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Mizzou MPP 3202 - Chapter 19

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Chapter 19: The KidneysRenal StructureSlide 3Slide 4Slide 5Functions of the KidneysRenal FunctionNephron: Functional UnitFiltration, Reabsorption, SecretionGlomerulusPowerPoint PresentationGlomerular Filtration Rate (GFR)Slide 13GFR RegulationTubuloglomerular FeedbackSlide 16ReabsorptionReabsorption: Na+ CotransportSecretionExcretionClearanceSlide 22Chapter 19: The Kidneys•Anatomy•Kidney function•Filtration•Reabsorption•Secretion•ExcretionRenal StructureGross examination of the kidney reveals three clearly demarcated anatomical areas.Cortex constitutes the major portion of the kidney and receives a disproportionately higher percentage (90%) of the blood flow.Medulla (6-10%).Papilla (1-2%).Renal StructureRenal StructureCortexMedullaRenal Structure•The kidneys receive 22% of cardiac output (1.1 L/min); unlike other organs, renal blood flow far exceeds metabolic demand.•Flexibility.•All blood flow is filtered through glomeruli; as such mechanisms that regulate RBF are closely linked to control of GFR. •Renal Blood Flow = 1100 ml/min•Renal Plasma Flow = 605 ml/min (hematocrit = 45%)•Glomerular Filtration Rate = 125 ml/min•Filtration Fraction = GFR/RPF (125/605) = 21%•The high GFR allows for precise control of fluid volume/composition and rapid removal of waste.Two capillary bedsFunctions of the Kidneys•Regulation of extracellular fluid volume and blood pressure- important role•Regulation of osmolarity•Maintenance of ion balance•Homeostatic regulation of pH•Excretion of waste•Production of hormonesRenal FunctionFormation of urine involves three basic processes:1) ultrafiltration of plasma by the glomerulus2) reabsorption of water and solutes from the ultrafiltrate3) secretion of selected solutes into the tubular fluid (active, requires energy).From Textbook of Medical PhysiologyNephron: Functional UnitGlomerulusCapillary bed; filtrationProximal TubuleReabsorption (60%)SecretionSodium and water similarImportant for making concentration urineLoop of HenleAscending Limb is water impermeableDistal TubuleCollecting DuctWater permeable in presence of ADH (vasopressin)Filtration, Reabsorption, SecretionGlomerulusThe epithelium around glomerular capillariesis modified into podocytes.EfferentarterioleBowman’scapsuleCapsularepitheliumThickascendinglimb ofloop ofHenleAfferentarterioleLumen ofBowman’scapsuleGlomerularcapillaryProximaltubulePodocyteThe glomerular capillary endothelium, basal lamina,and Bowman’s capsule epithelium create a three-layer filtration barrier. Filtered substances passthrough endothelial pores and filtration slits.Foot processof podocyteFiltration slitBasal laminaPores inendotheliumCapillarylumenFilteredmaterialLumen ofBowman’scapsuleGlomerulusGlomerular Filtration Rate (GFR)•Influenced by two factors1. Net filtration pressure–Hydrostatic pressure – colloid osmotic pressure – fluid pressure out of capillaries2. Filtration coefficient–High surface area of glomerular capillaries available for filtration–High permeability of interface between the capillary and Bowman’s capsuleGlomerular Filtration Rate (GFR)GFR Regulation•Myogenic response–Intrinsic ability of vascular smooth muscle to respond to pressure changes–Similar to autoregulation in other systemic arterioles•Tubuloglomerular feedback–Paracrine control•Hormones and autonomic neurons–By changing resistance in arterioles–By altering the filtration coefficientTubuloglomerular FeedbackThe nephron loops back on itself so that theascending limb of the loop of Henle passesbetween the afferent and efferent arterioles.The macula densa cells sense distaltubule flow and release paracrines thataffect afferent arteriole diameter.Efferent arterioleBowman’scapsuleGlomerulusProximaltubuleMaculadensacellsAscendinglimb of loopof HenleAfferentarterioleEndotheliumGranular cells secrete renin, an enzymeinvolved in salt and water balance.Tubuloglomerular FeedbackTubuloglomerular feedback helps GFR autoregulation.GFR increases.Flow through tubule increases.Flow past macula densa increases.Paracrine from maculadensa to afferent arterioleAfferent arteriole constricts.Resistance in afferentarteriole increases.Hydrostatic pressurein glomerulus decreases.GFR decreases.LoopofHenleAfferent arterioleGranular cellsMacula densaBowman’s capsuleCollectingductProximaltubuleEfferent arterioleGlomerulusDistal tubuleReabsorption•Epithelial transport (transcellular transport)–Substances cross apical and basolateral membranes of the tubule epithelial cells•Paracellular pathway–Substances pass through the cell–cell junction between two adjacent cells•Low hydrostatic pressure in peritubular capillariesFiltrate issimilar tointerstitialfluid.Na+AnionsH2OK+, Ca2+,ureaTubule lumenTubularepitheliumExtracellular fluidPermeable solutes are reabsorbedby diffusion through membranetransporters or by the paracellularpathway.Water moves by osmosis, followingsolute reabsorption. Concentrationsof other solutes increase as fluidvolume in lumen decreases.Electrochemical gradient drivesanion reabsorption.Na+ is reabsorbed by activetransport.Reabsorption: Na+ CotransportThis figure shows glucose, but amino acids, other organic metabolites,and some ions such as phosphate are also absorbed by Na+-dependentcotransport.[Na+] high[glu] low[Na+] low[glu] highSGLTgluNa+Na+gluGLUTApicalmembraneBasolateralmembraneATP[glu] low[Na+] highK+Glucose and Na+reabsorbedNa+ moving down its electro-chemical gradient uses theSGLT protein to pull glucoseinto the cell against itsconcentration gradient.Glucose diffuses out thebasolateral side of the cellusing the GLUT protein.Na+ is pumped out byNa+-K+-ATPase.Secretion•Transfer of molecules from extracellular fluid into lumen of the nephron –Active process•Important in homeostatic regulation–K and H•Increasing secretion enhances nephron excretion•A competitive process–Penicillin and probenecidProximal tubule secretion of organic anions by the organic anion transporter (OAT) is an example of tertiary active transport.FiltrateTubule lumenProximal tubule cellInterstitial fluid[Na+] lowNa+Na+Na+K+ATPNaDCOATKG–NaDC?MetabolismKG–concentratesKG–KG–OA–OA–OA–A–ApicalmembraneBasolateralmembraneOrganic anionsenter the lumenby facilitateddiffusion.Direct active transport.The Na+-K+-ATPase keepsintracellular [Na+] low.Secondary indirect active transport.The Na+-dicarboxylate cotransporter(NaDC)


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Mizzou MPP 3202 - Chapter 19

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