Chapter 25 Urinary System - A&P II

Distinguish between cortical nephrons and juxtamedullary nephrons in terms of both location and significance.

2 classes of nephrons, cortical and juxtamedullay Cortical nephrons are going to be primarily located in the kidney. The are located about 2/3 of the way into the cortex. The loops of henle is primarily in the cortex. You have about 85% of cortical nephrons. Juxtamedullary nephrons are going to be very close to the medulla. The loop of henle is going to dip right into the medulla, this is important because it affects osmolality vs osmalarity. You only have about 15% juxtamedullary nephrons. And then you have peritubular capillaries that are blood capillaries that wrap around the whole nephron. So all the tubules of the nephron get wrapped around these capillaries. The blood vessels that only wrap around only the loop of henle are called vasa recta.

Provide an overview of the differences in nutrient reabsorption (i.e. which nutrients—glucose, amino acids, water, sodium, etc.) among the various sections of the renal tubule. Explain why these processes are limited based on transporter saturation.

After your blood enters through the afferent arteriole filtration is taking place, whatever filtrate you are collecting is using hydrostatic pressure and pushing it down into the proximal convoluted tubule, then you have a lot of reabsorption, your body realizes it loosing a lot of stuff, I need sodium, glucose, and amino acids back your body will rescue and start pulling molecule back. It can be passive diffusion or active transport. If you see active - think ATP. So here you can diffuse different type of transporters. (Sodium/potassium/ATP pumps) Water can also come out of these tubules via osmosis. Whenever salt is getting reabsorbed back naturally water has to follow ... that is the rule of osmosis. So when you have that you have small aquaporins located along these tubules that are going to open to let water out. We are going to look at individual sections of the nephron where different things are going to get reabsorbed into the body. Limited based on transporters saturation because when transporters are saturated with the amount of molecules there will not enough left - whatever is left behind will be excreted in the form of urine.

Explain active tubular reabsorption of sodium.

Basically you have the nephron and its located in the kidney and some of them go all the way to the medulla and some of them stay in the cortex but basically the space around the nephron is going to be interstitial space, interstitial fluid also know as extracellular fluid - ECF for short. PCT reabsorption the first rescue that the body does as soon as the hydrostatic pressure kicks in in the glomerulus and pushes the filtrate over into the PCT. Once it is in the PCT - it is the most active section for reabsorption - because you have the primary and secondary active transport taking place. That's where you have a lot of those transporters coming in. So the majority of the glucose and amino acids are going to be reabsorbed back here as well as sodium and water. To use the sodium, you are going to be using the sodium potassium ATP pump, for every 3 sodium out 2 potassium is coming in, that is the rule for this pump.

Define GFR explaining the driving forces and opposing forces involved.

Net filtration When blood is entering in you are basically squeezing that blood out and getting all those micromolecules out and you are forming a filtrate. But what exactly do you need to do to push that filtrate over to the proximal convoluted tubules.. salts and big things like glucose... you have to apply some type of pressure and that's where you have hydrostatic pressure coming in where its going to push whatever filtrate you have in the bowmans capsule into the proximal convoluted tube. So the glomerulus is very porous and you have a lot of capillaries, it is highly permeable because it is fenestrated. This is what allows all those molecules to seep out and get into the bowmans capsule and then eventual apply a little bit of this pressure to push it through the glomerulus into down into the proximal convoluted tubule. And it also has a huge surface area.

Identify the following internal gross anatomical areas and structures of the kidney: renal capsule, cortex, medulla, pelvis, hilum, papillae, column, pyramid, major and minor calyces, renal artery, and renal vein.

So for the kidney external anatomy You have 2 of them, bean shaped structures- they sit behind the abdominal peritoneal wall. The right kidney is slightly lower than the left kidney, because of the size of the liver. The kidney is covered in fibrous connective tissue called the renal capsule, its there to protect the kidney from infection and damage. So the indentation is the renal hilum or hilus, this is where the blood vessels enter in as well as the wreter attached to the kidney. The renal artery supplies blood to the kidneys and the renal vein drains kidney blood to IVC to return to circulation. So you have oxygen rich blood coming in renal artery - the renal artery then branches into arterioles, eventually entering into the functional unit of the kidney where a lot of filtration takes place. And once the filtration takes place that filtered blood leaves out of the kidneys through the renal vein and enters back into circulation. The internal anatomy of the kidney is very similar to the spleen, lymph node and thymus The renal cortex is the outer most layer, the middle region is the renal medulla, and the pale yellow region is the renal pelvis. The narrow part of this is going to be the minor calyx and the flat wider part is the major calex. The indentation where all the blood vessels are merging is going to be called the renal sinus. The individual pyramids are going to be called the renal pyramids or the medullary pyramids. The pointy ends of the pyramids that are facing inward are called the renal papilla. So if you look here you have the renal artery you have the renal artery that is bringing the O2 rich blood into the kidney branching and eventually turns into afferent artery - afferent artery carries blood into nephron and efferent is going to carry blood out of the nephron. So blood basically enters in afferent , goes through the nephron, it gets filtered and then filtered blood exits through efferent arteriol and merges back into circulation. So we said we have a million nephrons - there are a lot of arteriols and capillaries. The way it is set up is to give a large surface area - that way you are able to do a lot of waste excretion and filter out a lot of stuff coming in.

Draw, label and describe the structural areas of the nephron: glomerulus, Bowman's capsule, proximal convoluted tubule, descending loop of Henle, ascending loop of Henle, distal convoluted tubule, collecting ducts.

So the functional units of the kidneys are the nephrons. Nephrons are really small structures that do a lot of waste excretion and blood filtration and essentially produce your urine. You have about a million nephrons located inside your kidney. The renal arteries eventually one of the branches carries blood into nephron through the afferent arteriole. The first part of the nephron is going to be called the renal corpuscle, that has a lot of capillaries, that is going to be called the glomerulus. So in your glomerulus there is a lot of filtration taking place. They are nothing but capillaries that are very porous in nature. They have a lot of holes. The outer structure that is like a little cup, that is called the bowmans capsule. When blood enters it kind of reaches a dead end (bowmans capsule) , the cup prevents blood from going anywhere. So what happens is when we are saying the blood is getting filtered, we have cells that are lined along the bowmans capsule called "podocytes". The podocytes are very particular about what needs to get filtered vs what doesn't need to get filtered. So your electrolytes may slip out, amino acids, glucose but your big stuff like your big proteins albumin are going to stay in the blood. So the capillaries are very porous that's why things are seeping out but you also have the podocytes located along the bowmans capsule that are very particular on what needs to get filtered out. So whatever needs to get filtered seeps sout and stays there, the rest of the blood that is now filtered leaves through the efferent arteriole. From this point of the stuff that got filtered is referred to as the filtrate. And then the filtrate undergoes different types of pressures where it gets pushed into the tubules next to the bowmans capsule - the key is to look at bowmans capsule to locate the PCT (proximal convoluted tubule) So this is where a lot of reabsorbtion takes place. Then from the PCT the filtrate gets pushed down into this hairlike structure called the loop of henle - it has 2 parts to it the descending loop of henle and then the ascending loop of henle going up. We have different things that are being reabsorbed and secreted at these locations. From the ascending loop of henle as the filtrate moves up the filtrate goes up it then goes to the distal convoluted tubule (far away from bowmans capsule). From there you enter into the long stem like structure called the collecting duct. It basically tranverses all 3 layers of the kidneys, why?, excretion of wastes. Finally reaches renal pelvis it now goes to ureter. Filtrate becomes urine

Describe how GFR is intrinsically auto-regulated via the myogenic mechanism (via arteriole constriction/dilation) and the tubuloglomerular feedback mechanism (via juxtaglomerular complex).

So this push the GFR (the glomerular filtration rate) has been using the hydrostatic pressure to push all the filtrate over to the proximal convoluted tubule can be regulated 2 ways. You can have an intrinsic mechanism or a extrinsic mechanism With your intrinsic mechanism this is going to be an inbuilt mechanism where you can do some kind of dilation or constriction to control the amount of blood that is going in vs going out which directly impacts the amount that is getting filtered in your capsule. So this is going to be called myogenic mechanism. So naturally if you are dealing with arterioles - they are made of smooth muscles, so you can dilate or constrict them... or you can do something called tubuloglomerular feedback mechanism via the macula densa - this is where your chemoreceptors for sodium chloride are located and they are constantly keeping those molecules in check. You can use some extrinsic mechanisms by activating your sympathetic nervous system, so you have your epinephrine and norepinephrine kicking and that's automatically going to cause a lot of vasoconstriction, so you will see how vasoconstriction vs vasodilation affects the GFR.

Provide an overview of the three basic processes in urine formation: glomerular filtration, tubular reabsorption, and tubular secretion. Relate these functions to the nephron structures described in Obj. # 3. Describe original components of filtrate and list which components are reabsorbed and actively secreted. See Table 25.1 and Figure 25.17 for assistance.

So we are talking about stuff coming in from the afferent arteriole, we are talking about how it is getting filtered but what is meant by filtration? We have something called glomerular filtration. Basically in the renal corpescule where you have a lot of those capillaries, since its very porous it is basically filtering out all your blood for any type of glucose, small micromolecules such as sodium, chloride, potassium, all of that is seeping out and its forming a filtrate at the bowmans capsule and then its getting pushed out into the proximal convoluted tubule. When it is doing that once it reaches the proximal convoluted tubule you have a lot of reaborbtion taking place. So this is your body's way of doing a final rescue. It is going to save those micromolecules that your body might need, in this case it could be water, glucose, sodium, amino acids... so whatever is getting pushed to the proximal convoluted tubule is getting reabsorbed by the body. And then you are also going to be secreting stuff directly into the tubules through the peritubular capillaries. There is a reason why they are surrounding these big renal tubules. Your proximal and distal convoluted tubules and your loop of henle. There is a reason why they are there, so they can secrete stuff back in. You will see how in countercurrent exchange and counter current multiplication. So after you rescue and reabsorb the molecules and salts into your body water is left behind is going to be urine and then that urine gets transported through the collecting duct over to the renal pelvis and eventually to the ureter and to the urinary bladder.

Describe the two methods of water reabsorption from the renal tubule: obligatory water reabsorption from the PCT, and facultative water reabsorption from the DCT/collecting duct (via ADH).

So when it gets kicked out (reabsorbed). You have water pores through the aquaporins and then you have major electrolytes, magnesium, chloride, potassium. Urea is going to be passive transport.. when we think urea we automatically think of amino acids.. deamination and transamination. Obligatory water reabsorption because anytime salts are coming out you have to have water coming out to dilute that. You have to maintain the tonicity osmolarity concentration of the space, ECF. Then we have the loop of henle, after you reabsorb in the PCT, then you keep the filtrate down the loop of henle and you do a little more reabsorption there. So in the descending portion **** you have a lot of passive transport, passive there because you are only absorbing water. And then as you move up the ascending loop of henle ***** overall in the ascending loop of henle you are going to be reabsorbing salts but the shape changes, thick and thin, the thin part is passive transport but once you get to the thick part you are doing a lot of active transport, Using the sodium/potassium/chloride pump coming in and constantly pumping salts out. So once you do all that then you push your filtrate over from the loop of henle over to the next part of the nephron which is going to be your distal convoluted tubule. The distal convoluted tubule going all the way to collecting duct is under the control of hormones and hormones only. 2 hormones make a lot of decisions - you have the antidiuretics hormone (vasopressin) and then you have aldosterone. ADH gets released from the posterior pituitary and aldosterone gets released from the adrenal cortex. So with the antidiuretic hormone - just like the name suggests, it doesn't want to release the urine, it wants to hold on to the water, reabsorb water, you have decreases urine output. Now you are doing water reabsorption. Aldosterone increases sodium reabsorption in the collecting duct. Whenever you are doing that, you are automatically putting potassium out so potassium will be secreted with urine if aldosterone is being used. When you are doing a transport, using a sodium proton pump or using sodium potassium ATP pump - when you are pumping things in and out.

Provide an overview of the process of tubular secretion and discuss its importance (i.e. which substances are secreted and why).

We have talked about reabsorbing I have also mentioned you have peritubular capillaries that are tightly bound to your tubules and they are also capable of secreting stuff back in to the tubules. So you have these peritubular capillaries, you are moving filtrate along, your body is reabsorbing a lot of stuff but then those capillaries can put stuff back IN to your tubules. It is primarily going to be doing that in the proximal convoluting tubule as well as the collecting duct. So you have drugs that enable this to happen, penicillin, morphine, some blood pressure medication can really affect tubular secretion. And then you have urea - from deamination mechanism. Excess potassium - With hyperchloremia - if you have excess potassium this can be bad, because now you have a smaller refractory period and you can also have random depolarization which is never good. And then you have acidic vs basic control of blood pH. So things that are acidic are getting put in , things that are basic are being put in, depending on blood pH depending on where the body is at. So things that are getting secreted back in to the system. So primarily secretion happen by the PCT - so you see a lot of urea, protein, drugs, medication. Whatever is getting reabsorbed here - water, glucose, amino acids, electrolytes (magnesium, chloride, potassium, calcium) these are pretty much throughout as you are moving along. A lot of active transport is taking place, water, salt are getting reabsorbed and the PCT and collecting duct are under the control of aldosterone and antidiuretic hormone. You can see that, you can see that your antidiuretic hormone is holding on to your water and your aldosterone holding on to the sodium but you are releasing a lot of potassium and you are putting that into secretion. You are taking stuff out and you are putting stuff in as you are moving a long

Identify and provide an overview of the functions of the four organs of the urinary system—kidneys, ureters, urinary bladder, urethra.

With the kidneys there are 4 main organs Kidneys, Ureters, urinary bladder and urethra So the kidneys serve as the major organ involved in the urinary system. These are the ones responsible for doing a lot of blood filtration, waste secretion, maintaining your blood pH, maintaining electrolyte balance in the body - sodium, chloride and potassium. So essentially what they are doing when they are filtering your blood, they are producing urine in the process. Its not necessarily the kidneys but the functional unit of the kidneys that produce the urine. After urine is produced by the kidneys it is transported over to the bladder via the ureters Ureters - are tubules that transport urine from the kidneys to the bladder. Once it reaches the bladder urine gets stored there and you have internal and external spincters that control the release of the urine through the urethra that is released into the environment. So in males and females the urinary system pretty much remains the same EXCEPT the length of the urethra. all of the organs remain the same and perform the same functions

Describe how GFR is regulated extrinsically via the sympathetic nervous system and the renin-angiotensin-aldosterone mechanism (outline this mechanism and know the functions of all hormones involved, as well as the physiological trigger and the physiological result of the mechanism).

You also have another mechanism called the RAS mechanism where you have a lot of sodium that is getting reabsorbed using renin. So when you secrete renin the end result is going to be immediate reabsorption of sodium but you are also going to be letting out a lot of potassium in the process. So here if we are using different dilation/constriction mechanisms to control the amount of blood we are filtering, if we only focus on the afferent arteriole, if you constrict the afferent arteriole there is resistance, so not a lot of blood is going in, that means there is not a lot to get filtered, therefore you are going to get a decrease in GFR. If you dilate the afferent arteriole, there will be less resistance, allowing more blood flow into the glomerulus, more filtration can take place, more stuff can seep out as you increase the GFR. If we look at the efferent arteriole, if you constrict the efferent arteriole, this is going to increase your GFR because blood is not leaving, it is stuck. So the more its stuck the more it gets filtered. If you dilate the efferent arteriole more blood is leaving, there will be less resistance and the GFR will go down.

Distinguish between the capillary beds in and around the various nephrons: glomerular arterioles (afferent and efferent), peritubular capillaries, and vasa recta. Explain the role of each of these capillary beds.

You have something called the juxtamedullary complex (JTC) it has 2 things that are very important. So you have the affterent arteriole, and the glomerulous and this whole thing is going to be your bowmans capsule, close to that is where you have the JTC, where you have these cells, the macula densa cells are basically chemoreceptors. And then right nest to that you have the granular cells... and those are responsible for releasing renin. Renin is involved in the RAS mechanisim...renin, angiotensis, aldosterone mechanism, when blood volume drops. Be able to lable the macula densa and the granular cells. So these 2 together form your JTC complex. The peritubular capillaries wrap around the nephron. The vasa recta wraps itself around the loop of henle.