Urinary System Module 10 PDF

Module 10: Urinary Physiology The Urinary System Consists of - Kidneys (2) - Ureters (2) - Urinary Bladder (1) - Urethra (1) Functions - the urinary system is the principal means of waste removal - the ureter is what brings the urine that was formed out from the ki...

Module 10: Urinary Physiology The Urinary System Consists of - Kidneys (2) - Ureters (2) - Urinary Bladder (1) - Urethra (1) Functions - the urinary system is the principal means of waste removal - the ureter is what brings the urine that was formed out from the kidney, and follows down to the urinary bladder The Kidneys - The major organ responsible for forming urine - The role of the kidney is to go through our entire blood supply and pick out the waste, and return the stuff we want to keep, back to our general circulation - The renal artery welcomes blood into the kidney - The renal artery once it has entered the kidney, will split off and branch out into smaller arterioles that follow through the renal cortex - The functional unit of the kidney is the nephron, which is in charge of the actual sorting of blood. - After the blood has been filtered, it will leave through veins in the renal cortex eventually following out through the renal vein - The urine that we do form is then captured in the minor calyx, and then it will collect and congregate in the renal pelvis, then out the ureter and stored in the bladder until the body urinates Functions of the Kidney 1. Filters the blood plasma, filters out the waste from the plasma 2. Regulate your blood volume and pressure, by regulating how much water we retain and how much water we urinate. The more water that there is in your blood the higher the blood pressure 3. Regulate the osmolarity of the body fluids: by controlling the relative amounts of solutes eliminated in urine 4. Secretes the enzyme renin, which activates whole hormonal systems that maintain blood pressure  5. Secretes the hormone erythropoietin, which stimulates the production of red blood cells The Nephron - has two components to it, the blood component where all of our blood vessels are, and the second component, is a series of tubes that will contain urine. - These components are also known as a vascular component and a tubular component - All nephrons start in the renal cortex and and follow inferiorly into the renal medulla The Fluid in the Vascular Component of the Nephron - is whole blood - is continuous with your general circulation - if fluid is in the vascular component, its being kept by the body Tubular Component of the Nephron - Contain the filtered blood plasma! - Contains the filtered out waste products aka filtrate - The filtrate will eventually be excreted out as urine The Nephron - Vascular Component - The Renal Artery brings in blood that has not been filtered out by the kidney yet - After the renal artery, the afferent arteriole brings the blood supply into the glomerulus. - It’s the blood in the glomerulus that is being filtered out - The blood leaving the glomerulus via the efferent arteriole - Following the efferent arteriole, the capillary network that surrounds the convoluted tubules is known as the peritubular capillaries. They surround the majority of the nephron and mainly communicate and exchange with the tubular component of the nephron. - The peritubular capillaries come together at the end to eventually form the exit out of the nephron, the renal vein. The Nephron - Tubular Component  - The tubular component of the nephron is made out of single epithelial cells making it ideal for diffusion and also making it possible for some of the filtrate to return to the peritubular capillaries 1. Bowman’s Capsule - A doubled walled cup that houses the glomerulus catches things that are being filtered out of the glomerulus, such as fluid and waste products 2. Proximal Convoluted Tubule - Shortly following Bowman’s Capsule, the PCT help us retain salt and water 3. Loop of Henle - a dip into the renal medulla, that has a thinner tube when dipping into the medulla versus a thicker tube when leaving the medulla 4. Distal Convoluted Tubule + Collecting Duct - DCT is the final zone of the tubular component that joins with the collecting duct where other nephrons will form as well. The collecting duct will eventually lead you to the renal pelvis and the ureter Flow of Filtrate in the Kidney STARTS in Bowman’s Capsule -> PCT -> Loop of Henle -> DCT -> Collecting Duct -> Renal Papilla -> Minor Calyx -> Major Calyx -> Renal Pelvis -> Ureter -> Urinary bladder -> ENDS in the Urethra - Filtrate: the filtered blood plasma that contains waste products Types of Nephrons - the main distinguishing factor between the types of nephrons is their length according to their loop of henle Cortical Nephrons - 85% of all nephrons and has a short loop of henle, where the majority of the tubule is located in the renal cortex Juxtamedullary Nephrons  - 15% of all nephrons - longer loop of henle that goes further down into the renal medulla. - These nephrons help maintain a salty gradient in the medulla and help us to maintain as much water and salt as possible - When naming the peritubular capillaries that surround these type of nephrons, it's important to note that they are called the vasa recta - these nephrons do still have peritubular capillaries around the convoluted tubules, however, the network of capillaries that surround the long loop of henle is called the Vasa Recta Basic Renal Processes Three basic processes involved in urine formation 1. Glomerular Filtration 2. Tubular Reabsorption 3. Tubular Secretion 1. Glomerular Filtration - first step in urine formation - the glomerulus is made up of the glomerulus capillaries - We start by pushing out the smaller components of the blood plasma out of the glomerulus capillaries, so that the cup of the bowman’s capsule can catch it. - H2O, Smaller Ions like Na+, K+, Cl-, and smaller waste products are being filtered out - things that are being left behind so that they could continue down the efferent arteriole, are RBC and proteins of that size 2. Tubular Reabsorption - As filtrate flows through the rest of the tubule, substances of value to body are returned to the peritubular capillary plasma - tubular reabsorption is the process in which when something in the tubule will be moved back into the bloodstream via the peritubular capillaries - This process is selective movement. 3. Tubular Secretion - the selective transfer from the bloodstream of the peritubular capillaries back into the tubular lumen.  - The first route of filtration was glomerular filtration. Tubular secretion would be the second route Glomerulus Filtration - the glomerular capillaries has fenestrations that allows for the waste products to escape from the bloodstream - The basement membrane is directly outside the blood cell - The podocytes sit on top of the capillaries that have spaces in between them in order to help make the smaller waste products be filtered out - The basement membrane helps to create a bridge between the glomerular capillary and bowman’s capsule - the filtration slits are made with the space in between the podocytes, these slits are on the opposite side of the fenestrations located on the glomerular capillary Passes through the filter: - water, electrolytes, glucose, amino acids, fatty acids, vitamins, urea, uric acid, creatinine What’s the motivation to be pushed into Bowman’s Capsule? 1. Glomerular Capillary Pressure - pressure exerted by the blood in the glomerular capillaries, usually at 55 mmHg at rest - this is the driving force that’s actually pushing this products out of the glomerulus capillaries and into bowman’s capsule 2. Plasma-colloid osmotic pressure - Water that is being pushed out from the capillary, creates a pressure gradient because of the rules of osmosis where water wants to go BACK to where all the big proteins are at. - This pressure is typically 30 mmHg 3. Bowman’s Capsule Hydrostatic Pressure - because of the filtration, bowman’s capsule begins to get full, creating a pushback, and pressure that opposes filtration - Usually 15 mmHg What’s the net pressure of these three processes ?  - Glomerular Capillary Pressure sits at 55 mmHg and is the only one that favors filtration, and the sum of the other two processes that oppose filtration is 45 mmHg creating a net pressure of +10 mmHg in favor to filtration Glomerular Filtration Rate - the rate at which your blood is filtered each minute in the glomerulus - This rate is dependent on the glomerular capillary blood pressure **the kidneys can adjust the glomerular filtration rate at any time - GFR control is achieved by two homeostatic mechanisms, Renal Autoregulation and Hormonal Control Glomerular Filtration when you constrict the afferent arteriole diameter: decrease resistance: increases blood flow: decreases Glomerulus Capillary BP: decreases GFR:decreases when you dilate the afferent arteriole diameter: increases resistance: decreases blood flow: increases Glomerulus Capillary BP: increases GFR:increases Overview of Urine Formation 99% of filtered Na+ is reabsorbed after being pushed out via glomerular filtration - 67% reabsorbed in the PCT - 25% is reabsorbed in the loop of Henle - 8% is reabsorbed in the DCT and Collecting Duct 80% of filtered H2O is reabsorbed back after glomerular filtration - 65% is reabsorbed in the PCT - 15% is reabsorbed in the loop of Henle Reabsorption in the Proximal convoluted tubule - the reabsorption process takes place in the epithelial cells of the PCT - the epithelial cells has GLUT transporter, a Na+-H+ antiport, a Na+/K+ pump, Cl- antiport, K+-Cl- symport, and aquaporins - Another way to reabsorb in the PCT is via Paracellular Transport, which happens in between the cells of the epithelial. Some items include, ions, water, and uric acid Tubular Secretion in the PCT - the removal of waste products in the peritubular capillaries back into the PCT. - waste products include urea, uric acid, ammonia, and a little creatinine - this process helps to clear blood of pollutants, morphine, penicillin, aspirin, and other drugs The Loop of Henle - remember we are working with juxtamedullary nephrons in this process - the goal of the loop of henle is to generate a saline gradient that conserves water and concentrates the urine - when the filtrate first enters the loop of henle is has a concentration of 300 milli osmoles/ the descending limb of the loop of henle is only permeable to water and while the renal medulla is very salty, therefore water will leave the descending limb only leaving behind salt and a lot of waste - As the filtrate travels through the descending limb, grows in concentration reaching a 1200 milliosmoles before approaching the ascending limb of the loop - the ascending limb is only permeable to the ions Na+ and Cl- and those ions will leave the filtrate, helping the filtrate become less concentrated, having a concentration of around 100 milliosmoles when leaving the ascending limb of the loop of henle - Countercurrent multiplication is the process in which a vertical osmotic gradient in the renal medulla enables H2O and NaCl to be reabsorbed from the filtrate and thus creating the concentrated urine Countercurrent Multiplication  - according to countercurrent multiplication, it states that the filtrate goes down the descending limb of the loop is become more concentrated because water is moving out of the limb because of osmosis - As the filtrate comes back up the ascending limb of the loop, it wants to create a 200 milliosmoles different between the interstitial fluid of the renal medulla and itself - along the ascending limb we will find a lot of Na/Cl/K transporters, NaCl gets pushed out to the vasa recta and enters K, until the filtrate has a 200 milliosmoles different between the interstitial fluid of the renal medulla - as the filtrate goes further up the ascending limb, it leaves behind urine with not as much salt in it but only waste products. The DCT and Collecting Duct - fluid arriving in the DCT still contains about 20% of the H2O and 7% of the NaCl from the glomerular filtrate - the filtrate still isn’t completely ready to be urine because it contains the 20% of the H2O and 7% of the NaCl from the glomerular filtrate, and would result in urinating 36 liters of fluid a day - The DCT and Collecting Duct secrete H+ and K+ pushing it into the tubule to then be excreted out as urine, and also will reabsorb amounts of H2O and NaCl Aldosterone - the salt retaining hormone that is a steroid secreted by the adrenal cortex when blood Na+ concentration drops or when K+ concentration rises - aldosterone helps to motivate Na+ out of the tubule and back into the peritubular capillary and pushes out the K+ back into the filtrate. - Aldosterone inserts more Na+K+ pumps into the principal cells of the DCT and CD in order for the Na+ concentration to fall in the filtrate Outcome of Aldosterone - Stimulates the kidney to reabsorb more Na+ and secrete K+, where H2O and Cl- will passively follow Na+ as a consequence - The outcome of reabsorbing more Na+ and H2O into the capillary means that blood pressure goes up, and blood volume increases,and urination will lessen Antidiuretic Hormone / Vasopressin - make just the CT more permeable to H2O by inserting more aquaporins into the epithelial cell lining in the CD therefore making the CD more permeable to H2O - This hormone is produced by a neuron in the hypothalamus,by the supraoptic neuron, then released into the posterior pituitary gland, and therefore into the general circulation  - this hormone is released in response to dehydration and rising blood osmolarity Atrial Natriuretic Peptide (ANP) - this hormone is produced by the myocardium of the heart and is released in response to high blood pressure Four Outcomes of ANP - dilates the afferent arteriole and constricts efferent arteriole therefore increasing GFR - inhibits renin and aldosterone secretion - inhibits Anitdiuretic hormone - Inhibits NaCl Reabsorption by the collecting duct because water follows Na Renal Autoregulation of GFR - renal Autoregulation is the ability of a nephron to adjust their own blood flow and GFR without external (nervous or hormonal) control - it follows two methods, myogenic mechanism, and tubuloglomerular feedback Myogenic Mechanism - the inherent of smooth muscle to contract when stretched - the process where the arteriole expands due to high blood pressure but constricts soon after to prevent blood flow into the glomerulus doesn’t change to much, the opposite is valid as well - its a homeostatic mechanism that tries to regulate a normal amount of blood flow through the afferent arteriole Renal Autoregulation of the GFR - the DCT is in direct communication with Bowman's capsule, and creates this communication line because of the juxtaglomerular apparatus cells in the DCT communicating with glomerulus about how much the amount of filtrate is leave the tubular component of the nephron Macula Densa - patch of closely spaced epithelial cells at the end of the nephron loop on the tubules facing the arterioles - one of the specialized cells of the juxtaglomerular apparatus - They form the part of wall of the DCT and monitor the filtrate about how concentrated it is and will communicate with the glomerulus Juxtaglomerular cells/ Granular Cells - enlarged smooth muscle cells in the afferent arteriole directly across from the macula densa cells that receive the signal from the macula densa cell when something is off about the filtrate - also contains the hormone renin Mesangial cells - found between the glomerular capillaries - they control the diameter of the glomerular capillaries Juxtaglomerular Apparatus When the GFR is too high - our urine will have too much water and NaCl tan normal - the macula densa will stimulate the juxtaglomerular cells to contract, which will constrict the afferent arteriole, reducing the GFR to normal When the GFR is too low - our urine will have little to no water, NaCl, or no waste - Macula Densa will relax and also relax the afferent arteriole and mesangial cells which will increase blood flow and GFR