Excretory System - structure function

Part 1 – Anatomy & PhysiologyMammalian Excretory System

Excretionremoval of metabolic wastedoes not include fecesfeces is what your body did not use, therefore notmetabolic waste

Vertebrate Excretory SystemHandles osmoregulation:Dispose metabolic wasteControl body fluid compositionaverage person loses 2L of liquids a daysuggested to consume 2L H2O / dayInvolves kidneys

Roles of Kidneyblood filtrationwaste excretionacid / base balanceblood pressure regulationhormone secretion

Mammalian KidneyA pairBean-shaped10 cm longBuilt of tubules and ductsthat carry urineContains a densenetwork of capillaries

Mammalian Kidney

Urine ExcretionKidneysUreter (duct)Urinary bladderUrethra (duct)Fig. 44.21

Urinesolution of metabolic wastewatersaltsorganic compoundsurea and uric acidother wastes / toxinsfluid for urine comes from filtered blood andextracellular fluid (ECF)

Urine ExcretionWhen ~200 mL of urine has collected in thebladder, the walls stretch and signals are sentto the brain.At ~600 mL, urine will involuntarily bereleased.

Urinary Tract Infection (UTI)Caused by bacterial growth in the urethra orbladderSymptoms:frequent urinationsensation of needing to urinate (even is there islittle to pass)blood in urinedischarge in urine (cloudiness)

Kidney Stonescrystallization of someurine solutesa 2 – 3 mm stone canobstruct flow to theureterTreatment:increased waterconsumptionsurgery

Internal Kidney Anatomyhttp://www.gisbornesc.vic.edu.au/home/jans/home/kidney.htmRenalmedullaRenalcortex

Kidney Structurerenal cortex: outside ofkidneyrenal medulla: middleof kidneyrenal pelvis: innerportion of kidney

Nephron AnatomyNephron: functional unitAbout a million nephrons make up thekidney.Fig. 44.21

Nephron AnatomyConsists of tubules/ductssurrounded by bloodvessels.Fig. 44.21

Activity1. Look at blood flowthrough the nephron(red & blue). Translateit into a flow chart.2. Look at the flow offiltrate through thetubules (yellow) of thenephron. Translate itinto a flow chart.

Blood Flow in KidneyBlood supply: renal arteryand veinBlood enters kidney throughrenal arteryrenal arteries stem from theaortaFiltered blood exits kidneythrough renal veinrenal veins flow into theinferior vena cavahttp://www.taguig.com/newitem/kidney.jpg

Blood Flow in NephronRenal arteryAfferent arterioleCapillaries of glomerulusEfferent arteriolePeritubular capillariesVasa rectaRenal vein

Blood Vessels in the NephronVessels LocationAfferentarterioleFrom renal artery to glomerulus.Capillaries ofthe glomerulusCapillaries in the Bowman’s capsule.EfferentarterioleCapillaries converge. Exitglomerulus.PeritubularcapillariesSurrounds proximal and distaltubules.Vasa recta Surrounds loop of Henle.Countercurrent. To renal vein.

Excretory SystemOverviewFiltration of bloodReabsorption ofvaluable substancesSecretion of toxins andexcess ionsExcretion of thecontents of tubuleFig. 44.17

FiltrationFiltering bloodBlood pressure forces fluidthrough filterTransport epithelium acts asfilterMovement of substances:Capillaries of glomerulus lumen of Bowman’s capsuleFiltrate = portion that isinside tubules

ReabsorptionMovement of substances:filtrate  interstitial fluid bloodThus reabsorbed back into the bodyProtein transporters movenutrients into interstitial fluid andbloodReabsorption saves us fromhaving to continuously replenishour body with fluidUrine is 4x more concentratedthan blood

SecretionMovement of substances:blood interstitial fluid  filtrateThus materials will eventually beexcreted from bodyOpposite of reabsorptionProtein transporters move wastesfrom blood to interstitial fluid tonephronSubstances removed:Nonessential or excess solutesWastetoxins

ExcretionExit of filtrate out ofbodyFiltrate is now calledurine

Pathway of Filtrate in kidneyBowman’s capsuleProximal tubuleLoop of HenleDistal tubuleCollecting ductFig. 44.21

Filtrate & Blood flowPathway of filtrate Function Blood vesselBowman’s capsule Filtration Capillaries ofglomerulusProximal tubule Reabsorption& secretionPeritubularcapillariesLoop of Henle Reabsorption Vasa RectaDistal tubule Reabsorption& secretionPeritubularcapillariesCollecting Duct Reabsorption& excretion

1. Bowman’sCapsule Activetransport Passivetransport

1. Bowman’s CapsuleGlomerulus: ball ofcapillariesBowman’s capsule: blindend of tubule thatsurrounds glomerulusNutrients flow fromglomerulus intoBowman’s capsule dueto high blood pressureflow (65 mm Hg; normal~ 25 mm Hg)Fig. 44.21

Glomerulus & Bowman’s Capsule

1. Bowman’s CapsuleRetain large molecules (cells,protein etc.)Filter is non-selective for smallmoleculesContains waterContains small solutes: salt, sugar,amino acid, nitrogenous wastewater and dissolved solutes leaveglomerulus; enter Bowman’scapsulewaterNa+H+Cl-glucoseamino acidsvitaminsmineralsureauric acid

FiltrationSolute Bowman’sCapsulewater YesNaCl YesH+YesHCO3- Yesglucose Yesamino acids Yesvitamins / minerals Yesurea / uric acid Yesplasma proteins Nored blood cells Noplatelets No

2. ProximalTubule

2. Proximal TubuleSelective reabsorption of nutrientsinto capillaries (peritubular)Active transport (need transporters) ofvaluable nutrients (glucose, amino acids,vitamins) and salt (NaCl)Passive transport of water by osmosispH determined by:HCO3- reabsorptionH+ and NH3 secretionSecretion of drugs and other poisonsHCO3-, K+Na+, Cl-H2Oamino acidsglucosevitaminsH+, NH3

Nutrient FlowSolute ProximaltubuleLoop ofHenleDistaltubuleCollectingductwaterNaClH+HCO3-glucoseamino acidsvitamins / mineralsurea / uric acid

Nutrient FlowSolute ProximaltubuleLoop ofHenleDistaltubuleCollectingductwater RNaCl RH+SHCO3- Rglucose Ramino acids Rvitamins / minerals Rurea / uric acid S

3. Loop of Henle:Descending limb

H2O3. Loop of Henle:Descending LimbTransport epithelium is only permeable towaterImpermeable to salt and other small solutesReabsorption of water by osmosisInterstitial fluid is hyperosmoticOsmolarity of interstitial fluid becomesprogressively greater from outer cortex to innermedullaFiltrate becomes more concentrated as itmoves down into the medulla

Things to keep in mindWhat is the mechanism that maintains theosmolarity difference in the nephron?What keeps the osmolarity of the interstitialfluid to become progressively greater fromthe outer cortex to the inner medulla?

4. Loop of Henle:Ascending limb

NaCl4. Loop of Henle:Ascending LimbTransport epithelium is permeable tosalt but not waterThin segment: NaCl passive transport Diffusion possible due to concentratedfiltrate Increases osmolarity of the inner medullaThick segment: NaCl active transportFiltrate becomes more dilute as itmoves up towards the cortex

Nutrient FlowSolute ProximaltubuleLoop ofHenleDistaltubuleCollectingductwater RNaCl RH+SHCO3- Rglucose Ramino acids Rvitamins / minerals Rurea / uric acid S

Nutrient FlowSolute ProximaltubuleLoop ofHenleDistaltubuleCollectingductwater R R (desc)NaCl R R (ascn)H+SHCO3- Rglucose Ramino acids Rvitamins / minerals Rurea / uric acid S

Urine ConcentrationFig. 44.23

CountercurrentFlow Flow of filtrate in theloop of Henle and flowof blood in the vasarecta are in oppositedirections Allows the lessconcentrate filtrate tobe next to the lessconcentrated blood(and vice versa) Contributes toestablishing theosmotic gradient Increase the efficiencyof reabsorptionhttp://www.austincc.edu/apreview/NursingPics/RenalPics/Picture25.jpg

5. DistalTubule

5. Distal tubuleRegulates K+ and NaCl concentrations bycontrolling active transport of:K+ secretionNaCl reabsorptionContributes to pH regulationsecretion of H+reabsorption of bicarbonate (HCO3-)

Nutrient FlowSolute ProximaltubuleLoop ofHenleDistaltubuleCollectingductwater R R (desc)NaCl R R (ascn)H+SHCO3- Rglucose Ramino acids Rvitamins / minerals Rurea / uric acid S

Nutrient FlowSolute ProximaltubuleLoop ofHenleDistaltubuleCollectingductwater R R (desc) RNaCl R R (ascn) RH+S SHCO3- R Rglucose R Ramino acids R Rvitamins / minerals R Rurea / uric acid S S

6. CollectingDuct

6. Collecting DuctCollects from several nephronsCarries filtrate from medulla to renalpelvisUrine formation by concentratingfiltrateRegulates amount of NaCl in urineReabsorption of NaCl by active transportEpithelium is permeable to water but notto saltNaClureawater

6. Collecting duct Duct is permeable to urea only in innermedulla Urea can diffuse out to the interstitial fluiddue to high urea concentration in filtrate Contribute to hyperosmotic environment Drives reabsorption of water by osmosis any urea and urine that is reabsorbedis less than that was filtered intonephron Filtrate becomes increasinglyconcentrated Enables conservation of water

Nutrient FlowSolute ProximaltubuleLoop ofHenleDistaltubuleCollectingductwater R R (desc) RNaCl R R (ascn) RH+S SHCO3- R Rglucose R Ramino acids R Rvitamins / minerals R Rurea / uric acid S S

Nutrient FlowSolute ProximaltubuleLoop ofHenleDistaltubuleCollectingductwater R R (desc) R RNaCl R R (ascn) R RH+S SHCO3- R Rglucose R Ramino acids R Rvitamins / minerals R Rurea / uric acid S S R

Urine ConcentrationFig. 44.23

Video Summarizing FunctionReview of excretory system http://www.youtube.com/watch?v=WtrYotjYvtU (12:21,start at 2:54 for focus on kidney)

Excretory System - structure function

by thelawofscience on May 28, 2012

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