Hi, let's talk about the functions of the urinary system. Now, the urinary or the renal system has three major categories of what it does for the body. The first is the maintenance of extracellular volume and osmolarity. If you think about all of the fluid in your body, you have blood plasma, you have interstitial fluid, you have cerebrospinal fluid, you have lymph and so on and so forth. It's important to be able to regulate the volume of all of the body's fluids and also the various concentrations of the solutes dissolved in the water. So we might presume that the renal or the urinary system is important for regulating the concentration of ions for the body. So that's going to be important. And on a related note to that, there are certain ions that are going to be of supreme importance in helping to regulate the pH of body fluids, namely protons and bicarbonate ion. By being able to selectively either keep or excrete things such as protons and bicarbonate, the urinary system is able to help maintain the body's pH homeostasis. So normally or typically these tissues are maintained between 7.35 to 7.45 on the pH scale. That's considered physiologically neutral. Going hand-in-hand with this, the urinary system also is able to regulate water volume for the body by choosing to either keep the water within the body or excrete it in the urine. And then finally, the urinary system is very good at being able to maintain the concentration of glucose in the blood and other tissues. So for instance, the typical renal clearance of glucose is 0, meaning that the kidneys selectively keep all of the glucose that makes it into the filtrate. So that is reabsorbed back into the blood. Now, rounding about the threshold of about 160 to 180mg per deciliter, that's 100mL, glucose begin to be excreted into the filtrate. The kidneys are also good helping to regulate glucose in terms of going through a process called gluconeogenesis, or the creation of glucose from other materials. And so as we can see here, this isn't an exhaustive list, but these are some of the highlights of the substances that the kidneys are helping to maintain in concentration within the bodily fluids. Next, the kidneys are actually very adept at performing endocrine functions. So there are three major hormones that we want to look at here. There's calcitriol, erythropoietin, and renin. Calcitriol is an important part of calcium homeostasis, and in fact, it's an activated form of vitamin D, which is an important diet co-factor for the absorption of calcium across the gut walls. So without calcitriol or activated vitamin D, the body really isn't able to capitalized on the calcium that's lying in the lumen of the gastrointestinal tract. Also important is erythropoietin. So EPO is secreted by some of the cells within the kidneys in response to being in a hypoxic environment. And as we've talked about in the cardiovascular system, whenever the body's level of oxygen has been below threshold for an extended period of time, the kidneys are going to release EPO. And that's going to cause the red bone marrow, the hematopoietic connective tissues within the bone, to begin to produce more erithrocytes. And this is a process that can take about ten days. And then finally, your kidneys also secrete renin in response to a decrease in blood pressure. And what happens here is that renin actually is the first part of the RAA pathway. RAA stands for renin-angiotension-aldosterone, and it's actually a rather complex pathway by which various substances are secreted and then catalyzed into other substances. Such that your body is able to increase blood pressure, or at least resist a decrease in blood pressure. So anytime that a person is in danger of experiencing hypovolemic shock, or having too little blood in the cardiovascular system to function, the kidneys are actually one of the first things that step up to help save the body hormonally with their secretion of renin. The final category would be excretion as a function of the urinary system. This is probably one of the more obvious functions of the system. So any of the catabolic wastes, so as the body is going through the processes of metabolism, any waste products that are dissolved within the blood, the kidneys are very adept at secreting. Sometimes these waste products aren't secreted to their fullest capacity to support other processes, but the one of the main pathways of having materials leave the blood would be through the kidneys in the production of urine. And finally, bioactive substances are able to be filtered by the kidneys. And so by bioactive substances, we are talking about things like pharmaceuticals and other substances that may have an impact on physiology. Your kidneys are one of several locations where such substances may be filtered and excreted. So we've talked a little bit about how your urinary system is able to maintain extracellular volume and osmolarity and function and the capacity of an endocrine organ, and how they work in terms of the body's pathway of excretion. Thank you.
