule so an excess salt reaches the macula densa and if you remember the macula denza is going to be you have the glomerulus afferent efferent and you have that collecting loop as it is coming up as the ascending collecting Loop right as it pretty much touches where that glomerulus is it's going to have a relationship there so an excess salt reaches the immacula denza and the distal tubule of the juxtagomerular apparatus the afferent arterials are vasoconstricted so this is the afferent here so it's going to constrict as a result of this since you have less blood flow flowing to your glomerulus you're going to have the glomerular filtration rate is decreased toward the normal range as a result of excess amounts of sodium so certain conditions may increase or decrease the glomerular filtration rate in order to maintain homeostasis such as when the glomerular filtration rate increases in response to excess body fluids so hormone control now we're getting into the cardiac hormones so we have the anti atrial naturetic peptide ANP and the ventricular naturetic peptide BNP in response to increase blood volume and pressure so increased excretion of sodium and water as a result so sympathetic nervous system so remember we have rest and digest of being the parasympathetic and we're going to have the sympathetic which is going to be tied to the fight or flight sympathetic is going to exert neural control over the glomerular filtration rate sympathetic changes sympathetic responses to changes in the systemic blood pressure also affect the kidneys so when the blood pressure or blood volume decreases sympathetic stimulation causes the afferent and efferent arterials to constrict simultaneously when both of those are constricting is just going to have less of it it's not going to have more urine production or less this is going to maintain it because you're closing both hormonal control of the Angiotensin aldosterone system all right so this is also called Angiotensin system activation by decreased blood pressure you're going to have the sympathetic stimulation or the macula densa that's going to be involved so a decrease in the amount of sodium this is going to cause secretion of renin renin and renin renin so as you have decreased salt we now have renin produced renin is going to convert something called angiotensinogen to Angiotensin one Angiotensin 1 is going to convert to Angiotensin II by the Angiotensin converting enzyme but Angiotensin II causes vasoconstriction of the afferent and efferent arterials and secretion of antidiuretic hormone and lost all and aldosterone as a result your body is going to become thirsty and your body is going to retain water and sodium and it's also going to increase blood pressure so this anti-diuretic hormone is going to increase blood pressure and you can think like the opposite diuretics are going to decrease blood pressure so here we have blood flow in decrease glomerular filtration rate basal constriction of the afferent arterial decreases the net filtration and the glomerular infiltration rate when we have vasoconstriction of the efferents this is going to cause an increase in that filtration because the same blood flow is flowing in nowhere to go this is decreased capacity here so more is going to exit you're going to have increased glomerular filtration rate where if you decrease the blood flow in you're going to have decreased glomerular filtration rate all right if you're having a decrease of the afferent and efferent you have basal constriction of both you're going to have the net filtration pressure decrease but not as much as it would respond to the affair and arterial construction alone all right let's say that you make this really wide this is going to cause an increase so you're going to have more blood flow here just based on Flow the vasodilation to the afferent arterial increases the net filtration pressure therefore you're going to have more product produced so notice the size of the arrows are going to change based on where you're causing the constrictions of the afferent or efferent or both or the evasive construct vasodilation of the afferent all right so Angiotensin angiotensinogen is produced by the liver the liver is going to cause angiotensinogen to be converted by renin to Angiotensin one Angiotensin 1 is then going to have Angiotensin converting enzyme Ace to angiotensin two angiotensin two is going to cause vasoconstriction increased aldosterone secretion increased ADH secretion increased thirst all right so tubular reabsorption and this is the movement of most useful substances from the renal tubules back into the blood um of the perituberal capillaries so most tubular reabsorption about 70 occurs in the proximal tubule which is lined by with a microvilli different parts of the renal tubule reabsorb specific substances that's why you're seeing some that are occurring in one spot and then some that are going to occur at another swine so substances are transported through diffusion passive transport and even osmosis so diffusion is going from a high to a low this is going to be a type of passive transport and you're going to see a lot of lipid soluble substances that are going to move here those nonpolars those hydrocarbon stuff move here as well as the aldosterones our cholesterol derivatives passive transport is going to do things like ion channels these are oftentimes polar or structures that are built just for a certain kind of transport of material that's in that vessel and then we have osmosis which is going to take advantage of the colloid osmotic pressure where it's going to have the amount of solutes on one side will draw water from the lower solid side towards the higher solid side once again this is a passive process but it's going to utilize solutes now active transport is going to use energy that's just what it does and so this is going to have a certain cost to it these are going to move things against its concentration gradient limited transport capacity due to the number of carriers so at a certain point you'll be saturated you have like the transport maximum that you can actually move at one time this is called the renal plasma threshold that's how much like with active transport the max that you can move at any time anything beyond that amount is going to spill over into the urine it's not going to be reabsorbed and so you're going to have substances that are reabsorbed by active transport things like glucose amino acids lactic acid citric acid phosphate sulfate calcium potassium and sodium ions here we have the glomerular filtration and we see that we're not actually done yet we have reabsorption and we also have the tubular secretion that's occurred and notice that we can continually have this and we have other places where we have reabsorption and tubular secretion I see the peritubular capillaries as it's moving away all right so nephritic syndrome this is a set of symptoms that occur in people with a renal disease summary disorders cause increased permeability of the glomerular membranes which allow plasma proteins to enter the urine loss of plasma proteins into urine causes widespread edema and causes the likelihood of infection because you have diffusion out because so you don't have the collateral osmotic pressure that you would have had decreased concentration of our plasma proteins decreases the osmotic pressure leading to edema ascites and feudal accumulation in several body cavities so the demon and normal fluid accumulation leads to a decrease in blood volume and blood pressure these events lead to activation of the renin Angiotensin system and ADH and aldosterone secretion this the kidneys will conserve the amount of sodium to use it and the purpose of glycoloid osmotic pressure so it's going to draw things from one side together as well as water which restores blood volume and makes the edema actually worse all right so sodium and water reabsorption about 70 percent of sodium ions are reabsorbed into the proximal tubule by active transport once again this uses energy sodium active transport provides energy and method for reabsorption of many nutrients like glucose amino acids ions vitamins and water we work so hard to break down to get the point of having the glucose and amino acids and these electrolytes of these ions that we want to maintain these as much as possible the sodium potassium pump creates a gradient that provides for reabsorption by secondary active transport sodium is going to diffuse down the concentration gradient other substances are co-transported by carrier proteins with epithelial cells of renal tubules glucose and negatively charged ions like chlorine and bicarbonate are reabsorbed by this method all right process continues throughout the renal tubules and 97 to 99 of the sodium and water are reabsorbed before excretion of urine even though you have water in your urine that's mostly what it is we have a lot of it at this actually maintained so ADH increases water reabsorption and aldosterone stimulates sodium reabsorption this is a breakdown of the amount filtered per day about 180 liters of water and about 630 grams of sodium the percentage reabsorbed per day 99 and also 99.5 respectfully the amount of spreader per day is 1.8 liters and 3.2 grams of sodium per day so here we have the glomerular filtrate the afferent going into the glomerulus and then you have the efferent leading away from and you can see sodium the sodium ions are going to be reabsorbed by active transport but now that you have the sodium that's been reabsorbed this is going to cause other things to respond osmotically so bicarbonate ion reabsorbs is linked to the sodium reabsorption so since you have a larger concentration of this you're going to be able to pull across because you've created a grading all solutes are reabsorbed as as these solids are reabsorbed water moves from the proximal tubule to the capillary biosmosis once again we have created an osmotic gradient by adding a lot of solutes here since we've added a lot of solutes water is chasing the solute going into this peritubular capillary on the efferent side and so we're able to pull the water out of this collecting do it dot preventing water from leaving this let's say that you're very very hydrated you also have chlorine of reabsorption is linked to the active reabsorption of sodium ions and it is also driven by the concentration graded of chloride that results from water reabsorption so what all this means let's say that you have excessive amounts of water in your diet let's say you drink a gallon and a half that day so you're going to be filtering out a lot of water and this is going to be pretty dilute and so since this is diluted you're not going to have as much osmosis that's going to be driving it to the other side because you don't have as many solids because they're more diffuse here um and so since you have that relationship you have more water that will be lost and sent to the collecting duct all right so tubular secretion this is the reverse of tubular reabsorption the movement of substances from the plasma or the peritubular capillaries into a fluid of the renal capillaries substances are derived from about 80 percent of plasma is not filtered by the glomerulin essentially waste and large molecules active transport molecules function in the tubular secretion but work in opposite direction of as the tubular reabsorption substances secreted into the forming urine you have drugs an ion such as potassium and hydrogen the secretion of hydrogen ions is important in regulating the pH of the body because you literally you can get rid of that low ph and which would bring your pH to being more neutral to basic and remember that our body is going to be about seven three seven point three five um typically in our blood and so we're wanting to be a little bit basic on that scale potassium ions is secreted as the sodium ions are reabsorbed and the distal tubules and so here you have potassium and the perituba capillary we have the sodium and we can see some sodium still leaving and we have potassium that is going to diffuse in here and we have some of that sodium and potassium that will leave we have a lot of it that's reabsorbed all right guys that's going to end it for the subsection I'll see you soon