hello everyone today we are going to study the urinary system and these are our learning objectives our urinary system consists of a pair of kidneys a pair of ureters a bladder and a ureter the urine is produced in our kidneys and then it follows through the urinary tract which consists of the organs that transport or store urine so urine is produced in our kidneys then it drains into the ureters which are muscular tubes that through peristalsis carry urine from the kidneys to the urinary bladder at the urinary bladder urine is stored until it is released to the exterior of our body through the ureter so we know our kidneys produced urine but the question is what does urine production means to our body and the answer is that through the formation of urine our body eliminates ions metabolic wastes in extra water that it doesn't need you need to keep in mind how urine is produced in urine is produced from the filtration of our blood consequently depending on how this filtration process is done it can affect our body in different ways and by filtering our blood our kidneys can regulate the ion concentration in our blood plasma and by doing that our kidneys can stabilize our blood pH to the homeostatic levels which is around 7.4 also when our blood passes through our kidneys metabolic wastes are filtered out of our blood and become part of our urine metabolic wastes are biochemical waste right and this is the waste formed from the biochemical reactions that happen in our body and interestingly most of the biochemical waste products are excreted out in our urine not in our feces our faces are mostly food residues into biochemical waste examples that we have in our urine our urea and uric acid urea is the major organic waste product we produce and it is produced from the breakdown of old proteins in our liver the second major organic waste we produce is uric acid which is formed by the breakdown of old nucleic acids so when filtering our blood our kidneys help us to eliminate this metabolic waste and ions but at the same time it helps us to keep to conserve nutrients that do not need to be removed from our body also by filtering our blood our kidneys can regulate our blood pressure by regulating our blood volume so if we eliminate more water from our blood through more information then we can decrease the blood volume which would decrease blood pressure on the other hand if you produce less urine we retain more water and with that we retain our blood volume which could normalize or increase our blood pressure so all these are functions of our urinary system and they are all related to the blood filtration that happens in our kidneys and just to give you an idea of how quick our kidneys are at their job our kidneys filter and clean our entire blood plasma 60 times a day and to do that a huge amount of energy is spent in this tells you how important our kidneys are to keep our body functioning properly now besides these important functions of filtering out of our blood what we do not need in at the same time keeping preventing loss of valuable nutrients our kidneys synthesize calcitriol which is the active form of vitamin D and our kidneys synthesize erythropoietin which is a hormone involved with erythrocytes red blood cells production so what happens is that when our blood oxygen levels are low some of our kidney cells release a hormone called erythropoietin which stimulates our red bone marrow to make new red blood cells hence we say that our kidneys are involved with where it resides red blood cells production so now that we know how important our kidneys are let's talk about where they are located and as you can see here our kidneys are partially protected by some of the vertebral ribs and we usually do not think that our kidneys are these high up our kidneys are outside of the peritoneal cavity and remember when we cover digestive system I told you about the peritoneal cavity and I mentioned that our kidneys ureters and urinary bladder they are all considered retroperitoneal they were in the back of the peritoneal cavity and when we do an ia dissection of a human body if we open up the abdominal cavity and we remove the intestines we would not be able to see clearly the kidneys there because they would be hidden behind the parietal peritoneum since they are behind the peritoneal cavity right so we would need to peel the parietal peritoneum out and then we would be able to see the kidneys so our kidneys are right up against the posterior abdominal wall and surrounding our kidneys we have layers of connective tissue that help with stabilization and protection directly surrounding our kidneys we have a fibrous capsule then we find fat called perinephric fat and peri means nearby right surrounding in Afric stands for the little filtration unit that we find in our kidneys that are called nephrons so perinephric fat is the fat around the kidney this fat around the kidney helps holding the kidney in position and it helps protecting an insulin eating our kidneys because it serves as a little cushion against injury then after the perinephric fad we have the renal fashion that helps anchoring our kidneys to the surrounding structures such as the abdominal muscles that we have in the posterior body well then you can see here we have some more fat over here and then Debbie domino muscles and skin this arrangement all these layers help protecting our kidneys and when someone loses a lot of weight in the amount of adipose tissue the amount of fat to cushion our kidneys gets reduced our kidneys become more vulnerable to traumatic injuries so now you have an excuse to not lose weight because you want to protect your kidneys now looking here at this diagram on the Left we can notice that our right kidney is a little lower than our left kidney and the reason for that is because we have deliver the right liver lobe right above the right kidney and if you recall the liver is the biggest visceral organ we have and the right lobe is huge and is located on the upper right side of our abdominal cavity so because of our liver our right kidney is pushed down a little bit and then once again we can look symmetric another thing we can observe in this diagram is the inferior vena cava and aorta specifically the abdominal aorta in branching of the abdominal aorta we have the renal arteries and each window artery goes into each kidney and then they branch up several times until capillaries are formed and at the capillary level excess water excess ions and metabolic wastes are filtered out of our blood in this filtrate after some other modifications it turns into urine and then the urine into this muscular tube called ureter and urine goes down the ureter and it's collected in this muscular sac called urinary bladder when the urinary bladder is full and it is appropriate to urinate urine leaves the urinary bladder and travels through the urethra and gets out of our body in this diagram we have the anterior view of the abdominal pelvic cavity and we can see once again that our right kidney is a little lower than our left kidney and located right above our kidneys we find the adrenal glands and these glands are also known as suprarenal glands because they are located right above our kidneys in this glands the suprarenal glands or adrenal glands they are endocrine glands that produce several hormones including adrenaline and cortisol also in this diagram we can see the hilum of our kidneys and helium is a word I mentioned before right we talked about the hilum of our lungs which was the point the area of entrance and exit of blood vessels nerves and also the entrance of the main bronchus now here in the kidneys the hilum is the place where blood vessels and the renal pelvis will pass through and when we look at this frontal section through the left kidney we can have a better view of the renal pelvis passing through the hilum now let's analyze this diagram that we have here we see that our kidney has an outer layer which is called cortex and we heard the word cortex before right for example our cerebral cortex which is the most outside part of our cerebrum so the cortex here is the outer layer of our kidney then we have the inner layer which is called medulla and the medulla has these triangular structures which are called we no pyramids the tip of each renal pyramid is what we call renal papilla in popular means nipple so apparently these little structures that we see here they look like nipples at the very tip of the renal popula we find the place where urine drips out and then urine goes into a space called minor calyx and the minor calyx urine cannot be modified any further once urine gets into the minor calyx that's it all substances found in the urine present at the minor calyx will be eliminated from our body when we urinate when minor calyx come together they form what we call major calyx and the major calyx drains into the renal pelvis and that leads to the ureter that takes during vera parish houses so muscular waves of contractions for steering to go into the urinary bladder here we have the same fromto section of the left kidney that we saw before but in this one we have a better view of the blood vessels and I mentioned before that the renal artery branches off the abdominal aorta and when the renal artery enters our kidney it starts to branch out into different vessels until it branches so much that it turns into the capillaries that filter our blood and this chart flow tells us the name of the vessels every time we have a new branch now lookie here at the kidney we can observe that after the renal artery enters the kidney it branches into the segmental artery then the segmental arteries branch into the interloper arteries which then makes this little torn that looks like an arch and then they're called arcuate arteries and then branching off the arcuate artery we see these little branches that are like radiating into the cortex region of the kidney and these vessels are called cortical radiate arteries now from the cortical radiate artery we have the efferent arterioles branching off and the afferent arteriole branches into capillaries which are the filtration system of our blood these capillaries are called glomerular capillaries in the group of capillaries is referred to as glomerulus after the glomerulus the group of glomerular capillaries the efferent arteriole is what takes the filtered blood out and then the efferent arteriole becomes capillaries again which are named peritubular capillaries but also if variant arterioles can give rise to what we call Vasa recta and we'll talk about peritubular capillaries and Vasa recta soon afterwards dispirit tubular capillaries and the resurrector will drain into venules and then after the venues will find the cortical radiate things then the arcuate veins then the interloper veins and finally the renal vein that you drain into the inferior vena cava now what I really want you to know is that we know arteries arrive at the kidney in the branch off several times and then we have the eighth variant arteriole and that's where we start this a fair inter Theriault is what brings and becomes the goal malar capillaries which collectively are called glomerulus leaving the glomerulus we have the efferent arteriole and the efferent arterial branches forming another capillary called peritubular capillary and also they can form the Vasa acta after the peritubular capillaries and the Vasa recta blood drains into venules and then blood eventually reaches the renal vein that drains into the inferior vena cava and here we have magnified what happens when the afferent arteriole branches up and gives rise to the glomerular capillaries which are collectively called glomerulus and then after the glomerulus the blood follows through the efferent arteriole and looking here at the bottom diagram you see that the efferent arteriole branches up again giving rise to the peritubular capillaries but also it can give rise to the Vasa recta and after blood passes through this peritubular capillaries and the Vasa recta blood to eventually drain into venules that will drain eventually into the renal vein that drains into the inferior vena cava and this is what you need to know so look here they go maro our capillaries we have this very funny-looking cells surrounding it because we can just see the capillaries in these little red sections that we see there in surrounding the capillaries then surrounding the Patino cells that make up the capillary walls we have these cells called podocytes and podo means feet right in these cells they look like they have little feet in between the feet between those projections we see the endothelial cells that form the capillary they go marival capillaries and through these little spaces which are named filtration islets is where blood plasma with substances in it will leak and then whatever was filtered out of our blood ends up in this space called capsular space and then it will follow through a system of tubules that we are seeing here all these purple tubules now look at this surrounding the glomerular capillaries we have this capsule that's called glomerular capsule or Bowman's capsule and between the glomerular capsule in the glomerular capillaries we have a space and in this space we will find whatever leaked out from the capillaries so all that was filtered out of our blood will end up going into this capsular space and then this filtrate will have no other option than to follow through the system of tubules that we see here and that's why whatever that was leaked out of the glomerular capillaries is referred to filtrate or tubular fluid so after the capsular space this filtrate or tubular fluid will go into the proximal convoluted tubules and the proximal convoluted tubule is called proximal because it's the one that's proximal to where the blood was filtered and it's convoluted because it's all coiled up so we have the filtrate going from the capsular space into the proximal convoluted tubule and then it goes into what we call nephron loop also known as loop of Henle and the nephron loop has the descending limb in the a sending lamp and then after day sending lamp we have the distal convoluted tubule which is the coiled up to be oh that's distant from where the blood plasma was first filtered then after the distal convoluted tubule the tubular fluid goes into the connecting tube U and then into the collecting duct and as you can see here the collecting duct collects tubular fluid from several connecting tubules and then eventually these tubular fluid turns into urine and that will be released into the minor calyx now when we talk about the glomerulus together with the glomerular capsule we say we know corpuscle and when we are talking about the proximal convoluted tubule plus the nephron loop plus the distal convoluted tubule we say we know to beYOU and together the renal corpuscle plus the renal tobio forms one nephron and the nephron is the filtration unit of our kidneys so here we have again the frontal section of our left kidney and we can see the cortex and the medulla of our kidney and we can see that we have two main types of nephrons we have nephrons that are mostly located in the cortex of our kidneys and we have nephrons that are mostly located in the medulla of our kidneys and the nephron that's located mostly in the cortex is called cortical Ephraim in the nephron that's mostly located in the medulla of our kidney is called juxta medullary nephron now let's look at these into more detail we have the renal corpuscle of the cortical and the juxta medullary nephrons and both renal corpuscles are present in the cortical region right in the cortex of the kidney and the same happens for the proximal convoluted tubule then we have the nephron loop and the nephron loop is divided into descending limb and ascending limb and that's where we see the biggest difference between the cortical and the juxta medullary nephron is the length of the nephron loop that dives into the medulla so the juxta medullary nephron goes deep into the medulla and the court cone Ephraim doesn't go as deep then after the nephron loop we have the distal convoluted tubules that connects with the collecting duct now all that's filtered out of our blood goes into the capsular space right and then this fluid is this filtrate is transported along the nephron tubules and when it is transported along the nephron tubules it gets modified because reabsorption or secretion happens along these tubules all the way until the collecting duct and then some final modifications are done at the collecting duct level and urine is finally formed so the tubular fluid goes through this system of ducts and gets modified in the main modification that happens at the level of the nephron loop is related to concentrating the urine and now since we know that the nephron loops are related to concentrate in the urine it becomes significant to differentiate the cortical nephrons from the juxta medullary nephrons because the juxta medullary nephron since they have a very huge nephron loop they will be related to concentrating the urine on the other hand the court Corps nephrons will not have that ability as much as the juxta medullary does so in our body we have most of our nephrons our cortical nephrons because our urine is not that concentrated we have a lot of water in our urine right so 85% of our Nationals are cortical nephrons and just 15% of our nephrons are juxta medullary nephrons because our urine is not that concentrated our urine is watery which means that our urine has lots of water in it and if we compare our urine to the urine of some mammals that live in the desert you'd see that memo's that urine is very viscous it's very like a paste and that's because the amount of juxta medullary nephrons they have is very high and the juxta medullary nephrons concentrate their urine so much that it turns into a paste okay let's keep dissecting our nephron so the natural hands forming parts right it starts with the renal corpuscle and that leads into the proximal convoluted tubule which is this coiled up to build its proximal to the renal corpuscle then the proximal convoluted tubule leads into the nephron loop and there we have the descending limb and the ascending limb and that leads into the distal convoluted tubule that leads to the connecting tube you that connects with the collecting duct now the nephron goes from the vinegar Paso to the end of the distal convoluted tubule and we will go over every single part of the nephron and figure out what they do there are three key mechanisms that nephrons use for urine formation and the first one is filtration which is the process of filtering or forcing fluid across the semipermeable membrane and filtration happens at the glomerular capillaries right in these capillaries are fenestrated capillaries they have little pores remember when we talked about capillaries I mentioned that we had three different types of capillaries we had the continuous capillaries the fenestrated capillaries in the stillness oído capillaries the fenestrated is the one that had little pores and this is the one that we find here in the glomerular capillaries so we have these little pores allowing filtration to happen surrounding the glomerular capillaries we find cells called podocytes that I showed you in the previous slide in this photo sites they have little faith little extensions in between these faith we see the glomerular capillaries this endothelial cells shining through and those are the places where blood plasma will be filtered so it will be able to leak out from the inside of the capillary so filtration only happens at the glomerulus at the glomerular capillaries and what gets filtered out in the glomerular capillaries cannot be the big right because the pores are very small they are fenestrated capillaries so we have a small molecule such as water ions metabolic wastes amino acids in certain gases being able to cross to pass through these little gaps but cells are too big to cross these little gaps so red blood cells white blood cells large proteins they can't cross the filtration membrane so they stay in the blood stream if red blood cells could pass through this filtration system it would be normal to find blood in our urine and that's not the case right we know something is wrong when we see blood in the urine and that's because we know that red blood cells should not be filtered out of our blood when passing through these glomerular capillaries so under normal circumstances just a small substance are capable of crossing the glomerular capillaries now after the filtration mechanism we have the tubular reabsorption and then the tubular secretion happening tubular reabsorption means that we actually move substances from the tubular fluid back into our tissue fluid which can then get reabsorbed back into our bloodstream so reabsorption is the process of reabsorbing moving fluid that is inside of the tube you back into the interstitial fluid and and it goes into our bloodstream so what would you expect to get reabsorbed what would you not want to lose in the urine and we do not want to lose in our urine any nutrients that were small enough to lick out of our blue Mara capillaries but we do not want metabolic wastes being reabsorbed right so we can conclude that reabsorption is a selective process and we select what will be reabsorbed and that involves transport proteins that use ATP to move molecules across the tubular membrane and that's where we have lots and lots and lots of energy being spent to form a urine the way it should be formed because we need to reabsorbed all that was leaked out but should not leave our body so we spend energy doing that we use ATP to do that now secretion is the opposite of reabsorption so tubular secretion takes substance from our bloodstream and interstitial fluid and then put them into the nephron and what do you think our body would want to secrete into the nephron and the answer is toxins toxins that or not is more enough to leak out of the glomerular capillaries then our body spends energy to pump them into the nephron and then that way it leaves our body as fast as it can because our body treats them as toxin so filtration happens at the glomerular capillaries and then whatever was filtered out of our blood goes into the proximal convoluted tubules and at the proximal convoluted tubule is where most reabsorption happens we have the reabsorption of 60% of the sodium and chloride ions that were leaked out and we have reabsorption of some water as well we have organic nutrients and plasma proteins being reabsorbed and what allows the proximal convoluted tubule to reabsorb things very well is the fact that the cells that blind the inside of the proximal convoluted tubule are simple cuboidal cells like all other cells that make up the tubules but these cells in the proximal convoluted tubule have lots and lots and lots of micro villi in these micro villi increase the surface area for reabsorption so lots of reabsorption happens here at the proximal convoluted tubule so if any nutrients are leaked out by the filtration system these nutrients are reabsorbed right away at the proximal convoluted tubule now in the nephron loop we get both reabsorption and secretion and interestingly in the descending limb of the nephron loop we get reabsorption of water and then in the ascending limb we have the reabsorption of sodium and chloride ions so the descending limb is named descending because as the filtrate flows through it the filtrate goes from the cortex down it descends into the medulla and then we have the filtrate being forced back up so a sending from the medulla back into the cortex and that is the a sending them what's important to know about the descending limb is that the cells in the descending limb are only poor mobile to water not to ions so as fluid is being forced down the descending limb only water is being reabsorbed at this point so if only water is being reabsorbed as the tubular fluid is going down the descending limb that means that we are creating a smaller volume that's highly concentrated in ions because if you're removing water from the filtrate what's left behind is a smaller volume with lots of solutes in it and that's one week all concentrated now when we get to the a standing limb the cells that line the standing limp are not permeable to water they are only permeable to sodium and chloride ions and then what happens is that in the cell membrane of these cells of the a standing limp we find lots of sodium and chloride active pumps so pumped that use ATP to actually pump sodium and chloride from the tubular fluid into the interstitial fluid and that's called reabsorption so when these ions are removed we are actually d concentrating the tubular fluid so what that means is that the nephron loop concentrates and then D concentrates the tubular fluid and in reality what happens is that water is pumped out of the descending limb because of the osmotic gradient created by the ions that are pumped out in the a sending limb so by the end of the nephron loop we have a smaller volume of diluted tubular fluid then in the distal convoluted tubule what's interesting is that it is sensitive to lots of hormones in hormones that influence the kidney they would typically act at the level of the distal convoluted tubule or collecting duct so for example if we talk about antidiuretic hormone ADH this hormone it acts by increasing the amount of water channels in the distal convoluted tubule and collecting duct cells in these water channels are called aquaporins and by putting more water channels in the distal convoluted tubule and collecting duct cells ADH antidiuretic hormone facilitates water movements through osmosis so in the absence of ADH water is not be absorbed at the collecting duct and when our blood osmolality is too high so the amount of solute in our blood is too high our pituitary gland senses it in then it releases ADH and then ADH stimulates the reabsorption of water in the cells that make up the distal convoluted tubules and collecting duct so more water is retained in our body less water is released in our urine so what ends up happening is that we produce a small volume orphan urine that's highly concentrated another hormone that affects the distal convoluted tubule is aldosterone and the way our daughter on works is that it aids in potassium secretion and then what aldosterone does is to actually help remove potassium from our body and then secrete that potassium into our distal convoluted tubules and at the same time aldosterone aiding sodium reabsorption so the point I'm trying to make is that the distal convoluted tubule can be affected by hormones on the other hand nephron loops are not really sensitive to hormones a nephron loop to always do the same thing under normal circumstances now the collecting duct as I mentioned before they are sensitive to antidiuretic hormone and then they prevent Diras so it prevents water loss right so when the collecting duct is under the influence of antidiuretic hormone it will help to produce a highly concentrated urine because it stimulates the absorption of water from the collecting duct now my question is can we call the fluid that we have inside the nephron urine and the answer is no we cannot call it urine because what we have inside an alum is the tubular fluid or filtrate that gets modified all the way until it gets into the collecting duct and if there is presence of ADH antidiuretic hormone that hormone will act in the collecting duct and will keep modifying the tubular flow we can just call urine when it's out of the collecting duct and that's when it reaches the minor calyx so the first part where we can call urine urine is the minor calyx now I mentioned previously that the efferent arteriole branches up and gives rise to the peritubular capillaries and Vasa recta and here you can see that these capillaries they are in strategically located surrounding the renal tubule and there is a reason for them to be there that's why call is strategically located these capillaries are there to pick up to put back into the bloodstream all substances that were reabsorbed from the tubular fluid as well as to secrete into the tubular fluid toxins and ions that our body wants to excrete so for example all water that was reabsorbed from the descending limb and went into the interstitial fluid now goes into these capillaries and then is added to our blood volume but now there is a difference between the cortical and the jaxa medullary nephrons remember the juxta medullary nephrons or the one that went deep into the medulla and they have very deep long nephron loops and when we have this deep long straight nephron loops we have the Vasa recta so we just find Vasa recta in the juxta medullary nephrons and we do not find Vasa recta in the cortical nephrons in the court cone ephram's we find the peritubular capillaries so we find the peritubular capillaries surrounding the window tube you off the cortical nephrons and we find peritubular capillaries surrounding the distal convoluted tubule in the proximal convoluted tubule off the juxta medullary nephrons but surrounding the nephron loop of the jokester meddler nephrons we have Vasa recta now that we have a better understanding of what the from thus we can look at how it is organized in real life in in real life what happens is that they end the very end of the nephron so the distal convoluted tubule associate with the beginning of the nephron which is the window kirpa so in this association forms a complex called juxtaglomerular complex in the cells present in these juxtaglomerular complex they are very important in the aid in the process of measuring substances and blood pressure so making this juxtaglomerular complex we have the macula densa cells the juxtaglomerular cells and the extra glomerular messenger cells the American audience of cells are found in the distal convoluted tubule right next to the efferent arteriole in these macula densa cells have chemo receptors that sense the fluid inside of the distal convoluted tubule and they measure the concentration of sodium chloride present in the tubular fluid and that's very important because by measuring sodium and chloride present in our tubular fluid these cells can understand what our nephron did since we are looking at the end of the nephron so if the sodium chloride content is high by the time the fluid gets to the end of the nephron that suggests that the fluid moved too quickly through the nephron and there was not enough time to reabsorb substances now if the concentration of sodium chloride in the filtrate sensed by the macula densa cells is too low that suggests that our tubular fluid moved through the nephron to it slowly which means we have too much time to reabsorb sodium and chloride so the purpose of the macula densa cells is to measure sodium and chloride in the filtrate at the level of the distal convoluted tubule you know if that indirectly understand how fast the tubular fluid is flowing is moving through the natural another type of cells that we find the just a glomerular complex are named juxtaglomerular cells and these cells are basically smooth muscle cells and they all of the afferent arteriole and their function is to effectively measure the pressure of the blood that's gaining into the glomerular capillaries these cells have Makino receptors in the measured a stretch on the efferent arteriole so if our a fermenter tell you is really stretched that suggests our blood pressure is high and then this just a ghulam error cells can actually contract to prevent damage to our glomerular capillaries because if our blood pressure is too high that could potentially pop the glomerular capillaries so the just a common learn sound since if there is too much stretch and they can contract and with that the veins o constrict the afferent arteriole and that reduced blood flow into the glomerular capillaries which protects the glomerulus on the other hand if blood pressure is too low they just a chimera cells don't stretch enough and then this cells release a hormone called raining and raining is a hormone but it is also an enzyme and when raining gets released in the bloodstream it converts angiotensinogen to angiotensin one and under tension one is converted into under tensing 2x8 enzyme which is in the capillaries of our lungs then endo tensing chu has four main effect in our body which are all related to increase blood pressure angiotensin 2 makes us thirsty it causes the release of our Doster it causes the release of antidiuretic hormone and it is a vasoconstrictor so the overall function of raining is to increase our blood pressure and that's all I need you to know that when the justa glomerular cells do not stretch enough they release raining and raining leads to the increase of our blood pressure now the last cells we have in the juxtaglomerular complex are called extra glomerular messenger cells in these cells are messengers they facilitate the communication between the macula densa cells and the juxtaglomerular cells now we know how you rings formed and after it's formed it goes into the minor calyx then after the minor calyx it goes into the major calyx then we know pelvis and then it goes into the ureter we have a pair of ureters which are muscular tubes that originated at the renal pelvis and extend down and connect to the posterior wall of the urinary bladder where they drain urine into the bladder when we look at a transverse section of a ureter we see that lining the lumen of the ureter we have transitional epithelium and if you recall transitional epithelium is a type of stratified epithelium we have several layers of cells but these cells can stretch and recoil back to the original shape in order to adapt to the degree of this tension needed so we find transitional epithelium lining the lumen of the ureter and and also lining the lumen of the urinary bladder that I will be talking soon then we have here is mouth muscle layer and this is move muscle fibers will move urine through peristaltic waves of contractions into the urinary bladder so if you are lying down or if you are upside down urine will go from the kidneys into the urinary bladder because urine is moved through peristaltic waves and then after the smooth muscle layer we have the advantage layer which is the outermost layer that basically anchors the ureter to the surrounding tissue now the ureters attached to the urinary bladder posteriorly right in that area is called Trigon and here we can see the Trigon in the two orifices through which ureters deliver urine into the urinary bladder in this Trigon is like a funnel that funnels urine into the urethra and it is clinically relevant because since it is at the base of the urinary bladder very close to the urethra it's a common place for infection to happen now lining the lumen of our Union airy bladder we have transitional epithelium just like the epithelium we had inside of the ureters and there is also roogie which are folds that allow for expansion so our urinary bladder can stretch now we see here the detrusor muscle and this muscle forms the wall of our urinary bladder and that's when I will refer to our urinary bladder as a muscular sac that stores during when the detrusor muscle contracts it squeezes the urinary bladder and forces urine into the urethra the in urine is eliminated from our body and we see here that continues with the the truther muscle at the junction between the urinary bladder and the urethra we have the internal urethral sphincter and when this finger relaxes urine can go from the urinary bladder into the urethra now since we see here the urethra passing through the prostate we can conclude that this diagram is showing us the urethra of a male and here we have a lateral view of the male urethra and sensory is very long depending on where its passing through it receives a different name so the segment of the urethra that's passing through the prostate gland receives the name of prostatic urethra after that right under the prostate gland we have the external urethral sphincter that little piece of urethra that's passing through the external urethral sphincter is called membranous urethra now after the membranous urethra we have the spongy urethra and this is the longest section of the male urethra and it goes through the corpus spongiosum which is one of the two erectile tissues I will talk about when I cover the male reproductive system so this point Jewry truck goes all the way down and it ends at the external literal orifice now when we compare the menu in the female urethra we can easily notice that the male urethra is much longer than the female urethra and that's one of the reasons why males have much lower incidence of urinary tract infections than women and another very important fact is the one that I mentioned when we covered the digestive system and that's related to the wiping issue that some women have some women they wipe in the wrong direction they wipe from back to front and that can bring bacteria from the digestive system into the urinary system because the female Reacher is very short women become more susceptible to urinary tract infections because bacteria do not need to go too far to be able to get into the urinary bladder and cause problems in men because the urethra is very long bacteria needs much more time and this time that the bacteria needs to travel through the urethra it gives enough time for the white blood cells to take care of them and prevent the infection and besides that it is believed that the prostate gland produces it's equation that actually prevents me from getting urinary tract infections another difference that we see between males and females urethra is that in men the urethra is shared between the urinary and the reproductive system on the other hand in females the urethra is not shared with the reproductive system so to break any kind of misunderstanding women do not urinate from their vagina even though a lot of people think that so here we see the uterus the place where the fetus grow and then we can see that the vaginal canal is a different tube than the urethra now in both males and females the urethra extends from the bladder and right at the junction of the bladder with the urethra and continues with the detrusor muscle that makes the wall of our urinary bladder we find the internal urethral sphincter both the detrusor muscle and the internal urethral sphincter are made of his muth muscle fibers we do not have control over them and then a little further down the yudhishtira passes through the external urethral sphincter and then it keeps traveling until it reaches the external urethral orifice which leads to the exterior of the body the external urethral sphincter is made of skeletal muscle fibers so we do have control over it the detrusor muscle is a smooth muscle fibers we do not consciously control the contraction of our urinary bladder and also made from a smooth muscle fibers is the internal urethral sphincter now urination is coordinated by a reflex that's called micturition reflex in micturition is the clinical world for urination so what happens is that when our bladder is full the stretching of the bladder is stretched baroreceptors that then send information to the spinal cord in the end to our brain and then we become aware that we need to urinate these leads to the contraction of the detrusor muscle and relaxation of the internal urethral sphincter when they smooth muscle fibers that make the detrusor muscle contract they squeeze our urinary bladder and then it forces urine out in at the same time the relaxation of the smooth muscle fibers that make the internal urethral sphincter leads to the opening of the internal retrace filter and then urine from the urinary bladder can pass into the urethra now the only reason we do not urinate when it's not appropriate is because we contract the skeletal muscle fibers that make up our external urethral sphincter because we do have conscience control over skeletal muscle fibers right so we keep squeezing the external urethral sphincter until it is appropriate to urinate and that's more or less the same situation we have with the internal and external anal sphincters so we have the internal urethral sphincter which is made up offa smooth muscle fibers relaxing but we can squeeze the external urethral sphincter that's made of skeletal muscle fibers and then we do not urinate when is not appropriate and with this we finish the urinary system please let me know if you have any questions bye