03. A&P of GU System

In this class, we're going to discuss anatomy and physiology of the GU system, but from a very restricted focus. We're going to look at implications for management of the patient with a urinary diversion. We'll talk about key structures and functions of the GU system very briefly. We'll talk about the impact of kidney function on fluid and electrolyte balance and imbalance, and we'll discuss normal urine characteristics, but again from the perspective of the patient undergoing urinary diversion. Looking first at the kidneys, as you know, the kidneys are located retroperitoneally. That's very important because it means that they're protected against anything that goes wrong in the abdominal cavity. You look at all the patients we have who come in, they have bowel perforation, they have necrotizing pancreatitis, they have a gunshot wound, the kidneys typically are protected against all of that because they're outside the peritoneal cavity. Now there are major zones and we're going to start on the outside and come in. The cortex is the outer zone, and on this slide is that dark red maroon, outer zone, and that's where urine production is initiated, that's where glomerular filtration takes place. And then you have the medulla, which is the inner zone, and that's the lighter pink on the top slide, and that's where urine production is finalized, that's where urine is concentrated through the tubular system. It's also where urine transport begins, and then you have the renal pelvis, which is the portion of the kidney that is continuous with the proximal uritor, and that's obviously all about urine transport. So the major functional structure, you remember this from nursing school, this probably made most of us crazy in nursing school, is the nephron. And you remember that what you have is the glomerulus, and then the renal tubule. So on the top of the slide you see the glomerulus, which is a collection of capillaries surrounded by Bowman's capsule. And that is where urine production begins, that's where glomerular filtration occurs. We'll come back to that. Then you have the renal tubule and the loop of Henley, which you see on the bottom. I'll know all of these are terms from your past. So the renal tubule is actually continuous with Bowman's capsule. There are multiple components, you have your proximal convoluted tubule, which is right there on the top of the illustration at the bottom. So you go from Bowman's capsule into proximal convoluted tubule. Then you go into the loop of Henley, then the distal convoluted tubule, and then the collecting tubule. And that renal tubule plays a critical role in urine production because that's where urine is concentrated. That's where fluid is pulled out of the urine back into the bloodstream. It's also where you actively eliminate waste products, drug metabolites, and where you pull in electrolytes that are needed back into the bloodstream. So we'll talk about that in a little bit more detail in just a minute. Now the other thing you remember about the kidneys is that they receive 15 to 30% of the cardiac output every minute. So the kidneys are normally extremely well perfused. There are two things to remember in relation to blood flow to the kidneys. First of all, we use urine output as an indicator of hemodynamic status. If cardiac output falls, blood flow to the kidney falls, and urine output falls. So way back we all learned that we should be producing at least 30 milliliters of urine per hour. And if we're not doing that, that that suggests inadequate blood flow to the kidneys. We also know that the renal system is very blood flow dependent. It has very high metabolic rate, so needs perfusion, needs oxygenation. And when we have a patient who is hemodynamically unstable, when we have a patient in shock, they're very high risk for acute tubular necrosis. And we've seen many patients come in critically ill. Maybe they're in septic shock. They end up temporarily on dialysis because of the insult to the kidneys. So big take home messages about blood flow to the kidneys. We use urine output as an indicator of renal perfusion and inadequate renal perfusion is very likely to produce acute kidney injury. So the critical functions of the kidneys. Now every one of these are very important. We could go into a lot of detail, but we're going to talk about these pretty briefly. Obviously the number one function of the kidneys is urine production. And urine production is the mechanism about which we eliminate metabolic waste, protein waste. We eliminate toxins. We eliminate byproducts of some drugs. In the process of urine production, the kidneys also play a major role in fluid and electrolyte balance. And in maintenance of acid-base balance. The kidneys contribute to blood pressure regulation through a couple of different mechanisms. The kidneys are responsible for producing the withdrawal poison and for activating vitamin D. So we'll talk about each of those in a little more detail. But we're going to start with the number one function of the kidneys, which of course is urine production. There are two major steps of urine production. The first takes place at the level of the cortex, and that is glomerular filtration. And again, you see the glomerulus at the top left of your slide. You know, you've got this capillary network surrounded by this collecting capsule, a Bowman's capsule. Blood flows into that capillary network under pressure. So it's pumped from the heart into this capillary network, the glomerulus. And a large amount of plasma-like fluid is forced out of the capillaries and collected by that Bowman's capsule. Just so you get a sense of the volume and the importance of phase two of urine production, you actually typically force about 180 liters of primitive urine out into Bowman's capsule each day. 180 liters. Can you imagine what if you didn't have phase two of urine production? What if you had to void and replace 180 liters of urine a day? Your whole life would be in taken output. So fortunately, you have phase two. Phase two takes place along the tubular system, which we've already said is absolutely critical to health. So phase two involves selective reabsorption and urine concentration. So as urine flows through that tubular system, most of the fluid is pulled out of the tubule back into the bloodstream, which converts primitive urine into urine that's ready to void. Because the tubular system is surrounded by the peritubular capillary, so look at the slide on the right, the illustration on the right. So you see the tubular system and you see a network of capillaries surrounding that tubular system. So urine is flowing through the tubular system, large volumes of fluid are being pulled out of the tubular system back into the bloodstream. At the same time, you're actively secreting waste products and drug metabolites into the urine like, take this, I don't want this, I don't need this, give me that water, you take these waste products, oh, I'll take some more of that sodium back into the bloodstream, you can keep this potassium. So you can see that what's happening is urine flows through the tubular system as that is being refined. And the end product is concentrated and contains excess electrolytes, contains protein waste products, contains drug metabolites. The third thing that happens then is we get urine transport. So at the end of the tubular system, urine dumps into the collecting tubule and then through the uratures to the bladder. Let's talk about normal urine characteristics. So the volume ranges from about 750 to more than two liters a day. Very dependent on fluid intake and hydration level and you know that, you know that on days where you're hanging out studying, you're drinking a lot more because you're bored. So you're drinking, you go get another cup of coffee, another glass of water, another glass of whatever. And as a result, you're avoiding a lot more. Then you know that on days when you're at the hospital and you're running around like crazy and you don't have time to drink anything, your urine output falls dramatically. So your output is dictated by your intake. And it's also impacted by levels of ADHD which we'll discuss in a minute and use of diuretics. What about pH? Well, the normal pH of urine is slightly acidic. Typically, urinary pH is somewhere between 4.5 and 6. And that's actually very important to the patient with a urinary diversion. We want to maintain an acidic urine for our patients with urostomies because acidic urine is hostile to bacterial growth. So they're lower risk for urinary tract infection if we can keep the urine acidic. Acidic urine has much less odor which obviously would be very important. And acidic urine is less irritating to the skin because the pH of the skin is also acidic. So our goal in general is to maintain acid pH for patients with urinary diversions. So if our goal is to keep the pH of the urine in the acidic range, we need to think about factors that would affect the pH and what things we should be telling our patients, encouraging our patients to do. The first thing that affects urinary pH is diet. Meat-based diets, interestingly, are more likely to produce acidic urine. Vegetarian diets are more likely to produce alkaline. Being said that we do not recommend a change from vegetarian to a meat-based diet. I wanted you to know that that's not going to be part of your counseling. I probably should have put bullet point two in bold because this is the most important factor, the volume and type of fluid intake. That volume intake typically results in acidic urine, especially if it's water-based. So what are we constantly telling our patients we're encouraging water-based intake? Low volume intake tends to push the pH toward alkaline. Milk-based fluids push the pH toward alkaline. The beverages tend to cause alkaline urine and, interestingly, citrus-based liquids. So orange juice, grapefruit juice. People think that would make the pH more acidic? No. It makes it more alkaline. It has to do with the crab cycle, that's all I can tell you. So volume and type of fluid intake, your take-home message, you're going to encourage your patient to get at least two liters of intake a day, adolescents and adults, and you're going to encourage them to make sure that at least half of that is water-based. Now the third thing that can affect pH is your near-tracked infections, specifically with selected organisms that split urea, produce ammonia and produce alkaline urine. So proteas and pseudomonas are the two most common pathogens that are urea-splitting and that contribute to your near-tracked infection. E. coli really doesn't do this. So if you have chronic infection with either pseudomonas or with proteas, almost always you're going to get chronically alkaline urine, chronically alkaline urine contributes significantly to struvite stone formation. Now those are not common issues, but just things to be aware of. So the most important take-home message is encourage adequate fluid intake, specifically encourage water-based fluid intake. If you have a patient who has chronically alkaline urine and they're either having issues with skin breakdown, issues with odor, issues with frequent UTIs, then you want to look at strategies to acidify the urine. Vitamin C tablets can help acidify the urine. Increased intake of citrus juices will not acidify the urine. Okay, all of these things you know, you know that urine is normally amber to light yellow. You know that if the urine is dark, that typically means not enough fluid intake. You know that urine odor is usually minimal. But if the urine becomes concentrated, odor increases. If the pH changes to alkaline, odor increases. Also, you get increased odor with some foods and some medications. So the number one food that contributes to increased urine odor is asparagus and some people. So some people can eat asparagus and it has no impact on urine odor. Other people eat asparagus, they forgot they ate it. They go to avoid and they're like, "Oh my God, I ate asparagus." It has to do with an enzyme that some people produce and others don't. Bottom line, you want to let the patient know if they're one of those individuals for whom asparagus causes marked increase in odor. They probably want to limit their intake of asparagus to the day when they're going to change their pouch. Because otherwise, they're going to have problems with odor. Medications, the two medications, most likely to increase odor, antibiotics and vitamins. Again, antibiotics are short term. If vitamins cause increase in odor, then you've got to work with that patient. So that odor is not a day-to-day issue. You might need to encourage them to wear a two-piece system and to wear one pouch during the day and one pouch at night and take their vitamin at night. So that odor is confined to their nighttime pouch and doesn't affect their daytime pouch. Specific gravity is like volume. It's going to be extremely variable. We're really not going to spend time on that. Now, what are the normal constituents? Primarily water? Yes, you'll have urea and creatinine because those are the breakdown products from protein that we're actively excreting. Yes, you will have some electrolytes because excess sodium, excess potassium is eliminated through the urine. Mucous is normal. You'll have a few red blood cells, possibly a few white blood cells. You should have no protein, you should have no glucose. If your renal function is normal and your kidneys are healthy, then neither glucose nor protein will pass into the urine. Now we said another function of the kidney is maintenance of fluid electrolyte balance. There's actually a very complicated mechanism, we're going to just talk about the simple high points. So you need to remember that your kidneys are much smarter than you are. They apparently do have a Ph.D. in chemistry, which most of us do not. But here's the bottom line, standard operating procedure for the kidneys. In adequate fluid intake, the kidneys will produce dilute urine. So you know as long as you're drinking plenty of fluid, plenty of water, you're avoiding dilute urine. that is normal. Standard operating procedure. If you are dehydrated for any reason, your NPO, you've had diarrhea. You've had a crazy day at work and didn't get a chance to drink anything, then you are going to produce ADHD. The pituitary gland has Osmo receptors that recognize, oh my gosh, he or she is dehydrated. Then you produce anti-diuretic hormone. Anti-diuretic hormone is sent to the kidneys where it acts on the distal tubules to pull water back into the bloodstream. When you pull water back into the bloodstream, it reduces your level of dehydration and it increases the concentration of urine. So, ADHD is a protective mechanism that helps to prevent dehydration. Notice that ADHD production is increased during periods of physiologic stress, so post-operatively post-trauma and it's common for us to see very concentrated urine and the first 24 to 70 hours post-operatively and then once the physiologic stress comes down, the patient goes through a diuretic phase. ADHD production is blocked by alcohol. So, some of you may remember episodes where you were out with your friends, you were drinking beer or wine or cocktails, probably eating salty things and voiding frequently. Then you wake up the next morning and your mouth is dry as dust and your head is killing you all signs of dehydration. Why? Because alcohol turned off ADHD production and even though you needed ADHD, you didn't get it. So, even though you're moving into the zone of dehydration, you continued to void large amounts. Was the cure? Fluid intake. Continuing in our discussion about the kidneys roll and maintaining fluid and electrolyte balance, so ADHD is what maintains water balance. Audosterone helps to balance sodium and potassium levels. The kidneys secrete, not the kidneys, the adrenal glands secrete Audosterone anytime your sodium levels drop, anytime you become dehydrated, anytime your potassium levels rise past normal. And what does Audosterone do? It causes you to reabsorbed water and sodium and to eliminate potassium. So, ADHD controls water balance, Audosterone controls sodium and potassium balance. Now, one thing you should be aware of, this is a very rare complication, but it can occur. There's something called reabsorption syndrome that can occur in a patient with an Iliol conduit or any kind of uretero intestinal conduit. As we will discuss later, Iliol conduit is the most common form of urinary diversion. And you look at the bottom illustration. So, when you bypass the bladder, you connect the ureters to a little section of Iliom, a little section of bowel. Then what happens is urine is flowing through a section of bowel lined with mucosa. Mucosa is highly absorptive. So, there is the potential that you can reabsorbed sodium and chloride from the urine. And you can excrete potassium and bicarb into the urine as it flows through this section of Iliom. If you do reabsorbed sodium and chloride, if you eliminate potassium and bicarb, you can get hyperchlorimic metabolic acidosis with hypochlamia. I don't want you to spend a lot of time on that. We don't want you to spend a lot of time on that because it's extremely rare. It's extremely rare because as you see in this illustration, most of the time they construct conduits so that they are short and straight, which limits contact with the mucosa and limits absorption. So, it's very unlikely that you would see that. Another function of the kidneys is maintenance of acid-base balance, which of course is critical to health. Now, you know that acid-base balance can be adversely affected by metabolic conditions like diabetic ketoacidosis, also by pulmonary conditions like chronic obstructive pulmonary disease. And why is that? Well, when you think about acid-base balance, you want to think balance. And on one side, hydrogen represents the acid component and bicarb represents the base component. So, with diabetic ketoacidosis, you're hanging on to hydrogen and eliminating bicarb. If you have acidosis because of chronic obstructive pulmonary disease, again, you're hanging on to hydrogen. Now, where do the kidneys come in? Well, remember the kidneys can eliminate unwanted, unneeded ions and can hang on to things you need. So, under acidotic conditions like diabetic ketoacidosis, where you have too much hydrogen, the kidneys will dump hydrogen and retain bicarb. Under alkalotic conditions, where you have too much bicarb, the kidneys will reverse. They'll retain the bicarb and I mean, they'll dump the bicarb and retain the hydrogen. So, basically, the kidneys remember, they're very smart. They determine where do you stand on acid-base balance? Do you have enough hydrogen? Do you have enough bicarb? Are you in balance? Are you leaning to the hydrogen acidoside? Are you leaning toward the bicarb side? And they'll intervene appropriately. So, they'll hang on to hydrogen. If that's what you need, they'll hang on to bicarb if you need that. The kidneys also contribute to blood pressure regulation partially through their role in fluid balance. Obviously, enough fluid contributes significantly to normal blood pressure. When people are fluid compromised, dehydrated, their blood pressure drops. But also through the renin angiotensin mechanism. So, if your blood pressure is low, the kidneys will produce renin, which is then converted to angiotensin, which is a powerful vasoconstrictor. So, yes, the kidneys play a major role in blood pressure regulation. They also produce erythropoetin, which contributes to red blood self-production. We're very aware that patients and chronic renal failure are chronically endemic. They don't have enough red blood cells. So, probably many of you have given erythropoetin to your patients in renal failure. And finally, the kidneys contribute to activation of vitamin D and to normal calcium deposits into the bony matrix. So, the kidneys do a lot for health. We know this. We have a lot of patients with chronic kidney disease. We see all the ways in which chronic renal failure adversely affects health. The next thing we need to think about is urine transports. We've talked about urine production and the use of urine production to control fluid and electrolyte balance to control acid base balance. Now, we're going to talk about transport of urine and storage and elimination of urine. So, the ureters, of course, drain urine from the kidneys to the bladder. The ureters are about 24 to 30 centimeters long and 0.2 centimeters in diameter. So, not very big at all. Very narrow. They are comprised of smooth muscle lined with transitional cell epithelium. So, it is possible to get a transitional cell carcinoma and the ureters in the collecting system, but it's very rare. Transitional cell carcinoma typically occurs at the level of the bladder because the bladder has the most prolonged exposure to the most concentrated form of urine. So could you get transitional cell carcinoma at the level of the renal pelvis along the uratures, yes, but very rare. Now, the role of the uratures, of course, is to transport urine from the kidneys to the bladder. You do have parasitaltic activity. So even when you're lying supine, urine is actively propelled from the kidneys to the bladder. It's not dependent on gravity. You've got parasitaltic activity. That parasitaltic activity is activated by urine in the urator, urine in the renal pelvis, and also by sympathetic stimulation. Urine transport is a low pressure system. So yes, you have parasitaltic, but the pressure within the uratures is relatively low. That's normally fine because pressure within the bladder is normally extremely low. But if you have chronic retention, if you have a very fibrotic bladder wall, then you can get high pressures within the bladder that interfere with urine delivery. That can in turn adversely affect the kidneys because it causes hydro nephrosis. If I can't propel urine out of the kidneys through the uratures into the bladder, then urine accumulates within the entire collecting system, causes pressure on the nephrons and inhibits urine production. There is a very effective anti-reflex mechanism between the uratures and the bladder at the ureterovasical junction. So I want you to notice on the slide to the left, the illustration to the left on top. So you see that dark pink triangle at the base of the bladder. That is also known as the trigon. That triangle is formed by the two ureteral openings and the one urethral opening. When you think about the ureters connecting to the bladder and you realize that they actually insert low within the bladder. They don't connect at the dome of the bladder. They connect at the base of the bladder. So then you think, "Oh, when the bladder contracts to empty urine, what keeps urine from refluxing up the ureters and causing recurrent kidney infections?" Well, there are several things that work together to prevent reflux between the bladder and the ureters. One is the fact that the ureters enter the bladder at an oblique angle. So when the bladder contracts, it tends to swing the ureters closed. Also, you have extra layers of smooth muscle, that trigonal muscle that surrounds the ureteral orifice. So when the bladder contracts, that trigonal muscle also contracts and seals the ureters. So we know that women are very prone to bladder infections, cystitis. But it very rarely progresses to paloma fritis because of this very effective anti-reflux mechanism. So the normal individual with an intact GU system has very good protection against paloma fritis against kidney infections. But what about patients who have a urinary diversion? Is there anti-reflux protection between that section of bowel that conduit in the ureters and the answer is no? So a high priority in management of patients with a urinary diversion is assuring adequate fluid intake so that there is constant urine production flushing the urinary system and preventing migration of bacteria up to the kidneys. And you'll hear that again. Okay, summarizing the bladder very quickly. The bladder is a smooth muscle. It's known as the detrusor muscle. It's lined with transitional cell epithelium, also known as TCC. Transitional cell carcinoma is a very common reason for removal of the bladder, for cystectomy. The bladder has a fixed base in a very distensible body because it goes from almost zero milliliters to somewhere around 600 milliliters when it's full in the average adult. So normal bladder capacity and an adult somewhere between 300, 350 and 600 milliliters among nurses may be a little higher than that. Now the bladder is lined with ureotherium and normally that ureotherium is impermeable to the contents of the urine. So it's actually lined with something called a gag layer glycosaminoglycans and that gag layer does a great job of separating the cells in the bladder wall from whatever is in the urine. There is a condition known as interstitial cystitis and you have intense urgency and frequency and bladder pain. And one theory is that it's caused by a deficiency in the gag layer that allows irritants in the urine to contact the cells of the bladder wall. But normally there's complete separation between the urine and the cells of the bladder wall. As we said the trigon is that triangular area and triangular muscle at the base of the bladder. It surrounds the two uregral openings and the urethral opening. It is both part of the anti-reflex mechanism and a critical landmark. So sometimes you'll see on a cystoscopy report that there is a tumor located within the trigon and then you know it's right at the base of the bladder and very close to the urethral opening. What does the bladder do? You know this from patient care and from your own life. It stretches to store urine, contracts to empty urine and that is what gets bypassed or eliminated in a patient with a urinary diversion. And then last component the GU system, the urethra which of course is responsible for transporting urine from the bladder out of the body. Normally the urethra is closed to maintain a waterproof seal during filling. That's what we want. We won't know drips, no leaks. But we want it to open to provide effective emptying. Men are higher risk for retention because the male urethra is long and curved. It provides great resistance to leakage and to bacterial migration. You hardly ever hear a man say don't make me laugh I'll wet my pants. They're low risk for incontinence. In contrast look at the female urethra short, straight, a couple of inches long. So women much higher risk for leakage, much higher risk for urinary tract infection but much lower risk for retention. So in summary the urinary tract is composed of both the upper and the lower tracks. The upper tracks are the kidneys. The kidneys are responsible for urine production and in the process of making urine they eliminate metabolic waste, they control fluid, electrolyte and acid base balance. The kidneys also contribute to blood pressure regulation. They produce the erythropoietin which supports red blood cell production and they're responsible for activation of vitamin D which controls calcium metabolism and deposition. The urethra is responsible for transporting urine from the kidneys to the bladder. The bladder is responsible for storing urine at low pressures and then for effectively emptying at regular intervals and the urethra is responsible for maintaining a closed door during filling and then for opening completely to provide for unobstructed voidings. And that's it for the GU system. Thank you.