so welcome to chapter 26 the urinary system Sorry that was silly I know Anyway so um this is going to be another long um lecture Um not because it has a lot of organs because it it really has only two main organs the kidney and the bladder However there's a lot of processes that you have to kind of get used to You'll talk more about it during um physiology So I'm just hanging there But there's a lot of tubes and a lot of ducks and a lot of uh reasons why these tubes and ducks are like that So um there's a lot of cell types So hang in there And you know uh sometimes I tend to talk a little slowly when I do my lectures Okay So ask questions Um make sure you get in contact with me if you need help and I'll see you later, enjoy! To begin let's identify the major organs that comprise comprise the urinary system As you can see here the primary warhorse are the kidneys We have two the right and the left kidney situated here in the posterior abdominal cavity Their principal function is to produce urine a liquid waste produ product containing various metabolic byproducts Next we have the uretors These are muscular tubes one extending from the from each kidney responsible for transporting the urine that is continuously produced in the kidneys down the urinary bladder The urinary bladder are located is located the urinary bladder is located in the pelvic cavity is a distensible muscular sack that serves as a temporal storage reservoir for urine Its ability to expand allows us to control the frequency of urination Finally urin urine is eliminated from the body through the urethra This is a single tube that extends from the bladder to the external environment It is important to note that in males the urethra also serves as a passageway for semen during reproduction We also have several related structures that are crucial for the function or proximity of the urinary system Superior to each kidney sits the adrenal gland An endocrine gland we discussed already While not directly part of the urinary system it plays a role in regulating fluid balance and blood pressure which indirectly impacts the kidney's function The renal artery and renal vein are the major blood vessels directly serving each kidney The renal artery branching from the aorta delivers oxygenated oxygenated blood containing waste products to the kidney for filtration The filtered blood then exits the kidney via the renal vein which drains into the inferior vennea for return to the heart So now let's move beyond the simple production and elimination of urine and dive into the crucial roles of the urinary system They play a crucial role in maintaining the overall bodily homeostasis It is not just about waste removal It is a multifaceted system with several vital functions We can characterize this into four We can categorize these into four main areas The main functions are the following Excretion of metabolic waste regulation of water salt balance regulation of asset base balance and secretion of hormones in the excretion of metabolic waste We already have talked about a little bit about this but this is a primary function of the urinary system The urinary system filters waste products generated by our body's metabolic processes from the blood and eliminates them in urine We'll discuss a specific examples very shortly We also use the urinary system for regulation of water salt balance also known as the fluid and electrolyte balance The kidneys play a critical role in maintaining the correct balance of water and electrolytes like sodium potassium and chloride in our body in a in our body fluids They achieve this by adjusting the amount of water and these ions that are reabsorbed back into the blood or excreted in the urine In other words if you have too much water you will eliminate the water If you have too much ions you will eliminate the ions This is essential for maintaining blood volume blood pressure and proper cellular function Regulation of acid base balance or pH homeostasis The kidneys are also vital in maintaining the pH balance of the blood They can excrete excess acids or bases and regulate the concentration of bicarbonate ions a key buffer in the blood This is this precise control is crucial for the proper functioning of enzymes and other physiological processes Secretion of hormones The kidneys are endocrine organs themselves meaning that they produce and secrete hormones that have systemic effects Key hormones produced by kidneys include eriththropoine EPO which stimulates red blood cell production in the bone marrow and renine an enzyme that initiates the renin andostens and dorserone system a crucial pathway for regulating blood pressure and fluid balance The kidneys also play a role in activating vitamin D So as you can see the urinary system is far more than just a waste disposal system It is a crucial regulator of our internal environment Let's now go a little deeper into the first of these functions the excretion of metabolic waste Our bodies constantly generate waste products as a result of normal metabolic activities URA is a primary nitrogenous waste product in humans resulting from the breakdown of amino acids in the liver During protein metabolism amino amino groups which contain an NH2 are removed and converted to ammonia which is highly toxic The liver cleverly converts this ammonia into a less toxic substance ura through the ura cycle URA is the is then transported into the blood to the kidneys for excretion in urine It is crucial to understand that clinical significance of this process If the kidneys are not functioning properly ura can accumulate in the blood a condition known as uria or esotia As you mentioned ureia can lead to a range of serious symptoms including arrhythmias vomiting and respiratory distress and if left untreated it can indeed be fatal This highlights the critical role of the kidneys in maintaining safe levels of metabolic products of metabolic byproducts in our system Dialysis is a lifesaving treatment for individuals with kidney failure that mimics the filtration function of healthy kidneys Creatine is another important metabolic waste product This is a byproduct of breaking down creatine phosphate a high energy molecule found in muscular tissue The rate of creat creatine production is relatively constant and proportional to muscle mass For this reason creatine level in levels in the blood are often used as a clinical indicator of kidney function Elevated creatine levels can suggest impaired kidney filtration Finally we have uric acid which is a waste product resulting from the breakdown of nucleotides the building blocks of DNA and RNA Uric acid has limited sol solubility in water When there is an over production or under excretion of uric acid its concentration in the blood can rise leading to the formation of uric acid crystals These crystals can precipitate in various tissues most commonly in the joints causing a painful inflammatory condition known as gout Gout attacks are characterized by intense pain redness and swelling in the affected joints often in the big toe Understanding the nature and origin of these metabolic waste underscores the importance of the kidneys in their efficient removal preventing the buildup of toxic substances that can severely compromise our health The next critical function of the urinary system is the regulation of blood composition which encomp encompasses several vital homoatic mechanisms Regulation of water salt balance or fluid electrolyte balance and maintaining acid base balance or pHostasis in regulation of the water salt balance The kidneys play a central role in maintaining the delicate balance of water and electrolytes particularly sodium and potassium in our blood This regulation is essential for maintaining blood volume and consequ conse and consequentially blood pressure The concentration of solutes such as sodium in the blood significantly influences the movement of water via osmosis For example increased sodium retention leads to increased water retention thereby increasing blood volume because the circulatory system has a limited capacity This increased blood volume contributes to higher blood pressure The kidneys precisely control the levels of sodium and potassium ions in the blood through the process of filtration reabsorption and secretion which will ex which we will explore in more detail in human physiology Hormones like ADH and aldoststerone while acting on the kidneys They are key players in this integrate regulatory process Regulation of acid base balance or pH home homoasis The maintain that the maintenance of blood pH within a narrow range around 7.4 is crucial for the proper functioning of enzymes and other physiological processes The kidneys are instrumental in this by regulating the concentration of hydrogen ions and bicarbonate ions in the blood If the blood becomes too acidic low pH the kidneys can excrete more hydrogen ions into the urine and reabsorb more bicarbonate ions Remember bicarbonate is a key blood buffer This will be back into the bloodstream does raising the pH Conversely if the blood becomes too alkaline or high pH the kidneys can retain hydrogen ions and excrete more bicarbonate ions The incred incret in intricate mechanisms underlying this assetbased balance will be a significant topic in your study of human physiology Beyond its role in waste excretion and blood composition regulation the kidneys also function as endocrine glands secretreting important hormones that have systemic effects Some of these hormones are calcitriin and renin The kidneys play the final step in the activation of vitamin D The precursor to vitamin E I mean D sorry The precursor to vitamin D is either ingested or synthesized in the skin through sunlight exposure It then undergoes initial processing in the liver before being converted by the kidneys into the active form calcitrial Calcitriol is crucial for increasing calcium absorption in the small intestine which is vital for bone health nerve function and muscle contraction Edithropoin or EPO as the name suggests ediththropoin is a hormone secreted by the kidneys in response to low oxygen levels in the blood hypoxia EPO travels to the bone marrow and stimulates ediththropoesis the production of red blood cells This increased red blood cell production enhances the oxygen carrying capacity of the blood thereby resolving hypoxia Renin the kidneys secrete the enzyme renin in response to low blood pressure or low blood volume Renin initiates the renin angioensin aldosttoterone system or RAS R A S a complex hormonal cascade that ultimately leads to the constriction of blood vessels and the retention of sodium and water by the kidneys stimulated by alderes from the adrenal glands This system plays a critical role in regulating blood pressure and fluid balance in the body Therefore the kidneys are not only filters and regulators but also important contributors to hormonal control within the body Now let's discuss anatomical location of these vital organs The kidneys are described as being retroparonium meaning they are located behind the paronium The ceros membrane lining the abdominal cavity As you can see in this posterior view they are situated against the posterior abdominal wall beneath the rib cage for some protection The superior view of a cross-section further illustrates the retroparitinal's position with the kidneys located posterior to the digestive organs within the peritonial cavity It is also important to note that the slight difference in the vertical position As you can see the left kidney is typically situated slightly superior or higher to the right kidney This is primarily due to the presence of the liver a large organ located in the upper right quadrant of the abdomen which occupies space and displaces the right kidney slightly inferiorly Finally recall that we discussed the adrenal glands earlier These endocrine glands are located on the superior surface of each kidney like caps sitting on top of them Now let's dive into the gross anatomy of the macroscopic structures of the kidney And yes I said macro A typical adult kidney is approximately 10 cm long and 5 cm wide and 2 cm thick Roughly the side the size of a bar of soap If we examine the kidney surface we observe a prominent indentation on its medial side called the helium This helium is the point of entry and exit for several crucial structures much like the helium we saw in the lymph nodes and lungs Specifically the renal artery enters here bringing blood to be filtered The renal vein exits carrying filtered blood away and the uretor also emerges from the helum transporting ur urine urine Additionally nerves and lymphatic vessels pass through this region Superficial to the kidney tissue itself is a tough fibrous outer layer called the renal capsule This capsule provides a protective barrier against trauma and infection and it helps the kidney maintain its characteristic shape Moving internally we can see distinct regions like the outer renal cortex and a deeper renal medula The renal cortex is the more superficial region while the renal medula lies deep to it While we dive into the microcopic structure later it is helpful to know that the cortex is primarily where the initial filtration of blood occurs and the medula is crucial for concentrating urine urine Within the medula you'll observe several triangular or cone-shaped structures called renal pyramids The base of each pyramid faces the cortex and the pointed up apex called the renal papilla projects towards the center of the kidney It is at the renal papilla that urine is released from the collecting dots Separating these renal pyramids are inward extensions of the renal cortex called renal columns These columns contain blood vessels and connective tissue that support the kidney's structure As urine is produced within the nephrons or nephrons located in both the cortex and medula it flows through collecting ducts that open at the renal papilla From the papilla the urine drains into cuplike structures called minor calluses Several minor calluses then merge to form large major calluses Finally all the major calluses drain into a funnel shaped region called the renal pelvis The renal pelvis is continuous with the uretor the tube that carries urine to the urinary bladder Now looking at this dissected kidney we can appreciate these same regions in a renal specimen You can clearly see the outer cortex the darker estriated pyramids of the medula the renal columns extending between them and how the tip of a papila drains into a minor callex which then joins a major callex ultimately leading to the renal pelvis Finally let's define a renal lobe A renal lobe consists of a single renal pyramid the portion of the renal cortex that lies superficial to that pyramid and the adjacent renal column on either side Understanding the concept of a renal lobe is particularly helpful when we discuss the organization of blood supply within the kidney as the interlo arteries run between these loes This understanding of the kidneys lower structure is essential when we trace the path of blood supply The renal artery a branch of the abdominal aorta enters the kidney at the helum The first major branch of the renal artery within the kidney is the segmental artery These segmental arteries then further subdivide into interlo arteries As the name suggests inter between lowar loes These arteries travel within the renal columns passing between the renal pyramids and therefore between the renal loes towards the cortex Continuing our exploration of the kidney's gross anatomy let's now trace the detailed pathway of blood flow As the interlo arteries ascend within the renal columns they reach the cortic medularary junction the boundary between the cortex and the medula Here the interlobal arteries branch to form the arquate arteries The term arquate means bow shape And these arteries arch over the base of the renal pyramids running along this cortimed junction Branching off the arquate arteries and radiating outwards into the renal cortex are the cortical radiate arteries sometimes also called the interlobular arteries though distinct from the interlo arteries between loes Their name reflects the radial course through the cortical region extending away from the pyramids The cortical the cortical radiate arteries then give rise to the aphrine arterials Each aphrine arterial supplies blood to a single glomeus a specialized capillary network where the process of blood filtration begins Blood enters the glomemeulus via the aphrine arterial passes through the capillary network and then exits through the apherant arterial The aphrine arterial then leads to a network of capillaries surrounding the renal tube tubules in the cortex This is called the peritubular capillaries These capillaries are crucial for the reabsorption of essential substances and the secretion of waste products between the renal tubules and the blood In nephrons with long loops of henley extending into the mod medula the epherent arterials give rise to the specialized capillaries called the vaserecta which run parallel to these loops and play a v a vital role in concentrating urine The Henley the loops of Henley extending to the medularary are also called the juga medularary nephrons Blood then flows from the peritubular capillaries into the venules which are small veins These venules then drain into the cortical radiate veins As their name suggests these veins run parallel to the cortical radiate arteries From the cortical radiate veins blood flows into the aruate veins These veins follow the small arching path as the alurate arteries curving over the renal pyramids at the cortical medularary junction The arquate veins then drain into the interlobal veins which travel between the renal loes within the renal columns It is important to remember that the ephrine arterial peritubular capillaries and venules while not always clearly depicted on simplified diagrams of the gross blood supply are essential components of the renal microirculation within the cortex In the case of the vaserecta the medula from the interlobber veins Blood then flows directly into the renal vein As we can see illustrated here the interlobal veins converge and empty into this large vessel A significant difference to note between the arterial and venos pathways is the absence of the segmental veins The renal vein then exits the kidney at the helum and drains directly into the inferior venneva carrying the filtrated blood away from the kidney and back to the systemic circulation Now that we have explored the gross anatomy and blood supply of the kidney and the blood circulation in the kidney let's focus on the nephron or nephron which is the structural and functional unit of the kidney Think of the nephron as the microscopic machinery responsible for actually filtrating blood and producing urine Each kidney contains approximately 1 million of these intricate units While the nephron has several distinctive parts we can broadly divide it into two main components the renal corpus skull and the renal tubule The renal corpus skull is located in the renal cortex and consists of two key structures The glomeular capsule also known as the bowman's capsule This is a C-shaped structure that surrounds the glomeilus and the glomeilus which is a capillary network receiving blood from the apherant arterial that we have discussed earlier Blood is filtrated from the glomeular capillaries into the space within the bowsman capsule The second main part of the nephron is the renal tubule a continuous series of tubes that extends from the bowman's capsule and is responsible for further processing the filtrated fluid now called filtrate to ultimately form urine The different segments of the renal tubule in the order that filtrate passes through them are the proximal convoluted tubule or PCT a highly coiled segment located in the cortex immediately extending from the bowman's capsule its convoluted nature increases its surface area for reabsorption Then we have the nephron loop also known as the loop of henley which extends from the proximal convoluted tubule into the renal medula and then back to the cortex It has a descending limb and an ascending limb and plays a critical role in concentrating urine Then you have the distal convoluted tubio or DT DCT distal convoluted tubio which is another coil segment located in the cortex distal to the loop of Henley It is involved in further reabsorption and secretion Finally the collecting duct while several nephrons drain into a single collecting duct It plays a crucial role in the final concentration of urine and is influenced by hormones like ADH Collecting docks eventually merge and empty into the minor calluses Let's begin our detailed look at the nephron Starting with the renal corpus This is where the crucial process of blood filtration takes place Blood enters the glomeallo via the aerant arterial flows through the glomeular capillaries and exits via the epherent arterial due to high pressure and the specialized filtration membrane which is composed of the fenestrated glomeallo endothelio The fused basement membrane and the podocytes with their filtration slits Fluid and a small solutes are forced from the blood into the space within the glomeular capsule also known as the bowman's capsule This fluid now is called the glomemer filtrate is similar in composition to blood plasma but lacks large proteins The glomeular capsule itself is lined with a simple esquamos epithelium The glmoral capillaries are surrounded by a specialized cells called podocytes whose foodike processes interlink to create filtration slits These slits along with the other layers of the filtration membrane precisely regulate what passes from the blood into the glumber capsule In essence the renal corps acts as a highly efficient filter separating water and a small solutes from the blood The glomemeal filtrate now within the bowman's capsule immediately enters the proximal convulated tubule This segment is characterized by its simple cubial epithelium with a prominent brush border on its aical surface Apical surface is also known as the luminal surface This brush burder is formed by a dense layer of microbilly dramatically increasing the surface area available for reabsorption The proximal convoluted tubule is a major site of reabsorption reclaiming essential substances from the filtrate back into the blood within the peritubular capillaries These small molecules include water ions including sodium potassium chloride and bicarbonate organic nutrients like glucose and amino acids and any small plasma proteins The filtration is done through active and passive transport The filtration goes out to of the tubular fluid and into the surrounding interstitial fluid eventually entering the peritubular capillaries The cubial cells with their extensive microa are numerous and numerous mitochondria are structurally well adapted for this high level of reabsor reabsorptive activity The reason why you have numerous mitochondrias in these cells is for the is to make the energy to drive the active transport hisystologically the proximal convoluted tubule is identifiable by these cubial cells and the darkly stained aical stro surface representing the dense brush border The filtrate then flows into the nephron loop also known as the loop of Henley This U-shaped structure has two main limbs a descending limb that travels from the cortex into the medula and an ascending limb that returns to the cortex The walls of the loop of Henley exhibit different epithelial types as along its length reflecting their distinct functions The thin descending limb is lined with simple esquamos epithelium which is highly permeable to water As the filtrate descends into the hyper As the filtrate descends into the hyperosmotic environment of the renal medula water is passively reabsorbed from the tubular fluid into the surrounding interstatial fluid further concentrating the filtrate The thick ascending limb in contrast is lined with kuboreal epithelium which is impermeable to water but actively transports salts primarily sodium and chloride out of the tubular fluid and into the insertial fluid This active transport of solutes contributes to the establishment of the osmotic gradient in the medula a crucial mechanism of the kidney's ability to concentrate urine which we will discuss in more detail later Histologically the thick ascending limb is characterized by the by its cubial cells while the thin descending limb appears as a thin wall tube with simple esquamos cells Following the ascending limb of the loop of Henley the filtrate enters the distal convoluted tubule located in the renal cortex The cells lining the distal convoluted tubule are simple cubial epithelium similar in shape to those in the posterior Sorry Similar to those in the proximal convoluted tubule but they lack the prominent brush border on their apical surface The distal convoluted tubule is involved in further reabsorption of water sodium and calcium ions But unlike the proximal convoluted tubule this reabsorption is largely under hormonal control Aldoone secreted by the adrenal cortex increases sodium and water reabsorption in the distal convoluted tubule and also in the collecting duct Parathyroid hormone regulates the reabsorption of calcium in the distal convoluted tubule After the distal convoluted tubule the filtrate enters the collecting ducts and tubules which are the final segments of the nephron's collecting system These structures are also lined with simple cubal epithelium which may transition to columnar epithelium in the larger ducts closer to the renal pelvis As you can see in this image a collecting duct is a relatively large tube line with this hubial cells The collecting duct plays a crucial role in the final concentration of urine They are permeable to water and their permeability is regulated by antiduretic hormone As the collecting duct pass through the hyper hyperosmotic environment of the renal medula water can be reabsorbed resulting in a more concentrated urine It is important to note that multiple nephrons drain into a single collecting duct and these collecting dots converge as they descend deeper into the medula eventually emptying into the m minor calluses at the renal papilla Let's discuss these fundamental processes involved in urine formation There are three main steps Glular filtration tubular reabsorption and tubular secretion Glar filtration is initial step occurring exclusively in the renal corpsicle Blood enters the glomeulus under high hydrostatic pressure forcing water and small solutes across the filtration membrane and into the bo bowman's capsule forming the glumeular filtrate The composition of the filtrate is similar to plasma but lacks significant amounts of proteins The rate of filtration is heavily influenced by factors such as blood volume and blood pressure Then we have the tubular reabsorption which is the process by which the body reclaims essential molecules from the glomeular filtrate and returns them to the blood in a peritubular capillary and vaserecta Reabsorption is highly selective Reabsorption is a highly selective process ensuring the substances like water glucose amino acids and necessary ions are not lost in the urine While reabsorption occurs along the entire renal tubule and collecting duct it is most extensive in the proximal convoluted tubio Tubular secretion is a last step This process involves the movement of additional substances from the blood in the peri tubular capillaries and vaserecta into the renal tubule Secretion is a mechanism for further eliminating waste that were not initially filtrated or for regulating blood composition Significant secretion occurs in the distal dist distal convoluted tubio but it can also take place in a lesser extent in the proximal convoluted tubio and collecting ducts Examples of substances actively secreted include certain drugs hydrogen ions for pH regulation potassium ions and creatinine Once urine is formed in the nephrons and collected in the renal pelvis of each kidney it needs to be transported out of the body The first structures involved in the transportation of urine to the outside are the uretors Make sure you pay attention of how this is written U R E T E R S These are paired fibrouscular tubes approximately 25 to 30 cm long that is about 10 to 12 in This exits each kidney at the helum and extend inferiorly to the urinary bladder As you can see in these diagrams for both males and females the left and right urittors descend and connect to the posterior aspect of the urinary bladder In females the bladder is inferior and slightly anterior to the uterus Urine is propelled through the uretors towards the urinary bladder by rhythmic wavelike muscular contractions called peristas aided by gravity In this picture you see a colorized X-ray which provides a visual representation of the urinary tract The patient has received an intervenous injection of a contrast dye that is filtrated by the by the kidneys and concentrates in the urine allowing us to trace its path As you can see urine is formed within the nephrons and drain into the collecting ducts which then empty which then empties into the renal papilla located at the tips of the renal pyramids From the renal papilla the urine flows into the minor calluses several of which merge to form major calluses The major calluses then join to create the renal pelvis The funnel shaped region within the kidney From the renal pelvis the urine is transported out of the kidney via the uretor traveling down to the urinary bladder for temporary storage This type of imaging called an intravenous pyoggram or IVP can be a valuable tool in diagnosing blockage or other abnormalities within the urinary system The urinary bladder serves as a temporary storage of the urine The uretors enter the urinary bladder through the ureiteral orififices which are located in a triangular region on the posterior inferior wall of the bladder known as the trigon The trigon is clinically significant as it is a common site for persistent urinary tract infections As the bladder fills with urine the increased pressure within the bladder compresses the distal ends of the uretors effectively squeezing the uretor's orififices shut and preventing the backflow of urine into the uretors The wall of the urinary bladder is composed of a smooth muscle layer called the the trusor muscle This muscle consists of three interwoven layers of a smooth muscle fibers and its powerful construction in all directions help to effectively expel urine At the junction where the bladder narrows to become the urethra there is a thickening of the distrusor muscle forming the internal urethral sphincter This sphincter is composed of a smooth muscle and is under involuntary control Meaning we do not conscientiously control its contraction or relaxation The urethra is a tube that transports urine from the urinary bladder to the outside of the body This is why I mentioned to pay a close look to how you spell ure because it sounds a lot like urethra So do not confuse those two terms There is a significant difference in length between the female and male urethra In females the urethra is relatively short approximately 4 cm long or 1.5 in and it extends from the bladder to the external urethral orifice anterior to the vaginal opening This shorter length contributes to a high to a higher suscept susceptibility to urinary tract infections in females In males the ureizra is considerably longer about 20 cm or 8 in and it serves as dual function transporting both urine and semen It passes through the prostate gland and eurogenital diaphragm and then extends through the penis to the external urethral orifice The internal urethar sphincter which we just discussed is located at the bladder urethra junction Inferior to this is the external urethral sphincter This sphincter surrounds the urethra Now I just gave you a lot of information between males and females But remember this is a biological male and a biological female The external urethral sphincter unlike its internal counterpart is composed of a skeletal muscle specifically within the eurogenital diaphragm This means it is under voluntary control We learn to control the contraction and relaxation of this sphincter during toilet training in early childhood allowing us to conscientiously control the initiation and sessation of urination As we age or in cases of certain neurological conditions such as spinal cord injuries or following events like childbirth that can weaken the pelvic floor or the I should say which weaken the pelvic floor muscles The voluntary control over the external urethral espinter can be compromised potentially leading to urinary incontinents The body employs simple urinary reflexes to regulate the storage and voiding of urine The urinary storage reflex is active when the bladder is feeling but not yet significantly stretched Sensory receptors in the bladder wall detect the increasing volume leading to increased sympathetic nervous system activity This sympathetic stimulation has two main effects One it inhibits the the trusor muscle by preventing it from contracting and expelling urine prematurely The second effect is the stimulation of the contraction of both the internal urethral sphincter and the external urethral sphincter further ensuring that the urethra remains closed and preventing any leakage of urine from both bladders The overall goal of the urinary storage reflex is to maintain continents as a bladder gradually fills The urinary avoiding reflex also known as urination or mur muriation is triggered when a stretch receptors in the bladder wall are activated by a significant increase in bladder volume This activation initiates a stretch activated spinal reflex The parasympathetic nervous system is stimulated leading to contraction of the the tors muscle and relaxation of the internal urethral sphincter The contraction of the detr muscle involves the smooth muscle of the bladder walls which increases pressure within the bladder The reflection of the internal urethral sphincter is due to the inhibition of the sympathetic stimulation While these initial steps are reflexive the external urethral sphincter being under voluntary control requires conscious relaxation for urination to occur The cerebral cortex plays a role in overriding or facilitating this reflex allowing us to control the timing of urination Neurological conditions that disturb the nerve pathways involved in the reflex can lead to the condition known as neurogenic bladder characterized by impaired bladder emptying or incontinents In a personal note it is amazing to see all the structures that are needed for proper bladder control When I injure my back a few months ago and went to the doctor one of the first questions a doctor asked was if I could control my urination And if you think about it the reason why they asked this is to measure the level of a spinal injury Because if you have a spinal injury grave enough to stop the voluntary control of your bladder then something really bad is happening But if your bladder control stays normal then the injury may be not as severe As we age the urinary system undergoes several structural and functional changes One significant change is a decrease in the number of functional nephrons Studies indicate a decline of approximately 30 to 40% in the number of nephrons between the ages of 25 and 85 This reduction in the kidneys functional units directly translates to a less efficient filtration system of the blood Furthermore the glomeular filtration rate a measure of how well the remaining nephrons are functioning also tends to decline with age This can be due to a structural changes within the glomei such as thickening of the glomeular basement membrane and glomeallo chlorosis Age related changes also affect muriation control or urination control The urethral sphincters can lose muscle tone particularly the external urethral sphiner leading to incontinence The involuntary loss of bladder control This can manifest as a slow leak of urine or a sudden urge with a inability to re to reach a toilet in time Neurological conditions affecting the central nervous system such as a stroke Alzheimer's disease and other central nervous system disorders can impair the neural pathways involved in bladder control leading to a inability to conscientiously regulate muration In males benign prostatic hyperplasia or non-cancerous enlargement of the prostate gland is a common age related issue As you remember from a previous slide the prostate gland surrounds the urethra just inferior to the bladder When the prostate enlarges it physically compresses the urethra increasing resistance to urinary flow and reducing urine flow This urine retention creates an a stagnant environment in the bladder significantly increasing the risk of urinary tract infections All right So that was the end of chapter 26 the urinary system I hope you learned a lot Um next chapter is going to be the reproduct reproductive system uh specifically the male So uh again if you have any questions let me know You can always watch this video again and again as many times you as you can as many times as you want as fast as you want Um just make sure that um you let me know if you have any questions See you later