Introduction



IntroductionThe urinary system does more than just get rid of liquid waste. It also:Regulates plasma ion concentrationsRegulates blood volume and blood pressureHelps to stabilize blood pHPrevents the loss of valuable nutrientsEliminates organic matterSynthesizes calcitriol (active form of vitamin D)Prevents dehydrationAids the liver with some of its functionsIntroductionThe urinary system consists of:KidneysAnd the associated nephronsUretersUrinary bladderUrethra The KidneysThe Right KidneyCovered by the liver, hepatic flexure, and duodenumThe Left KidneyCovered by the spleen, stomach, pancreas, splenic flexure, and jejunumThe KidneysThe left kidney is positioned higher than the right kidneyBoth kidneys are capped with the suprarenal glandsThe KidneysThere are three layers of connective tissue that serve to protect the kidneysFibrous capsulePerinephric fatRenal fasciaThe KidneysSuperficial Anatomy of the KidneyA typical kidneySize10 cm long5.5 cm wide3 cm thick150 gSectional viewThe medial indentation is the hilumRenal arteries enter at the hilumRenal veins and ureters exit at the hilumThe KidneysSectional Anatomy of the KidneyConsists of:Renal cortexRenal medulla, which consists of:Several renal lobesRenal pyramidsRenal papillaeRenal columnsRenal pelvis (comprises most of the renal sinus) consists of:Minor calyxMajor calyxThe KidneysThe Blood Supply to the KidneysBeginning with blood in the renal arteries, blood flows to:Segmental arteriesInterlobar arteriesArcuate arteriesCortical radiate arteriesAfferent arteriolesGlomerular capillariesWaste is dropped in the nephronsThe KidneysThe Blood Supply to the Kidneys (continued) After waste is dropped off at the nephrons, blood leaves the kidneys via the following vessels:Glomerular capillariesEfferent arteriolePeritubular capillaries or vasa recta capillariesInterlobular veinsArcuate veinsInterlobar veinsRenal veinInferior vena cavaThe KidneysInnervation of the KidneysUrine production is regulated by autoregulationInvolves reflexive changes in the diameter of nephron arteriolesReceives sympathetic nerve fibers from the celiac and inferior mesenteric gangliaNerve innervation serves to:Regulate renal blood flow and pressureStimulate renin releaseStimulate water and sodium ion reabsorptionThe KidneysStructure and Function of the NephronWaste (glomerular filtrate) material leaves the glomerular capillaries and enters:Glomerular capsuleProximal convoluted tubule (PCT)Nephron loopDistal convoluted tubule (DCT)The KidneysStructure and Function of the NephronThe filtrate that enters the DCT of various nephrons empties into a common tube called the collecting ductThe collecting duct passes through the renal pyramidsFiltrate then enters the: Papillary duct / Minor calyx / Major calyxFiltrate leaves the kidneys:Ureter / Urinary bladder / UrethraThe KidneysStructure and Function of the NephronTwo main types of nephronsCortical nephrons85 percent of the nephrons are corticalMost of the nephron is located in the cortexHave a relatively short nephron loopJuxtamedullary nephrons15 percent of the nephrons are juxtamedullaryCapsule is located near the border of the cortex and the medullaHave a long nephron loopThe KidneysStructure and Function of the NephronMain functions of the nephronReabsorbs useful organic material from the filtrateUrine processingReabsorbs more than 80 percent of the water from the filtratePrevents dehydrationSecretes waste into the filtrate that was missed in an earlier processUrine processingThe KidneysThe Renal Corpuscle Consists of:Glomerular capsuleGlomerular capillaries (glomerulus)Glomerular capsule consists of:Parietal layerMade of squamous cells that are continuous with the lining of the PCTFolds back to form the visceral layerVisceral layerMakes up the epithelial lining of the capillariesThe KidneysThe Renal CorpuscleFiltration within the renal corpuscle involves three layersCapillary endotheliumBasal laminaGlomerular epitheliumThe KidneysThe Renal CorpuscleFiltration within the renal corpuscle Capillary endotheliumThe glomerular capillaries are fenestratedHave openings 0.06–0.1 micronsToo small for blood to pass through (RBC = 7 microns)The KidneysThe Renal CorpuscleFiltration within the renal corpuscle Basal laminaSurrounds the capillary endotheliumThis dense layer restricts the passage of large proteins but permits smaller proteinsPermits the passage of ions and nutrientsThe KidneysThe Renal CorpuscleFiltration within the renal corpuscle Glomerular epitheliumConsists of special cells called podocytesPodocytes have long cellular extensions that wrap around the basal laminaThese extensions have gaps called filtration slitsFiltrate passing through consists of water / ions / small organic molecules (glucose / fatty acids / amino acids / vitamins)Filtrate passing through contains very few plasma proteinsAny potential useful products are reabsorbed in the PCTThe KidneysThe Proximal Convoluted Tubule (PCT)Lined with cuboid epitheliumReabsorbs:All of the organic nutrientsPlasma protein60 percent of the sodium and chloride ions and waterCalcium / Potassium / Magnesium / Bicarbonate / Phosphate / Sulfate ions The KidneysThe Nephron LoopDescending portionWater leaves this portion and enters the bloodstream (thereby preventing dehydration)The capillaries surrounding the nephron loop are called the vasa rectaAscending portionPumps ions (sodium ions and chloride ions) out of the ascending loop thereby preventing the loss of these ionsImpermeable to waterThe KidneysThe Distal Convoluted Tubule (DCT)Active secretion of ions and acidsSelective reabsorption of sodium and calcium ionsVery little reabsorption of waterThe KidneysThe Juxtaglomerular ComplexAlso Called Juxtaglomerular ApparatusLocated in the region of the vascular poleConsists of:Macula densa cellsJuxtaglomerular cellsMesangial cellsProduces two hormonesRenin: involved in regulating blood pressureErythropoietin: involved in erythrocyte productionThe KidneysThe Collecting SystemConsists of:Connecting tubulesCollecting ductsPapillary ductsThe DCTs of several nephrons drain into thecollecting ductThe cells of the collecting ducts make final adjustments to the concentration of the urine that is about to exit the kidneysStructures for Urine Transport, Storage, and EliminationThe UretersExit the kidney at the hilum areaExtend to the urinary bladderEnter the urinary bladder on the posterior/inferior sideThe ureteral openings enter the urinary bladder in the trigone areaStructures for Urine Transport, Storage, and EliminationHistology of the UretersEach ureter consists of three layersInner mucosaMiddle muscular layer (consisting of longitudinal and circular muscles)Adventitia (this is continuous with the fibrous capsule)Structures for Urine Transport, Storage, and EliminationThe Urinary BladderMalesThe base of the urinary bladder is between the rectum and the symphysis pubisFemales The base of the urinary bladder is inferior to the uterus and anterior to the vaginaStructures for Urine Transport, Storage, and EliminationThe Urinary BladderThere are peritoneal folds that assist in maintaining the position of the urinary bladderMedian umbilical ligamentExtends from the anterior/superior border to the umbilical regionLateral umbilical ligamentExtends from the lateral edges to the umbilical regionStructures for Urine Transport, Storage, and EliminationHistology of the Urinary BladderThe muscular layer of the urinary bladder is called the detrusor muscleAt the exit of the urinary bladder and entrance to the urethra is a smooth muscle that makes up the internal urethral sphincterThis is under involuntary controlStructures for Urine Transport, Storage, and EliminationThe UrethraFemale3 to 5 cm in lengthThe external urethral orifice is near the anterior wall of the vaginaMale18 to 20 cm in lengthSubdivided to form the prostatic urethra, membranous urethra, and spongy urethraStructures for Urine Transport, Storage, and EliminationThe UrethraMale (continued)Prostatic urethra Passes through the prostate glandMembranous urethraShort segment that goes through the urogenital diaphragmSpongy urethra (penile urethra) Extends through the penis to the external urethral orificeStructures for Urine Transport, Storage, and EliminationThe UrethraAs the urethra passes through the urogenital diaphragm there is a skeletal muscle that makes up the external urethral sphincterThis is under voluntary control – this is the sphincter we learned to control as an infantWe lose control as we ageWe lose control due to some spinal cord injuriesStructures for Urine Transport, Storage, and EliminationThe Micturition Reflex and UrinationThe first urge to urinate is when the urinary bladder fills to about 200 mlVoluntary effort is needed to relax (and therefore open) the external urethral sphincterWhen the urinary bladder nears capacity, both urethral sphincters will open based on pressureUpon “complete void,” approximately 10 ml of urine still remains ................
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