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Mechanism of urine formation.ppt 22

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Mechanism of urine formation.ppt 22

Mechanism of urine formation.ppt 22

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  • 1. Mechanism of urine formationMechanism of urine formation It means the way by which the urine is formedIt means the way by which the urine is formed.. This occur by three main processThis occur by three main process 11--Glomerular filtrationGlomerular filtration.. 22--tubular reabsorbtiontubular reabsorbtion.. 33--tubular secretiontubular secretion.. Glomerular filtrationGlomerular filtration.. 20%of the blood passed in the glomerular20%of the blood passed in the glomerular capillaries is filtrated into the bowman capsulecapillaries is filtrated into the bowman capsule ,this filtrate is formed of all plasma constituent,this filtrate is formed of all plasma constituent except colloid (plasma protein), this filtrate flowexcept colloid (plasma protein), this filtrate flow into the renal tubule , it can be measure by inulininto the renal tubule , it can be measure by inulin clearance and less accurately by creatininclearance and less accurately by creatinin clearanceclearance
  • 2. The glomerular membraneThe glomerular membrane ItIt is semipermiable membrane.it allow filtration of substance ofis semipermiable membrane.it allow filtration of substance of small molecular weight (nasmall molecular weight (na++,, Glucose, amino acids, creatinin)Glucose, amino acids, creatinin) does not filtrate substance of large molecular weight( proteinsdoes not filtrate substance of large molecular weight( proteins(( It is composed of three layersIt is composed of three layers:: 11--Endothelial layerEndothelial layer.. 22--basement membranebasement membrane.. 33--Layer of epithelial cellsLayer of epithelial cells.. Endothelial cell lining the glomerulus are perforated by thousandsEndothelial cell lining the glomerulus are perforated by thousands of small holes (fenestrateof small holes (fenestrate( .( . Basement membraneBasement membrane It is protein it appear por-less but it contain fenestrate throughIt is protein it appear por-less but it contain fenestrate through which fluids can filtratewhich fluids can filtrate Epithelial cellEpithelial cell.. It is formed of numerous cytoplasmic processIt is formed of numerous cytoplasmic process this cell is called podocytethis cell is called podocyte.. Functionally the glomerular membrane permits the free passagethe glomerular membrane permits the free passage of substance up to 4nm in diameter, does not allow passage ofof substance up to 4nm in diameter, does not allow passage of
  • 3. Factor favoring glomerularFactor favoring glomerular filtrationfiltration 11--The high pressure in the glomerular capillaries (60The high pressure in the glomerular capillaries (60 mmhg) because of the narrow efferent arteriolemmhg) because of the narrow efferent arteriole.. 22--The large surface area in the glomerular capillaryThe large surface area in the glomerular capillary.. 33--The high permeability of the glomerular membraneThe high permeability of the glomerular membrane.. Glomerular capillary blood pressureGlomerular capillary blood pressure:: It is 50 mmhg but part is antagonized by osmoticIt is 50 mmhg but part is antagonized by osmotic pressure of plasma protein 25mmhg , and bypressure of plasma protein 25mmhg , and by intrcapsular pressure 10 mmhg .so the effectiveintrcapsular pressure 10 mmhg .so the effective pressure50-(25+10)= 15 mmhgpressure50-(25+10)= 15 mmhg..
  • 4. Glomerular filtration rateGlomerular filtration rate It is the quantity of glomerular filtrate formed each minute in all nepherons ofIt is the quantity of glomerular filtrate formed each minute in all nepherons of both kidney 125ml/ minutes . The glomerular capillary blood pressure isboth kidney 125ml/ minutes . The glomerular capillary blood pressure is 50mmhg ,in other capillary of the body it is 30 only ,it is 50 not 3050mmhg ,in other capillary of the body it is 30 only ,it is 50 not 30 because:because: renal arteries is wide and short and arises directly from aortarenal arteries is wide and short and arises directly from aorta.. Afferent arteriole is wider than the efferentAfferent arteriole is wider than the efferent.. Factor affecting glomerular filteration rateFactor affecting glomerular filteration rate;; 11--renal blood flowrenal blood flow ; ↑ R BF →↑ G.F.R; ↑ R BF →↑ G.F.R 22--Systemic blood pressureSystemic blood pressure ;↓S.B.P→↓G.F. R. at blood pressure 60;↓S.B.P→↓G.F. R. at blood pressure 60 mmhg→stop G.F.Rmmhg→stop G.F.R.. 33--Constricton of afferent arterioleConstricton of afferent arteriole →↓blood pressure in the glomerulus→↓blood pressure in the glomerulus →↓filtration→↓filtration Dilatation→↑pressure & filtrationDilatation→↑pressure & filtration Mild constrictionMild constriction of efferent arteriole always increase filtration at theof efferent arteriole always increase filtration at the beginningbeginning while strong constrictionwhile strong constriction always increase filtration at thealways increase filtration at the beginning later the osmotic pressure of plasma protein will increase and thisbeginning later the osmotic pressure of plasma protein will increase and this decrease filtrationdecrease filtration.. 44--Sympathetic stimulationSympathetic stimulation constrict both afferent & efferent arteriole soconstrict both afferent & efferent arteriole so decrease blood flow & decrease filtration ( During a state of emergency ).decrease blood flow & decrease filtration ( During a state of emergency ). But sympathetic supply under normal condition has no function on filtrationBut sympathetic supply under normal condition has no function on filtration raterate..
  • 5. 55--Intra capsular pressureIntra capsular pressure It is the pressure influenced on the bowman capsule on theIt is the pressure influenced on the bowman capsule on the glomerular capillariesglomerular capillaries If this pressure ↑→↑G F.RIf this pressure ↑→↑G F.R This pressure increased in case of 1- uretric obstructionThis pressure increased in case of 1- uretric obstruction 22--edema of the kidneyedema of the kidney.. 66--Concentration of plasma proteinConcentration of plasma protein ; ↑Plasma protein; ↑Plasma protein concentration (occur in dehydration )↑Colloidal osmoticconcentration (occur in dehydration )↑Colloidal osmotic pressure →↓G .F.Rpressure →↓G .F.R ↓↓PP con in hypoprotonemia ↓colloidal osmotic pressure →↑G .F RPP con in hypoprotonemia ↓colloidal osmotic pressure →↑G .F R 77--Glomerular capillary permeabilityGlomerular capillary permeability It is increased in case of nephritis ,fever, hypoxia leads toIt is increased in case of nephritis ,fever, hypoxia leads to increased G F Rincreased G F R Filtration fraction (F.F(F.F(( It is the ratio of glomerular filtration rate to renal plasma flowIt is the ratio of glomerular filtration rate to renal plasma flow (0.16-0.2(0.16-0.2(( It is an indication efficiency of filter bedIt is an indication efficiency of filter bed..
  • 6. Function of the renal tubulesFunction of the renal tubules Tubular reabsorptionTubular reabsorption It is the transport of substances from the lumen of the tubules to the blood streamIt is the transport of substances from the lumen of the tubules to the blood stream This process may be active or passiveThis process may be active or passive.. Passive reabsorptionPassive reabsorption This occurs by simple or facilitated diffusion requiring no energy ,down a concentrationThis occurs by simple or facilitated diffusion requiring no energy ,down a concentration gradient ,electrical or osmotic gradientgradient ,electrical or osmotic gradient.. Active reabsorptionActive reabsorption:: This requires energy because it occurs against one or more of the aboveThis requires energy because it occurs against one or more of the above gradients which utilizes enzymatic activity, specific carriers and it is eithergradients which utilizes enzymatic activity, specific carriers and it is either primary or secondary most of glomerular filtration is reabsorped again by theprimary or secondary most of glomerular filtration is reabsorped again by the renal tubules, this reabsorption may need energy active or may not needrenal tubules, this reabsorption may need energy active or may not need energy (passiveenergy (passive(.(. Active reabsorptionActive reabsorption (Primary ,secondary)(Primary ,secondary) eg of activeeg of active reabsorptionreabsorption (na(na++ ,glucose ,amino acids, creatinin ,vitamin,glucose ,amino acids, creatinin ,vitamin uric acids ,vit B12uric acids ,vit B12.(.( Eg , of passive reabsorption as (water, ureaEg , of passive reabsorption as (water, urea(( Load of a substanceLoad of a substance;; The load is the amount of substance which is applied to the renal tubules inThe load is the amount of substance which is applied to the renal tubules in one minutesone minutes Load =plasma level of substance X rate of glomerular filtrationLoad =plasma level of substance X rate of glomerular filtration..
  • 7. ))Tubular or transfer maximum TmTubular or transfer maximum Tm(( Maximum amount of substance in mgs which can be reabsorped or secreted byMaximum amount of substance in mgs which can be reabsorped or secreted by renal tubules in one minuterenal tubules in one minute,, TMTMGG It is the maximum capacity of the renal tubules to reabsorbIt is the maximum capacity of the renal tubules to reabsorb glucose/min=375mg/min in man ,305 mg/min in womanglucose/min=375mg/min in man ,305 mg/min in woman It is the process of glucose reabsorption it is need carrier, the carrier leave theIt is the process of glucose reabsorption it is need carrier, the carrier leave the glucose molecule inside cell and come back to outside to bring anotherglucose molecule inside cell and come back to outside to bring another molecule and so onmolecule and so on.. The amount of glucose reabsorption is limited ,the limitation of the capacity ofThe amount of glucose reabsorption is limited ,the limitation of the capacity of the tubule cell to reabsorb glucose is calledthe tubule cell to reabsorb glucose is called (Tubular maxima for(Tubular maxima for glucose )glucose ) at the blood glucose levelat the blood glucose level 80-180 mg80-180 mg the glucose filtered isthe glucose filtered is completely reabsorped by thecompletely reabsorped by the renal tubules ,when the blood glucoserenal tubules ,when the blood glucose level exceed the threshold valuelevel exceed the threshold value 180mg %180mg % .it start to appear in urine.it start to appear in urine (glucosuria)(glucosuria) because the absorptive power of some tubule becomebecause the absorptive power of some tubule become saturatedsaturated.. With gradual increase in the blood glucose above the threshold value moreWith gradual increase in the blood glucose above the threshold value more renal tubules become saturated until the blood glucose level reach 300mg%renal tubules become saturated until the blood glucose level reach 300mg% all the tubules become saturated, at higher blood glucose level ,no increaseall the tubules become saturated, at higher blood glucose level ,no increase in glucose reabsorption occur, the excess glucose filtered is excreted in thein glucose reabsorption occur, the excess glucose filtered is excreted in the urine as the tubules reach the maximum absorptive capacity it isurine as the tubules reach the maximum absorptive capacity it is 375mg % in males and 305 in females375mg % in males and 305 in females..
  • 8. Phlorizine glucosuriaPhlorizine glucosuria;; It block reabsorption of glucoseIt block reabsorption of glucose.. So this type of glucosureia is called renalSo this type of glucosureia is called renal glucosuria because it is renal in origin but notglucosuria because it is renal in origin but not due to hyperglycemiadue to hyperglycemia.. Alloxan glucosuriaAlloxan glucosuria;; Alloxan destroy beta cells of islands of langerhansAlloxan destroy beta cells of islands of langerhans present in pancreas ,so there is no secretion ofpresent in pancreas ,so there is no secretion of insulin .this leads to hyperglycemia followed byinsulin .this leads to hyperglycemia followed by glucosureiaglucosureia..
  • 9. Glucose transport mechanismGlucose transport mechanism It is transport by a special carrierIt is transport by a special carrier.. It can also transport mannose ,galactose ,xylose.& arbinose ,insulin canIt can also transport mannose ,galactose ,xylose.& arbinose ,insulin can increase rate of facilitated diffusion of glucose up to 20 foldincrease rate of facilitated diffusion of glucose up to 20 fold.. Also amino acids are transported across cell membrane by facilitated diffusionAlso amino acids are transported across cell membrane by facilitated diffusion.. Sodium reabsorptionSodium reabsorption 85%85%of na+ is reabsorped in the proximal convoluted tubules , sodium isof na+ is reabsorped in the proximal convoluted tubules , sodium is carried from the cells into the interstitial place by sodium pump ,The rapidcarried from the cells into the interstitial place by sodium pump ,The rapid diffusion of sodium into the cells is due to ; high sodium permeability. Adiffusion of sodium into the cells is due to ; high sodium permeability. A carrier protein that increase permeability it transport by facilitated diffusioncarrier protein that increase permeability it transport by facilitated diffusion.. It is need energy obtained by ATP breakdownIt is need energy obtained by ATP breakdown.. Na+ take water with it also sodium is positive and take negative ion with it asNa+ take water with it also sodium is positive and take negative ion with it as (Cl & hco3-) ,CL Ion are more absorbed because they are more diffusible(Cl & hco3-) ,CL Ion are more absorbed because they are more diffusible ,so water & CL are reabsorped secondary to na+ Reabsorption so water &,so water & CL are reabsorped secondary to na+ Reabsorption so water & cl are passively reabsorped from proximal convoluted tubule secondary tocl are passively reabsorped from proximal convoluted tubule secondary to active sodium reabsorption ,so it is known as(active sodium reabsorption ,so it is known as( obligatory H2oobligatory H2o reabsorptionreabsorption((.. In distal convoluted tubul, collecting tubules ,H2o reabsorption , in notIn distal convoluted tubul, collecting tubules ,H2o reabsorption , in not secondary to sodium reabsorption .so it may occur or not so itsecondary to sodium reabsorption .so it may occur or not so it is known asis known as facultative water reabsorptionfacultative water reabsorption ,This is,This is under the effect of Antiduretic hormone (ADHunder the effect of Antiduretic hormone (ADH(( When ADH Is high in amount ,the DCT& CT become highly permeable toWhen ADH Is high in amount ,the DCT& CT become highly permeable to
  • 10. Potassium reabsorptionPotassium reabsorption Potassium reabsorption is an active process. 100% ofPotassium reabsorption is an active process. 100% of potassium reabsorbed from the renal tubules ,65% bypotassium reabsorbed from the renal tubules ,65% by the proximal convoluted tubules ,27%by thick portionthe proximal convoluted tubules ,27%by thick portion of the loop of henele,8% by distal tubules & collectingof the loop of henele,8% by distal tubules & collecting ductsducts.. Urea reabsorptionUrea reabsorption Urea is passively reabsorped. As water is reabsorpedUrea is passively reabsorped. As water is reabsorped from the renal tubules.half of the urea filtered isfrom the renal tubules.half of the urea filtered is passively reabsorped ,while the other half passes intopassively reabsorped ,while the other half passes into the urinethe urine.. Creatinin reabsorptionCreatinin reabsorption Not reabsorped & excreted in the urineNot reabsorped & excreted in the urine,, Protein reabsorptionProtein reabsorption It is reabsorped in the proximal convoluted tubules byIt is reabsorped in the proximal convoluted tubules by facilitated diffusionfacilitated diffusion..
  • 11. Tubular secretionTubular secretion;; It means formation of substance in the tubular cell wall,It means formation of substance in the tubular cell wall, and transfer it to the tubular fluids inside tubules asand transfer it to the tubular fluids inside tubules as amonia &amonia & hydrogenhydrogen.. PAHA,Diodrast& CreatininPAHA,Diodrast& Creatinin;; This substances are completely secreted by the renalThis substances are completely secreted by the renal tubules when their plasma level don’t exceed 2mgtubules when their plasma level don’t exceed 2mg %,creatinin are secreted by the proximal tubules%,creatinin are secreted by the proximal tubules.. Potassium ionsPotassium ions Distal tubules& collecting tubules secrete large quantityDistal tubules& collecting tubules secrete large quantity of potassium in the tubular lumen .and it is depend onof potassium in the tubular lumen .and it is depend on na/K ATP ase pump which pump na+ out of the cell atna/K ATP ase pump which pump na+ out of the cell at the same time k+ to inside the cellthe same time k+ to inside the cell.. HydrogenHydrogen:: Proximal tubule ,thick segment of the loop of henel &Proximal tubule ,thick segment of the loop of henel & distal tubule secrete H+ into tubular fluiddistal tubule secrete H+ into tubular fluid..
  • 12. Water excretionWater excretion  NormallyNormally 180 l180 l of fluids are filtered through the glomeruli ,of fluids are filtered through the glomeruli ,urine volume is about 1urine volume is about 1 liter/day,99%liter/day,99% of filtrated water is reabsorbed,of filtrated water is reabsorbed, the rest is treated according tothe rest is treated according to the body needthe body need  The kidney can excrete either watery or concentrated urine.The kidney can excrete either watery or concentrated urine.  Proximal convoluted tubulesProximal convoluted tubules ::  Water is passively reabsorbed as a result of active na+ reabsorption ,this known asWater is passively reabsorbed as a result of active na+ reabsorption ,this known as obligatoryobligatory waterwater reabsorptionnreabsorptionn  Water reabsorption is not affected by ADHWater reabsorption is not affected by ADH  THE osmotic pressure remain isotonicTHE osmotic pressure remain isotonic Descending limb of the loop of henelDescending limb of the loop of henel Permeable to waterPermeable to water.. Impermeable to sodiumImpermeable to sodium.. Ascending limbAscending limb;; Thinner partThinner part Impermeable to waterImpermeable to water Upper thick partUpper thick part Impermeable to waterImpermeable to water Active reabsorption of cl ,passive reabsorption of sodiumActive reabsorption of cl ,passive reabsorption of sodium Distal convoluted tubule ,collecting tubulesDistal convoluted tubule ,collecting tubules Increase ADH, →↑Permeability to H2O & ureaIncrease ADH, →↑Permeability to H2O & urea..
  • 13. Counter current mechanismCounter current mechanism This is a mechanism by which the urine is concentrated in the kidney. It isThis is a mechanism by which the urine is concentrated in the kidney. It is depend on the production & maintenances of the state of hyperosmolalitydepend on the production & maintenances of the state of hyperosmolality or hypertoncity in the renal medullary interstitium by the action & structureor hypertoncity in the renal medullary interstitium by the action & structure which pass in the medulla. The osmolality of the medullary interstitiumwhich pass in the medulla. The osmolality of the medullary interstitium gradually increase from 300 ml osmol in the renal cortex to 1200-1400 mlgradually increase from 300 ml osmol in the renal cortex to 1200-1400 ml osmol / Liter at the renal papillaeosmol / Liter at the renal papillae.. The vasa rectaThe vasa recta Help to keep osmotic gradient in the medulla. Vasa recta is a special bloodHelp to keep osmotic gradient in the medulla. Vasa recta is a special blood supply to loop of henelsupply to loop of henel.. Because any usual blood supply will remove excess na+ in the hypertonicBecause any usual blood supply will remove excess na+ in the hypertonic interstitial fluids' and make it loss of hypertoncityinterstitial fluids' and make it loss of hypertoncity.. But in vasa recta does not occur because vasa recta is formed of 2 limbsBut in vasa recta does not occur because vasa recta is formed of 2 limbs ascending & descending both close to each otherascending & descending both close to each other.. So na+ absorbed from the hypertonic solution cross from ascending toSo na+ absorbed from the hypertonic solution cross from ascending to descending limb also excess H2o reabsorbed from descending limb of thedescending limb also excess H2o reabsorbed from descending limb of the loop of henel & collecting tubules pass to ascending and vasa rectaloop of henel & collecting tubules pass to ascending and vasa recta..
  • 14. So the main function of vasa rectaSo the main function of vasa recta:: Maintain the medullary interstitum hyperosmolality ,this is achieved byMaintain the medullary interstitum hyperosmolality ,this is achieved by operating as counter current exchanger system ( system that can rapidlyoperating as counter current exchanger system ( system that can rapidly exchange of material between its two limb thusexchange of material between its two limb thus;; 11--provide trapping or holding mechanism for nacl & urea in M.Iprovide trapping or holding mechanism for nacl & urea in M.I.. 22--Remove excess water from M.IRemove excess water from M.I.. In descending limbIn descending limb;; The solutes diffuse from M.I into the blood ., While H2o diffuse from blood toThe solutes diffuse from M.I into the blood ., While H2o diffuse from blood to M.I so the blood osmolality riseM.I so the blood osmolality rise.. InIn ascending limbsascending limbs;; The solutes diffuse from the blood into M.I, while H2o diffuse from M.I to theThe solutes diffuse from the blood into M.I, while H2o diffuse from M.I to the blood so the blood osmolality fallsblood so the blood osmolality falls.. In this way, the solutes are trapped in the M.I by continues recirculation whileIn this way, the solutes are trapped in the M.I by continues recirculation while excess water is removed from it and both effects help to maintain of M.Iexcess water is removed from it and both effects help to maintain of M.I hyperosmolalityhyperosmolality NoteNote;; The excess water come from two sourcesThe excess water come from two sources Water that diffuse from descending limb of both V.R & Loop of henelWater that diffuse from descending limb of both V.R & Loop of henel Water that is reabsorbed from the collecting ductsWater that is reabsorbed from the collecting ducts..
  • 15. Increase urea promotes osmosis ofIncrease urea promotes osmosis of water out of the descending thin limbwater out of the descending thin limb of loop of henel,therfore concentrationof loop of henel,therfore concentration of na+cl rise twice normal, so na+clof na+cl rise twice normal, so na+cl diffuse passively out of the thindiffuse passively out of the thin segment into MIsegment into MI
  • 16. The counter current exchangerThe counter current exchanger function of vasa recta is helped byfunction of vasa recta is helped by;; 11--They are highly permeable to both solutes &They are highly permeable to both solutes & H2oH2o.. 22--They constitute the low pressure system ofThey constitute the low pressure system of capillary at which the blood flow is small &capillary at which the blood flow is small & sluggishsluggish.. Such properties allow maximal diffusion ofSuch properties allow maximal diffusion of solutes from ascending limb of V .R into M.Isolutes from ascending limb of V .R into M.I and the water in the opposite direction andand the water in the opposite direction and minimize the loss of solutes into the bloodminimize the loss of solutes into the blood leaving the renal medullaleaving the renal medulla..
  • 17. The vasa rectaThe vasa recta Help to keep osmotic gradient in the medullaHelp to keep osmotic gradient in the medulla.. Vasa rectaVasa recta is a special blood supplyis a special blood supply to the loop of henelto the loop of henel.. Because any usual bllod supply will removeBecause any usual bllod supply will remove excess sodium in the hypertonic solution andexcess sodium in the hypertonic solution and make it loss to hypertonicitymake it loss to hypertonicity.. But in vasa recta does not occur because vasaBut in vasa recta does not occur because vasa recta is formed of two limb ascending andrecta is formed of two limb ascending and dscending both close to each otherdscending both close to each other.. So sodium absorbed from the hypertonicSo sodium absorbed from the hypertonic solution cross from ascending to dscending limbsolution cross from ascending to dscending limb.. Also excess water reabsorbed from descendingAlso excess water reabsorbed from descending limb of loop of henel , collecting tubules pass tolimb of loop of henel , collecting tubules pass to ascending vasa rectaascending vasa recta..