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HA&PII Urinary System Weekly Notes

by: Victoria Hills

HA&PII Urinary System Weekly Notes Biol 2230-001

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Victoria Hills
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Here are all the notes from the slides of the Urinary System powerpoint.
Human Anatomy & Physiology II
Dr. John Cummings
Class Notes
Human, anatomy, Physiology, two, 2, II, Urinary, system, URINARY SYSTEM
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This 16 page Class Notes was uploaded by Victoria Hills on Friday April 22, 2016. The Class Notes belongs to Biol 2230-001 at Clemson University taught by Dr. John Cummings in Fall 2015. Since its upload, it has received 11 views. For similar materials see Human Anatomy & Physiology II in Biology at Clemson University.


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Date Created: 04/22/16
Clemson University Spring 2016 Urinary System Slide 1: Urinary System • Main focus is to filter the blood • 180 L of blood is filtered per day • In connection with other organs/systems: -­‐ Liver has a blood filtering function where it recycle old red blood cells -­‐ Lymphatic system has lymph nodes and the spleen that filters blood for the elimination of pathogens -­‐ Kidneys filter blood to get rid of metabolic wastes and maintain blood pressure, blood volume, etc. (Urinary system) Slide 2: Components of the Urinary System • (2) Kidneys: -­‐ Each has a drainage tube coming off à ureter -­‐ Ureters empty into the urinary bladder (Storage tank) -­‐ Contents of the urinary bladder will go through the urethra to be released from the body • There are no accessory structures in addition to the 4 listed components • Ureters and urethra are considered to be passage tubes • Kidneys filter the blood and get rid of metabolic wastes that pass out of the body as urine Slides 3, 4, 5, 6, 7, 8, 9, 10: Functions of the Urinary System a) Fluid Filtration: • Filtering of the blood • Movements of fluid and gradients • Passage of fluids across a filtration membrane, which is in relation to the characteristic fenestrated capillaries and pores • The liquid component of the blood (plasma) is what is filtered b) Regulate blood volume: • As filtration of the plasma occurs, it can be determined how much of the filtrate goes back into circulation in the blood stream and how much filtrate is released as urine à Allows the regulation of blood volume and therefore blood pressure of the body • The only permanent way to affect blood pressure is through the kidneys c) Maintains salt/water balance: • While filtering and regulating blood volume, salt and water balance are regulated at the same time d) Maintains acid/base balance: • While filtering and regulating blood volume, acid-base balance is regulated at the same time *Fluid filtration, regulation of blood volume, and maintenance of salt/water and acid/base balance are all very closely related to each other e) Gluconeogenesis: • Kidneys are another site of gluconeogenesis • Where amino acids and fat are able to be converted into carbohydrate derivatives to produce energy f) Renin production: • Kidneys produce renin • Associated with the renin-angiotensin mechanism that is related to water balance and blood pressure • Also a chemical that controls the activity of the kidneys g) Erythropoietin production: • Hormone secreted by the kidneys that stimulates red blood cell production in the bone marrow * Kidneys are able to regulate blood volume by the plasma and can regulate blood volume by the cellular portion of the blood h) Activates vitamin D: • The skin produces an inactive form of vitamin D that goes through sunlight and is finally activated through work in the kidney to active vitamin D Slide 11: Kidney Structure • Kidney-shaped: Has an indention on one side à Hilum • Renal artery and renal vein are located on the backside of the kidney • Renal capsule: -­‐ Very outer layer -­‐ Superficial layer that holds the kidney together • Kidney is divided into 2 regions: a) Renal cortex: Outer region -­‐ Where the functional unit of the kidney is located b) Renal medulla: Central region -­‐ Renal pelvis: o Flattened portion in the medulla connected to the ureter -­‐ Renal pyramids: o Triangular-shaped o Appear striped because they’re a collection of collecting ducts that collect filtrate from the functional units within the kidney that drain into the ureter -­‐ Renal columns: o Extensions of the cortex between the pyramids o Appear column-like -­‐ Minor calyces -­‐ Major calyces • Overall: The functional units of the kidney are located in the cortex that connect to the collecting ducts in the pyramids that empty into the minor calyces à Merge together to form the major calyces à Merge together at the renal pelvis à Everything leaves the kidney via the ureter Slide 12: Supportive Layers • Kidneys are located outside the peritoneal cavity à They are retro peritoneal • Therefore, the peritoneum isn’t what holds the kidney in place, there are other supportive layers • Renal capsule: -­‐ Holds the whole kidney together -­‐ Very outer covering • Adipose capsule: -­‐ Adipose tissue envelopes and surrounds the kidneys -­‐ Function of adipose tissue: o Act as a cushion in protecting the kidneys o Good insulator à Since a lot of blood (180 L/day) is filtered by the kidneys, much of the core body temperature that could be lost through our backs is prevented from happening • Renal fascia: -­‐ Needed since adipose tissue is a relatively weak tissue -­‐ Anchoring structure that holds the kidneys to the rear abdominal wall -­‐ AKA: A thin covering is only in the back of the abdominal cavity Slide 13: Nephron • Functional structural unit of the kidney à Each kidney has about 1 million nephrons • Glomerulus: -­‐ Branching off an arteriole à glomerulus -­‐ Special capillary bed in the kidney -­‐ Part of the nephron that consists of blood vessels (Capillary) -­‐ Fenestrated capillaries make up the glomerulus o Have pores to make them leaky o Helps in filtering the liquid portion of the blood (plasma) out à NOT cells -­‐ Capillary bed is under higher pressure than any other capillary in the body à Why many holes are needed to allow blood filtration • Renal tubule: (Tubular portion of the nephron that’s divided into segments) -­‐ Bowman’s capsule: o Ball that surrounds the glomerulus o First part of the renal tubule o Overall: Blood is delivered to the glomerulus that is under pressure à Plasma leaks out of fenestrated capillaries (But not all or else blood will stop flowing) à Collects first in Bowman’s capsule where it is then considered to be filtrate -­‐ Next, the filtrate moves from Bowman’s capsule à Proximal convoluted tubule (Close to the glomerulus)à Loop of Henle à Distal convoluted tubule (Far from the glomerulus) -­‐ Filtrate collects from the distal convoluted tubule in collecting ducts located in the renal pyramids o Single collecting ducts are able to attach to more than one renal tubule -­‐ Filtrate in the collecting ducts à ureter à urethra -­‐ Further more on Loop of Henle: o Divided into the descending limb from the proximal convoluted tubule that descends downwards towards the medulla o Ascending limb: Ascends back up to connect to the distal convoluted tubule • Renal corpuscle: Glomerulus + Bowman’s capsule together Slide 14: 2 Types of Nephrons • Cortical nephrons: -­‐ Make up most of the nephrons in the kidney, which are located in the cortex (85%) -­‐ Only a small part of the Loop of Henle descends down into the medulla • Juxtamedullary nephrons: -­‐ Make up 15% of the nephrons in the kidney -­‐ Most of the Loop of Henle is in the medulla -­‐ Loop of Henle is longer than the cortical Loop of Henle so it goes even further down into the medulla -­‐ Importance: Blood mostly goes through the cortical nephrons, but if there is a need to concentrate urine when we need more water and are dehydrated, the sphincter leading to the glomerulus à cortical nephrons can be shut off so that filtration occurs through the juxtamedullary nephrons Slide 15: Nephron Vasculature • Afferent arteriole: Blood vessel that takes blood into the glomerulus • Efferent arteriole: Blood vessel that takes blood away from the glomerulus • Efferent arteriole branches to become a regular capillary bed that surrounds the tubule that is called as the peritubular capillaries (On cortical nephrons) • Juxtamedullary nephrons the peritubular capillaries are called vasa recta (Have the same function but different names) • Process involving peritubular capillaries and vasa recta: -­‐ Blood is delivered to the glomerulus where the blood plasma leaks out of the glomerulus (Not all of it) à Blood plasma will make filtrate that fills up the cascade of tubules -­‐ 180 L of blood is processed in this manner -­‐ 99% of the fluid that leaks out of the blood as filtrate is reabsorbed back into the blood stream as it passes through the tubule -­‐ End: Fluid comes out of the tubule into the interstitial space à Peritbuluar capillaries or vasa recta • Detailed process and mechanism (Repetitive): -­‐ Blood enters the glomerulus under pressure so that the plasma leaks through the fenestrated capillaries à Collected in tubule -­‐ As the plasma (filtrate now) passes through the tubule 99% of the fluid is reabsorbed -­‐ If there are solutes and water in the Loop of Henle à They will move into the blood vessels of the 2 capillaries through the interstitial space via diffusion (Active transport) -­‐ Point of peritubular capillaries and vasa recta: Reclaim fluid that is being filtered as it moves through the tubule -­‐ The rest that is leftover in the tubule and wasn’t reclaimed à collecting duct that leaves as urine -­‐ 1.8 L of urine is produced per day Slide 16: Juxtaglomerular Apparatus • Blood comes into the glomerulus via the afferent arteriole à proximal convoluted tubule à Loop of Henle à Distal convoluted tubule à Comes back up so that is close to the afferent arteriole • At this point, there is a modification of the cells between the wall of the afferent arteriole and the wall of the distal convoluted tubule (Modification where the distal convoluted tubule runs against the afferent arteriole) • The walls of the arteriole have smooth muscle in them à Cells of the smooth muscle are where the distal convoluted tubule and afferent arteriole are in contact with one another à Smooth muscle cells (Also known as juxtaglomerular cells here- Discussed in next bullet) are able to enlarge and gain the ability to secrete renin but function as a mechanical receptor • Specifically: The kidney determines what our blood pressure is going to be through use of a mechanism (Juxtaglomerular apparatus) that measures changes in blood pressure à Juxtaglomerular cells surrounding the blood supply going to the glomerulus detect blood pressure changes à Activated to secrete renin • Renin: -­‐ Changes aldosterone production that changes the reabsorption of sodium and water -­‐ Lower blood pressure • There are also modifications in all of the distal convoluted tubules where macula densa cells are present: -­‐ Macula densa cells have chemoreceptors that work in conjunction with the mechanical receptor side of the juxtaglomerular cells -­‐ Distal convoluted tubule is ultimately going to connect to the collecting duct à Related to the concentration of the resulting filtrate as it gets ready to leave the body -­‐ If the concentration of the filtrate is changed from normal, the macula densa cells are activated à Change how the filtrate is produce by mostly activating the juxtaglomerular cells that will secrete renin • 2 ways that urine concentration is affected: -­‐ Kidney can switch from one type of nephron to another to change the concentration of urine produced -­‐ Kidney can change its activity through the juxtaglomerular apparatus to change the concentration of the filtrate produced • Purpose of changing the concentration of urine is to meet our body’s water needs à Too much water coming in will be eliminated and too little water (dehydration) will be conserved -­‐ Generally, increasing the fluid coming into our bodies increases the amount of urine produced -­‐ Generally, decreasing the fluid coming into our bodies decreases the amount of urine produced -­‐ Homeostatic process for water Slide 17: Glomerular Filtration Membrane • In the glomerulus • Fenestrated capillary has pores so that the plasma portion can pass through -­‐ Blood cells can NOT pass through -­‐ Larger molecules like proteins are able to pass through • Fenestrated capillary is surrounded by other components: a) Fenestrated epithelium: -­‐ Part of filtration membrane b) Basement membrane: -­‐ Does NOT allow large things like proteins to pass so they stay in circulation -­‐ Creates an electrically selective membrane à Charge of molecules is important as a result -­‐ Ex: Proteins have a charge and will not pass because the body does not want to lose these important hormones, enzymes, etc. c) Podocytes: -­‐ Cells with extensions called pedicels that create a filtration slits -­‐ Pedicels regulate what can be filtered by preventing filtration from happening so that some of the plasma can be kept in the capillaries to continue to circulation from the glomerulus • Water and solutes dissociated in that water (Except for large ones like plasma proteins) of the plasmas à Passes through almost all of the filtration membrane’s entirety à Bowman’s capsule à Processed in renal tubule Slide 18: Urine Formation • Process of urine production begins with filtration that occurs in the glomerulus across the filtration membrane • Filtrate contains things that the body wants to keep such as glucose or amino acids à The body retains these by taking them back out of the tubule to put back into the blood stream through the peritubular capillaries for the cortical nephrons and the vasa recta for the juxtamedullary nephrons • Overall: The blood is filtered and the good things are reabsorbed back into circulation • Substances that the body wants to get rid of such as uric acid, urea, breakdown compounds, and toxic substances with nitrate can be secreted into the tubule to be eliminated from the body as waste if they weren’t initially filtered towards the beginning of the filtration process • Some substances that did get filtered but were reabsorbed on accident during the reabsorption process can be secreted back into the tubule as well in order to get rid of them • Filtrate becomes urine, but filtrate does not equal urine • Filtrate becomes urine by taking substances out of it and adding substances to it • Filtration occurs across the glomerular capillary • Definitions: -­‐ Tubular reabsorption: o Where there is reabsorption from the tube where substances are pulled out of the tubule and put back into circulation o In short: Substances are pulled out of the tubule à Blood stream o Most occurs in the proximal convoluted tubule, but a large part of tubular reabsorption can occur in the Loop of Henle -­‐ Tubular secretion: o Substances are secreted into the tubule from the blood stream o Occurs in both the distal and proximal convoluted tubules • Overall sequence of events in urine production: Filter blood à Reabsorb wanted substances à Secrete unwanted substances à Eliminate unwanted substances Slide 19: Filtration Pressure • Glomerular filtration: -­‐ Passive filtration process that does NOT require energy -­‐ Uses pressure to push a fluid across a membrane (Filtration) to move blood into the tubule -­‐ For the most part, glomerular filtration is non-selective except for proteins • Glomerular hydrostatic pressure (Further discussed below): -­‐ AKA glomerular blood pressure -­‐ Important component in determining how much filtration occurs -­‐ Blood pressure is higher in the glomerular capillary than any other capillary bed in order to make filtration more efficient -­‐ Anything that changes blood pressure in the glomerulus will change the filtration rate o Anything that increases blood pressure will increase filtration o Anything that decreases blood pressure will decrease filtration • Tubular reabsorption (Review): -­‐ Substances are reabsorbed back into the blood stream from the tubule due to concentration gradients or hormonal control -­‐ Begins immediately as soon as the filtrate is in the proximal convoluted tubule -­‐ Glucose and amino acids are reclaimed in the filtrate -­‐ Water and ions are able to be reclaimed but they are under hormonal control due to aldosterone and ADH (Regulate water reabsorption) -­‐ 99% of water is reabsorbed -­‐ Movement of these substances will require energy in some cases (Active or passive process both occur with substances) • Tubular secretion (Review): -­‐ Unwanted substances are secreted into the tubule out of the blood plasma -­‐ Ways to eliminate form the body: o Filter substances and don’t reabsorb unwanted substances o Substances that aren’t originally filtered/reabsorbed are secreted into the tubule later in order to eliminate them -­‐ Occurs mostly in the proximal convoluted tubule -­‐ Can occur in the distal convoluted tubule and collecting ducts -­‐ Secretion occurs within the cortex of the kidney and NOT down by the medulla • Again: Hydrostatic pressure of the blood pressure in the glomerulus drives filtration + there are other factors that regulate filtration (Further discussed) • Factors that affect filtration pressure: a) Glomerulus hydrostatic pressure: -­‐ Pressure of the blood inside the glomerulus capillary -­‐ Where want to force substances out of circulation into Bowman’s capsule b) Colloid osmotic pressure of intracapsular space: -­‐ Where want to pull substances out of circulation into Bowman’s capsule -­‐ Due to large molecules, fats, and other large substances c) Colloid osmotic pressure within the glomerulus: -­‐ Resistive force that wants to prevent substances from coming out of circulation -­‐ Proteins can NOT cross into the tubule à Draws fluid back into circulation due to concentration gradient created d) Capsular hydrostatic pressure: -­‐ Resistive force that wants to prevent substances from coming out of circulation -­‐ Fluid that collects in Bowman’s capsule is pushing back on the glomerulus • Overall: These 4 factors work against each other to determine how much passes out in filtration à Changing one the factors will change the filtration rate • Net filtration is 10 mm Hg, meaning that filtrate typically moves out of circulation into Bowman’s capsule Slide 20: Renal Blood Flow (RBF) and Glomerular Filtration Rate (GFR) • Glomerular filtration rate: -­‐ Volume of filtrate formed/minute -­‐ Determined by the function of combined action of all the nephrons in both kidneys • Afferent arteriole: -­‐ Brings blood to the glomerulus -­‐ When it has changes its diameter and is able to constrict to become smaller à Less blood is delivered to the glomerulus à Reduced renal blood flow as a result à Less filtrate is formed à Ultimately have reduced filtration rate -­‐ Dilation à More blood is delivered to the glomerulus à Greater renal blood flow as a result à More filtrate is formed à Ultimately have increased filtration rate • Efferent arteriole: -­‐ Takes blood away from the glomerulus -­‐ Constriction à Less blood is able to pass out of the glomerulus à Less renal blood flow à Greater filtration due to the blood staying in the glomerulus longer so more can seep out à Increase in pressure since the blood is backed up à Ultimately have increased filtration rate -­‐ Dilation à Blood passes more rapidly- Increased renal blood flow à Not a lot of pressure à Ultimately have reduced filtration rate • Increasing filtration rate à Increased urine formation unless there is a change in the reabsorption rate that occurs somewhere else in the tubule Slide 21: Filtration Regulation • 4 different mechanisms for the regulation of filtration • Kidney prefers to have a relatively constant rate of filtration, meaning there is a homeostatic component of filtration • Generally: Water in = Water out • 2 intrinsic mechanisms of kidney filtration auto-regulation: a) Myogenic mechanism: -­‐ Involves the contraction and relaxation of smooth muscle -­‐ When smooth muscle is stretched, it contracts -­‐ Afferent arteriole side of the glomerulus: o Systemic blood pressure increases à Blood pushes more on the afferent arteriole à Smooth muscle in the afferent arteriole responds by pushing back and constricting à Less blood is delivered to the glomerulus à Reduced filtration rate o The increase in blood pressure would have caused an increased in filtration, but the kidney prefers to be at the same level of filtration as much as possible o Summary: Kidney counteracts the increase in systemic blood pressure by constricting the afferent arteriole o When systemic blood pressure decreases, the opposite occurs à Afferent arteriole dilates à Increases filtration rate o Overall a homeostatic process -­‐ *Myogenic mechanism is NOT linked to the other mechanisms b) Tubuloglomerular mechanism: -­‐ Involves action of the macula densa cells that are located in the distal convoluted tubule and is part of the juxtaglomerular apparatus -­‐ Macula densa cells have receptors that determine the osmolality of filtrate (Concentration of fluid inside the distal convoluated tubule) and can detect the amount of flow passing à These factors will effectively change the diameter of the afferent arteriole accordingly -­‐ Low osmolality: o Means that dilute urine is passing through the distal convoluted tubule o Causes vasodilation of the afferent arteriole à Increase in filtration rate o Dilute urine ultimately stimulates increased filtration -­‐ High osmolality: o Means that concentrated urine is passing through the distal convoluted tubule o Stimulates vasoconstriction of the afferent arteriole à Reduce in filtration rate o Concentrated urine ultimately stimulates reduced filtration • Connection between intrinsic and extrinsic mechanism of filtration regulation: -­‐ Macula densa cells are able to send a signal to the juxtaglomerular cells to cause them to release renin à Connection between extrinsic hormonal mechanism and tubuloglomerular intrinsic mechanism -­‐ Macula densa cells also affect aldosterone production • 2 extrinsic mechanisms that involve structures other than the kidney for filtration regulation: a) Neural: -­‐ Blood à Kidneys that process the blood continuously, but in a time of emergency, the body will send sympathetic nervous impulses to direct blood to muscles, heart, brain, etc. -­‐ This means that the neural mechanism acts as an override -­‐ Sympathetic nervous impulses ultimately affect the diameter of the afferent arteriole to constrict and decrease the blood supply to the glomerulus -­‐ Epinephrine and norepinephrine are the neurotransmitters that cause a systemic effect in the vasoconstriction of blood vessel diameter à Increase in blood pressure à Specifically is what causes the afferent arteriole to constrict à Decreases filtration rate -­‐ Blood is still moving through the kidneys in this case, but not as much b) Hormonal: -­‐ Renin angiotensin mechanism à Major mechanism in controlling filtration regulation -­‐ Juxtaglomeruluar cells are modified smooth muscle cells located in the wall of the afferent arteriole that can secrete renin due to low blood pressure o Again: Monitor the pressure of the blood going through afferent arteriole -­‐ Renin (And angiotensin mechanism connection): o Systemically causes vasoconstriction à Increase blood pressure à Decrease filtration rate through constriction of the afferent arteriole in the glomerulus o Renin catalyzes the conversion of angiotensinogen à angiotensin à Causes the adrenal cortex to release aldosterone à Signals the tubules to increase sodium reabsorption that is followed by water due to creation of an osmotic gradient à Ultimately increases blood pressure o *Angiotensin receptors are also located on cells that will cause them to respond to the angiotensin change (More effect will be on the afferent arteriole rather than efferent arteriole side so that it will experience a greater change in diameter) • Overall: Intrinsic and extrinsic mechanism can operate together to achieve the optimal amount of filtration Slide 22: Other factors • Other factors can modify the rates of change caused by the hormonal and extrinsic regulatory mechanisms (Fine tuning function) • Prostaglandins: -­‐ Signaling molecules that can be released by the kidney to function as vasodilators -­‐ Applies when the afferent arteriole has constricted too much due to an intrinsic or extrinsic mechanism à Prostaglandins help open the afferent arteriole up a little bit • Nitric oxide: -­‐ Strong vasodilator -­‐ Can be released due to other stimuli • Adenosine: -­‐ Related to ATP -­‐ Vasodilator throughout most of the body EXCEPT the kidneys where it acts as a vasoconstrictor • Endothelin: -­‐ Chemical secreted by the lining of blood vessels -­‐ Causes vasoconstriction • Review: Urine formation -­‐ Production of urine begins with filtration (Relate to the factors that regulate filtration) -­‐ Once substances are filtered à Fluid from the blood stream is secreted into the tubule à Some substances are reabsorbed and other substances get added to the remaining fluid in the tubule -­‐ AKA: Filtrate forms and modifications occur to the filtrate that all contributes to the process of producing urine Slide 23: Tubular Reabsorption • First step in the modification of filtrate • Tubular reabsorption is an active (Require energy) and passive process (Follow concentration gradients) • Sodium is a very important player in looking at kidney activity + it requires energy to be reabsorbed • 80% of the ATP in the body is used for the reabsorption of sodium in the kidneys • Tubule is made up of epithelial cells with a basement membrane, interstitial space, capillary, and endothelium • For tubular reabsorption, substances pass out of the tubule à Interstitial space à Into the blood vessel • Water movement is a trans-epithelial process: -­‐ Water in the lumen of the tubule has to pass from the lumen into the epithelial cells à Out of the epithelial cells à Across the basement membrane à Interstitial space à Across the endothelium into the capillary • Reabsorption begins immediately in the proximal convoluted tubule (As soon as the filtrate reach the proximal convoluted tubule, substances are taken back up into the blood vessel) • Tight junctions are between epithelial cells that make up the tubule à Water doesn’t leak in between the epithelial cells so it will move across the epithelium • Ions (Solutes): Can take a short cute known as the para-cellular pathway -­‐ Requires energy -­‐ Channel/carrier proteins will generally be along the para-cellular pathway à Used to pump sodium for more efficient movement process that creates an osmotic gradient so that water will follow via trans-epithelial process • Most useful components are almost completely reabsorbed: -­‐ 99% of the water that passes through the kidneys is reabsorbed -­‐ Almost all of the sodium is reabsorbed since the sodium is what creates the osmotic gradient for water to move and follow it -­‐ 100% of glucose is reabsorbed • Waste products such as creatine and uric acid are not reabsorbed OR are secreted into the tubule later for excretion if they were reabsorbed on accident -­‐ Urea is also a waste product à Nitrogen containing compound that comes from the deaminiation of amino acids o Some is reabsorbed to form peptide bonds for protein synthesis but some is urea is secreted back into the tubule to be eliminated Slide 24: Action by Region • Tubular reabsorption (Substances coming out of the tubule) and tubular secretion (Substances secreted into the tubule) both begin immediately in the proximal convoluted tubule à Differences are based on whether or not energy is required • Most of tubular reabsorption occurs in the proximal convoluted tubule (Most active site) -­‐ Only 65% of water is reabsorbed in the proximal convoluted tubule, and -­‐ Other 34% of water is controlled elsewhere in the system o Hormones regulate some of the 34% of water (Discussed later) o Loop of Henle: § The concentration of urine can be regulated because of the ascending and descending limbs by determining how much water moves in this region § A lot of water is reabsorbed if higher concentration of urine is desired § Release a lot of water if dilute urine is desired § Water moves in response to a concentration gradient § Descending limb: Freely permeable to water § Ascending limb: Impermeable to water but is permeable to ions (Sodium being the most important) § The accumulation of ions on the descending side creates the concentration gradient so that water follows and moves out from the descending limb § As filtrate comes through the proximal convoluted tubule and begins to descend down towards the medulla through the descending limb, it is relatively dilute at this point § Filtrate concentrates more as it descends deeper so that more ions and therefore more water are pulled out of the tubule -­‐ *Overall: It’s very important to maintain the concentration gradient that is created by sodium -­‐ Reabsorption finishes up in the distal convoluted tubule and is based on the needs of the body (And not simply based on what we normally need— Occurs in the proximal convoluted tubule and Loop of Henle) o Hormonal dominance in regulation o ADH: § Major hormone in regulating the distal convoluted tubule and collecting duct § Stimulates water reabsorption § The reabsorption of sodium and water can be changed via changing the amount of ADH that is released from the posterior pituitary gland • Kidney failure: -­‐ Loss of concentration gradient so that the kidney is not able to reabsorb substances Slide 25: Urine Production Slide 26: Countercurrent Mechanism • Kidney is efficient in moving materials because it is under a counter current mechanism • The descending limb of the Loop of Henle is in the opposite direction of the ascending limb à As filtrate becomes more concentrated, the concentration gradient that is produced allows water to move (Water moves into a hypertonic environment) • Loop of Henle is surrounded by vasa recta that take up the substances that are reabsorbed from the tubule à Blood flow of the vasa recta ultimately moves in the opposite direction of the tubule as a result • Figure showing the difference between concurrent and countercurrent flow (Focus more on what the figure is showing rather than the explanation): -­‐ One blood vessel is shown moving in 1 direction and the other blood vessel right below it is in the opposite direction -­‐ Flow that arrives at 100% and has an opposite value on the other side at 0% will lead to movement from the high to low concentration -­‐ If the concentration is now at 3% and the other side is still 0%, 3 > 0 so will end up with near 100% transfer instead of 50% transfer that is shown in concurrent flow • Overall: Countercurrent mechanism has to do with blood in the vasa recta vs. filtrate in the tubule Slide 27: Countercurrent Multiplier • Fluids in the proximal convoluted tubule is osmotically equal to the plasma -­‐ In other words: Plasma concentration is equal to the filtrate composition because almost everything is able to pass through the glomerulus except for proteins • Water and ions are reabsorbed in the proximal convoluted tubule where the concentration stays constant until the tubule beings to descend down the Loop of Henle where water is able to move out on the descending limb but solutes are not able to move out -­‐ Filtrate becomes more concentrated as it moves down the descending limb of the Loop of Henle due to an osmotic gradient where the solute are higher outside the tubule than inside the tubule • In the ascending limb of the Loop of Henle, water can NOT move out anymore, but ions are able to -­‐ Filtrate becomes more dilute as ions move out of the ascending limb that is moving back up towards the cortex -­‐ Creates osmotic gradient so that water follows • At the distal convoluted tubule: -­‐ Because so much of the ions and water have been reabsorbed at this point, the filtrate is even more dilute than when it started • In the absence of hormonal stimuli (No ADH present), the distal convoluted tubule and collecting duct are impermeable -­‐ Therefore under these conditions the filtrate at this point will be the same concentration as the urine produced • Vasa recta: -­‐ Water has moved to the interstitial space where it then can move into the vasa recta -­‐ Relates back to the countercurrent mechanism to make sure that useful substances are reabsorbed as much as possible • Collecting ducts: -­‐ Only permeable to urea and NOT water unless ADH is present • Overall formation of urine: Filter the blood à Change the concentration of the filtrate through reabsorption or tubular secretion à Leftover substances in the tubule à Collecting ducts in the renal pyramid à Renal pelvis à Ureter à Urinary bladder à Urethra Slide 28: Renal Gradient • The deeper the tubule distends down into the medulla, the higher the concentration gradient à Why juxtamedullary nephrons give higher concentration gradients than the cortical nephrons • Juxtamedullary nephrons are able to conserve more water the deeper they go into the medulla Slide 29: Countercurrent Exchanger • Vasa recta are freely permeable to water and salt à This protects the medullary concentration gradient Slide 30: Urine Formation • Concentration of urine is going to be under hormonal control of ADH secreted from the posterior pituitary gland • Low levels of ADH cause dilute urine • As ADH production increases, the urine becomes more concentrated • ADH acts primarily on the distal convoluted tubule and the collecting duct to some extent (Both of these are generally NOT permeable to water) • ADH functions in opening channels that exist known as aquaporins -­‐ Allow water to be reabsorbed so that urine becomes more concentrated as it’s passing through the distal convoluted tubule and collecting duct • Suppression of ADH à Closing of the aquaporin channels à Dilute urine • Most water is reabsorbed in the proximal convoluted tubule, and the rest is normally reabsorbed in the Loop of Henle • Aldosterone: -­‐ Affects sodium reabsorption in the Loop of Henle • The regulation of water also regulates blood pressure • Angiotensin Mechanism: Only long-term mechanism for blood pressure regulation through regulation of the amount of fluid in the blood • Individuals with high blood pressure are given diuretics to reduce ADH production à Diluted urine à Lower blood pressure Slide 31: Urinary Bladder • Each kidney has a ureter that collects urine out of the collecting ducts and takes the urine to the urinary bladder • Urinary bladder: Muscular organ that stores fluid • Ureter has an orifice into the bladder • When the supply side of the urinary bladder fills up and gets too full, it stretches so that the ruggae straighten out à Signal sent to the brain that it’s time for urination • When the urinary bladder is relaxed: Ruggae present • 2 urethral sphincters control the urethra: a) Internal sphincter: Smooth muscle that is involuntary b) External sphincter: Skeletal muscle that can be controlled • An involuntary signal to empty the bladder can override by the external sphincter • Trigone: -­‐ Triangle of lines between the 2 orificies and urethral orifice -­‐ Looks like an upside down pyramid • Female urethra: Only carrie urine and is 1.5 inches long • Male urethra: Carries urine and reproductive fluids and is 8 inches long -­‐ Surrounded by prostate glandà Has different segments unlike the female urethra Slide 32 and 34: Micturition • Process of eliminating urine • Urine accumulates in the urinary bladder • Enough urine accumulates to activate the stretch receptors in the wall of the urinary bladder • Signal is sent to the brain • Signal à urethral sphincters so that they are relaxed and open but this can be overridden • Voiding reflex: -­‐ A voluntary act -­‐ Parasympathetic stimulation causes the urinary bladder to contract and external and internal urinary sphincters to relax, but the external one is under voluntary control so that it can close until one is ready to urinate


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