Y khoa, y dược - The urinary system: Part A

25 The Urinary System: Part AUrinary System OrgansKidneys are major excretory organsUrinary bladder is the temporary storage reservoir for urineUreters transport urine from the kidneys to the bladderUrethra transports urine out of the bodyFigure 25.1Esophagus (cut)Inferior vena cavaAdrenal glandHepatic veins (cut)Renal arteryRenal hilumRenal veinIliac crestKidneyUreterUrinarybladderUrethraAortaRectum (cut)Uterus (part of female reproductive system)Kidney FunctionsIt removes from blood toxins, metabolic wastes, and excess ions It regulates blood volume, blood pressure, blood chemistry and blood pHKidney FunctionsGluconeogenesis during prolonged fastingEndocrine functions Renin: regulation of blood pressure and kidney function Erythropoietin: regulation of RBC productionActivation of vitamin D Kidney AnatomyRetroperitoneal, in the superior lumbar regionRight kidney is lower than the left Convex lateral surface, concave medial surface Renal hilum leads to the renal sinusUreters, renal blood vessels, lymphatics, and nerves enter and exit at the hilumFigure 25.2aBody wall• Perirenal fat capsuleRenalarteryRenalveinInferior vena cavaAorta• Fibrous capsule• Renal fascia anterior posteriorSupportivetissue layersBody ofvertebra L2PeritoneumPeritoneal cavity(organs removed)AnteriorPosterior(a)Kidney AnatomyLayers of supportive tissueRenal fascia The anchoring outer layer of dense fibrous connective tissue Perirenal fat capsule A fatty cushion Fibrous capsulePrevents spread of infection to kidneyInternal AnatomyRenal cortexA granular superficial regionRenal medullaThe cone-shaped medullary (renal) pyramids separated by renal columnsLobe (Pyramid)A medullary pyramid and its surrounding cortical tissueInternal AnatomyPapilla Tip of pyramid; releases urine into minor calyxMinor calyx Collects urine from papillaMajor calyxThe branching channels of the renal pelvis thatCollect urine from minor calyces Empty urine into the pelvisInternal AnatomyRenal pelvis The funnel-shaped tube within the renal sinu Urine flows from the pelvis to ureters Figure 25.3Renal cortexRenal medullaMajor calyxPapilla ofpyramidRenal pelvisUreterMinor calyxRenal columnRenal pyramid in renal medullaFibrous capsuleRenalhilum(a) Photograph of right kidney, frontal section(b) Diagrammatic viewFigure 25.4aCortical radiate vein Cortical radiate arteryArcuate veinArcuate arteryInterlobar veinInterlobar arterySegmental arteriesRenal arteryRenal veinRenal pelvisUreterRenal medullaRenal cortex(a) Frontal section illustrating major blood vesselsFigure 25.4bAorta Renal artery Segmental artery Interlobar artery Arcuate artery Cortical radiate artery Afferent arteriole Glomerulus (capillaries)Nephron-associated blood vessels(see Figure 25.7)Inferior vena cava Renal veinInterlobar veinArcuate veinCortical radiatevein Peritubularcapillariesand vasa rectaEfferent arteriole (b) Path of blood flow through renal blood vesselsNephronsStructural and functional units that form urine~1 million per kidneyTwo main partsGlomerulus: a tuft of capillaries Renal tubule: begins as cup-shaped glomerular (Bowman’s) capsule surrounding the glomerulusFigure 25.5NephronsRenal corpuscleGlomerulus + its glomerular capsuleFenestrated glomerular endotheliumAllows filtrate to pass from plasma into the glomerular capsuleRenal TubuleRenal tubule consists of:Glomerular capsuleProximal convoluted tubuleLoop of HenleDistal convoluted tubuleRenal TubuleGlomerular capsuleParietal layer: simple squamous epitheliumVisceral layer: branching epithelial podocytesExtensions terminate in foot processes that cling to basement membraneFiltration slits allow filtrate to pass into the capsular spaceFigure 25.5Glomerular capsule: parietal layerFigure 25.5Fenestratedendotheliumof the glomerulusPodocyte BasementmembraneGlomerular capsule: visceral layerRenal TubuleProximal convoluted tubule (PCT) Cuboidal cells with dense microvilli and large mitochondriaFunctions in reabsorption and secretionConfined to the cortexFigure 25.5MicrovilliMitochondriaHighly infolded plasma membraneProximal convoluted tubule cellsRenal TubuleLoop of Henle with descending and ascending limbs Thin segment usually in descending limbSimple squamous epitheliumFreely permeable to waterThick segment of ascending limbCuboidal to columnar cellsFigure 25.5Loop of Henle (thin-segment) cellsRenal TubuleDistal convoluted tubule (DCT)Cuboidal cells with very few microvilli Function more in secretion than reabsorptionConfined to the cortexFigure 25.5Distal convoluted tubule cellsCollecting DuctsReceive filtrate from many nephronsFuse together to deliver urine through papillae into minor calycesCollecting DuctsCell typesIntercalated cellsCuboidal cells with microvilli Function in maintaining the acid-base balance of the bodyFigure 25.5Intercalated cellPrincipal cellCollecting duct cellsCollecting DuctsPrincipal cellsCuboidal cells without microvilliHelp maintain the body’s water and salt balanceFigure 25.5Fenestratedendotheliumof the glomerulusMicrovilliCortexMedullaPodocyte BasementmembraneMitochondriaHighly infolded plasmamembrane ProximalconvolutedtubuleDistalconvolutedtubule• Descending limbLoop of Henle• Ascending limb• Glomerular capsuleRenal corpuscle• GlomerulusThick segmentCollectingduct Intercalated cellPrincipal cellThin segmentProximal convoluted tubule cellsGlomerular capsule: parietal layerGlomerular capsule: visceral layerDistal convoluted tubule cellsLoop of Henle (thin-segment) cellsCollecting duct cellsRenal cortexRenal medullaRenal pelvisUreterKidneyNephronsCortical nephrons—85% of nephrons; almost entirely in the cortexJuxtamedullary nephronsLong loops of Henle deeply invade the medulla Extensive thin segmentsImportant in the production of concentrated urineFigure 25.7aCortical nephron• Has short loop of Henle and glomerulus further from the corticomedullary junction• Efferent arteriole supplies peritubular capillariesJuxtamedullary nephron• Has long loop of Henle and glomerulus closer to the corticomedullary junction• Efferent arteriole supplies vasa rectaCorticomedullaryjunctionUreterRenal pelvisKidneyCortexMedulla(a)Cortical radiate veinCortical radiate arteryAfferent arterioleAfferent arterioleCollecting ductDistal convoluted tubuleEfferent arterioleVasa rectaLoop of HenleArcuate arteryArcuate veinPeritubular capillariesGlomerular capillaries (glomerulus)Glomerular(Bowman’s) capsuleRenalcorpuscleAscending or thick limb of the loop of HenleDescendingor thin limb of loop of HenleEfferent arteriole Proximalconvoluted tubuleNephron Capillary BedsGlomerulus Afferent arteriole  glomerulus  efferent arterioleSpecialized for filtrationBlood pressure is high becauseAfferent arterioles are smaller in diameter than efferent arteriolesArterioles are high-resistance vesselsNephron Capillary BedsPeritubular capillariesLow-pressure, porous capillaries adapted for absorption Arise from efferent arteriolesCling to adjacent renal tubules in cortexEmpty into venulesNephron Capillary BedsVasa rectaLong vessels parallel to long loops of HenleArise from efferent arterioles of juxtamedullary nephrons Function in formation of concentrated urineFigure 25.7aCortical nephron• Has short loop of Henle and glomerulus further from the corticomedullary junction• Efferent arteriole supplies peritubular capillariesJuxtamedullary nephron• Has long loop of Henle and glomerulus closer to the corticomedullary junction• Efferent arteriole supplies vasa rectaCorticomedullaryjunctionUreterRenal pelvisKidneyCortexMedulla(a)Cortical radiate veinCortical radiate arteryAfferent arterioleAfferent arterioleCollecting ductDistal convoluted tubuleEfferent arterioleVasa rectaLoop of HenleArcuate arteryArcuate veinPeritubular capillariesGlomerular capillaries (glomerulus)Glomerular(Bowman’s) capsuleRenalcorpuscleAscending or thick limb of the loop of HenleDescendingor thin limb of loop of HenleEfferent arteriole Proximalconvoluted tubuleVascular Resistance in MicrocirculationHigh resistance in afferent and efferent arteriolesCauses blood pressure to decline from ~95 mm Hg to ~8 mm Hg in kidneysVascular Resistance in MicrocirculationResistance in afferent arteriolesProtects glomeruli from fluctuations in systemic blood pressureResistance in efferent arteriolesReinforces high glomerular pressureReduces hydrostatic pressure in peritubular capillaries Juxtaglomerular Apparatus (JGA)One per nephronImportant in regulation of filtrate formation and blood pressureInvolves modified portions of theDistal portion of the ascending limb of the loop of HenleAfferent (sometimes efferent) arteriole Juxtaglomerular Apparatus (JGA)Granular cells (juxtaglomerular, or JG cells)Enlarged, smooth muscle cells of arterioleSecretory granules contain reninAct as mechanoreceptors that sense blood pressureJuxtaglomerular Apparatus (JGA)Macula densaTall, closely packed cells of the ascending limbAct as chemoreceptors that sense NaCl content of filtrate Figure 25.8GlomerulusGlomerular capsuleAfferent arterioleEfferent arterioleRed blood cellPodocyte cell body (visceral layer)Foot processesof podocytesParietal layerof glomerularcapsuleProximaltubule cellLumens of glomerularcapillariesEndothelial cellof glomerularcapillaryEfferent arteriole• Macula densa cells of the ascending limb of loop of Henle• Granular cells• Extraglomerular mesangial cellsAfferent arterioleCapsularspaceRenal corpuscleJuxtaglomerularapparatusMesangial cellsbetween capillariesJuxtaglomerularapparatusFiltration MembranePorous membrane between the blood and the capsular spaceConsists ofFenestrated endothelium of the glomerular capillariesVisceral membrane of the glomerular capsule (podocytes with foot processes and filtration slits)Gel-like basement membrane (fused basal laminae of the two other layers)Figure 25.9aGlomerular capillarycovered by podocyte-containing visceral layer of glomerular capsuleGlomerular capillaryendothelium (podocyte covering and basement membrane removed)Proximal convolutedtubuleParietal layerof glomerular capsuleAfferentarterioleGlomerular capsular spaceFenestrations(pores)EfferentarteriolePodocytecell bodyFoot processesof podocyteFiltration slitsCytoplasmic extensionsof podocytes(a) Glomerular capillaries and the visceral layer of the glomerular capsuleFiltration MembraneAllows passage of water and solutes smaller than most plasma proteinsFenestrations prevent filtration of blood cellsNegatively charged basement membrane repels large anions such as plasma proteinsSlit diaphragms also help to repel macromoleculesFiltration MembraneGlomerular mesangial cellsEngulf and degrade macromoleculesCan contract to change the total surface area available for filtrationFigure 25.9c(c) Three parts of the filtration membraneFenestration(pore)Filtrate incapsularspaceFoot processesof podocyteFiltration slitSlit diaphragmCapillaryFiltration membrane• Capillary endothelium• Basement membrane• Foot processes of podocyte of glomerular capsulePlasmaKidney Physiology: Mechanisms of Urine FormationThe kidneys filter the body’s entire plasma volume 60 times each dayFiltrateBlood plasma minus proteinsUrine5 nm are not filtered (e.g., plasma proteins) and function to maintain colloid osmotic pressure of the bloodNet Filtration Pressure (NFP)The cumulative pressure responsible for filtrate formation (10 mm Hg)Net Filtration Pressure (NFP)Determined byGlomerular hydrostatic pressure (HPg) the chief force Two opposing forces:Colloid osmotic pressure of glomerular blood (OPg) Capsular hydrostatic pressure (HPc)NFP = HPg – (OPg + HPc)Figure 25.11GlomerularcapsuleAfferentarteriole10 mm HgNetfiltrationpressureGlomerular (blood) hydrostatic pressure(HPg = 55 mm Hg)Blood colloid osmotic pressure(Opg = 30 mm Hg)Capsular hydrostatic pressure(HPc = 15 mm Hg)Glomerular Filtration Rate (GFR)Volume of filtrate formed by the kidneys (120–125 ml/minute)Governed by (and directly proportional to)Total surface area available for filtrationFiltration membrane permeabilityNFPRegulation of Glomerular FiltrationGFR is tightly controlled by two types of mechanismsIntrinsic controls (renal autoregulation)Act locally within the kidneyExtrinsic controlsNervous and endocrine mechanisms that maintain blood pressure, but affect kidney functionIntrinsic ControlsMaintains a nearly constant GFR when MAP is in the range of 80–180 mm HgTwo types of renal autoregulationMyogenic mechanism (Chapter 19)Tubuloglomerular feedback mechanism, which senses changes in the juxtaglomerular apparatusIntrinsic Controls: Myogenic Mechanism BP  constriction of afferent arteriolesHelps maintain normal GFRProtects glomeruli from damaging high BP BP  dilation of afferent arteriolesHelps maintain normal GFRIntrinsic Controls: Tubuloglomerular Feedback MechanismFlow-dependent mechanism directed by the macula densa cellsIf GFR increases, filtrate flow rate increases in the tubuleFiltrate NaCl concentration will be high because of insufficient time for reabsorptionIntrinsic Controls: Tubuloglomerular Feedback MechanismMacula densa cells of the JGA respond to NaCl by releasing a vasoconstricting chemical that acts on the afferent arteriole   GFRThe opposite occurs if GFR decreases.Extrinsic Controls: Sympathetic Nervous SystemUnder normal conditions at restRenal blood vessels are dilatedRenal autoregulation mechanisms prevailExtrinsic Controls: Sympathetic Nervous SystemUnder extreme stressNorepinephrine is released by the sympathetic nervous systemEpinephrine is released by the adrenal medulla Both cause constriction of afferent arterioles, inhibiting filtration and triggering the release of renin Extrinsic Controls: Renin-Angiotensin MechanismTriggered when the granular cells of the JGA release reninangiotensinogen (a plasma globulin) resin  angiotensin Iangiotensin converting enzyme (ACE)  angiotensin IIEffects of Angiotensin IIConstricts arteriolar smooth muscle, causing MAP to rise Stimulates the reabsorption of Na+Acts directly on the renal tubulesTriggers adrenal cortex to release aldosterone Stimulates the hypothalamus to release ADH and activates the thirst centerEffects of Angiotensin IIConstricts efferent arterioles, decreasing peritubular capillary hydrostatic pressure and increasing fluid reabsorptionCauses glomerular mesangial cells to contract, decreasing the surface area available for filtrationExtrinsic Controls: Renin-Angiotensin MechanismTriggers for renin release by granular cellsReduced stretch of granular cells (MAP below 80 mm Hg)Stimulation of the granular cells by activated macula densa cellsDirect stimulation of granular cells via 1-adrenergic receptors by renal nervesFigure 25.12Stretch of smoothmuscle in walls of afferent arteriolesBlood pressure inafferent arterioles; GFRVasodilation ofafferent arteriolesGFRMyogenic mechanismof autoregulationRelease of vasoactive chemical inhibitedIntrinsic mechanisms directly regulate GFR despitemoderate changes in blood pressure (between 80 and 180 mm Hg mean arterial pressure).Extrinsic mechanisms indirectly regulate GFRby maintaining systemic blood pressure, whichdrives filtration in the kidneys.Tubuloglomerularmechanism ofautoregulationHormonal (renin-angiotensin)mechanismNeural controlsSYSTEMIC BLOOD PRESSUREGFRMacula densa cellsof JG apparatus of kidneyFiltrate flow andNaCl in ascendinglimb of Henle’s loopTargetsGranular cells ofjuxtaglomerularapparatus of kidneyAngiotensinogenAngiotensin IIAdrenal cortexSystemic arterioles(+)ReninReleaseCatalyzes cascaderesulting in conversion(+)(+)(+)Kidney tubulesAldosteroneReleasesTargetsVasoconstriction;peripheral resistanceBlood volume Na+ reabsorption;water followsSystemicblood pressure(+)(+) (–)IncreaseDecreaseStimulatesInhibitsBaroreceptors inblood vessels ofsystemic circulationSympatheticnervous system(+)(–)Vasodilation ofafferent arterioles