1
Fig. 44-15
Key
ActivetransportPassivetransport
INNERMEDULLA
OUTERMEDULLA
H2O
CORTEX
Filtrate
Loop ofHenle
H2O K+HCO3–
H+ NH3
Proximal tubuleNaCl Nutrients
Distal tubule
K+ H+
HCO3–
H2O
H2O
NaCl
NaCl
NaCl
NaCl
Urea
Collectingduct
NaCl
SoluteGradientsandWaterConserva2on
• Urine
– Muchmoreconcentratedthanblood
• Thecoopera5veac5onandprecisearrangementoftheloopsofHenleandcollec5ngducts
– Largelyresponsiblefortheosmo5cgradientthatconcentratestheurine
• NaClandurea
– Contributetotheosmolarityoftheinters55alfluid,whichcausesreabsorp5onofwaterinthekidneyandconcentratestheurine
TheTwo‐SoluteModel(NaCl&Urea)• Intheproximaltubule
– Filtratevolumedecreases,butitsosmolarityremainsthesame
• Countercurrentmul2pliersysteminvolvingtheloopofHenle
– Maintainsahighsaltconcentra5oninthekidney
• Usingenergyinac5vetransportofNaCl
– InthickascendinglimbofLoH
• ThinlimblosesNaClbydiffusion
• Allowsforma5onofconcentratedurine
– Thissystemallowsthevasarectatosupplythekidneywithnutrients,withoutinterferingwiththeosmolaritygradient
• Duetocounterflowofbloodinvasarecta
2
• Thecollec5ngduct
– Conductsfiltratethroughtheosmolaritygradient
• Cortextooutermedullatoinnermedulla
• Morewaterexitsthefiltratebyosmosis
– Ureadiffusesoutofthecollec5ngductasittraversestheinnermedulla
• UreaandNaClformtheosmo5cgradientthatenablesthekidneytoproduceurinethatishyperosmo5ctotheblood
TheTwo‐SoluteModel
Fig. 44-16-1
Key
ActivetransportPassivetransport
INNERMEDULLA
OUTERMEDULLA
CORTEXH2O
300 300
300
H2O
H2O
H2O
400
600
900
H2O
H2O
1,200
H2O
300
Osmolarity ofinterstitial
fluid(mOsm/L)
400
600
900
1,200
Fig. 44-16-2
Key
ActivetransportPassivetransport
INNERMEDULLA
OUTERMEDULLA
CORTEXH2O
300 300
300
H2O
H2O
H2O
400
600
900
H2O
H2O
1,200
H2O
300
Osmolarity ofinterstitial
fluid(mOsm/L)
400
600
900
1,200
100
NaCl
100
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
200
400
700
3
Fig. 44-16-3
Key
ActivetransportPassivetransport
INNERMEDULLA
OUTERMEDULLA
CORTEXH2O
300 300
300
H2O
H2O
H2O
400
600
900
H2O
H2O
1,200
H2O
300
Osmolarity ofinterstitial
fluid(mOsm/L)
400
600
900
1,200
100
NaCl
100
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
200
400
700
1,200
300
400
600
H2O
H2O
H2O
H2O
H2O
H2O
H2O
NaCl
NaCl
Urea
Urea
Urea
Mammals
• Thejuxtamedullarynephron
– Contributestowaterconserva5oninterrestrialanimals
• Mammalsthatinhabitdryenvironments
– HavelongloopsofHenle
• Whilethoseinfreshwaterhaverela5velyshortloops
BirdsandOtherRep2les• Birds
– HaveshorterloopsofHenle
• Eveninjuxtamedullarynephrons
• Butconservewaterbyexcre5nguricacidinsteadofurea
– Fairlynon‐watersolublesoexcretedasapaste
• Otherrep5leshaveonlycor5calnephrons
– Nojuxtamedullarynephrons
– Butalsoexcretenitrogenouswasteasuricacid
4
FreshwaterFishesandAmphibians
• Freshwaterfishes
– ConservesaltintheirDCT’s
• Excretelargevolumesofdiluteurine
• Kidneyfunc5oninamphibians
– Similartofreshwaterfishes
– Amphibiansconservewateronlandbyreabsorbingwaterfromtheurinarybladder
MarineBonyFishes
• Marinebonyfishes
– Hypoosmo5ccomparedwiththeirenvironmentandexcreteveryliSleurine
• Urealostthroughskinandgills
• Fewerandsmallernephronsthanfreshwaterfish
– NoDCT
– Divalentionssecretedtoproximaltubule
• Ca2+,Mg2+,SO42‐
HormonalControl• Mammals
– Controlthevolumeandosmolarityofurine
• ThekidneysoftheSouthAmericanvampirebat
– Canproduceeitherverydiluteorveryconcentratedurine
• Allowsquickweightloss
– Releasingwatermassindiluteurine
• Ordigestlargeamountsofproteinwhileconservingwater
– Excre5nghyperosmo5curea
5
An2diure2cHormone• Osmolarityofurine
– Regulatedbynervousandhormonalcontrolofwaterandsaltreabsorp5on
• An2diure2chormone(ADH)(vasopressin)
– Increaseswaterreabsorp5onintheDCTandcollec5ngducts
• AnincreaseinosmolaritytriggersthereleaseofADH,whichhelpstoconservewater
– Whenabove300mOsm/LAnimation: EffectAnimation: Effect of ADH of ADH
Fig. 44-19
Thirst
Drinking reducesblood osmolarity
to set point.
Osmoreceptors inhypothalamus trigger
release of ADH.
Increasedpermeability
Pituitarygland
ADH
Hypothalamus
Distaltubule
H2O reab-sorption helpsprevent further
osmolarityincrease.
STIMULUS:Increase in blood
osmolarity
Collecting duct
Homeostasis:Blood osmolarity
(300 mOsm/L)
(a)
Exocytosis
(b)
Aquaporinwaterchannels
H2O
H2O
Storagevesicle
Second messengersignaling molecule
cAMP
INTERSTITIALFLUID
ADHreceptor
ADH
COLLECTINGDUCTLUMEN
COLLECTINGDUCT CELL
• Muta5oninADHproduc5oncausesseveredehydra5on
– Resultsindiabetesinsipidus
• Largevolumesofdiluteurine
• Alcoholisadiure5casitinhibitsthereleaseofADH
An2diure2cHormone
6
TheRenin‐Angiotensin‐AldosteroneSystem• Renin‐angiotensin‐aldosteronesystem(RAAS)
– Partofacomplexfeedbackcircuitthatfunc5onsinhomeostasis
• Adropinbloodpressureneartheglomerulus
– Causesthejuxtaglomerularapparatus(JGA)toreleasetheenzymerenin
• Renintriggerstheforma5onofthepep5deangiotensinII
• AngiotensinII
– Raisesbloodpressureanddecreasesbloodflowtothekidneys
• Throughvasoconstric5on
– S5mulatesthereleaseofthehormonealdosterone
• Causesreten5onofsalt
• Increasesbloodvolumeandpressure
TheRenin‐Angiotensin‐AldosteroneSystem
Fig. 44-21-1
Renin
Distaltubule
Juxtaglomerularapparatus (JGA)
STIMULUS:Low blood volumeor blood pressure
Homeostasis:Blood pressure,
volume
7
Fig. 44-21-2
Renin
Distaltubule
Juxtaglomerularapparatus (JGA)
STIMULUS:Low blood volumeor blood pressure
Homeostasis:Blood pressure,
volume
Liver
Angiotensinogen
Angiotensin I
ACE
Angiotensin II
Fig. 44-21-3
Renin
Distaltubule
Juxtaglomerularapparatus (JGA)
STIMULUS:Low blood volumeor blood pressure
Homeostasis:Blood pressure,
volume
Liver
Angiotensinogen
Angiotensin I
ACE
Angiotensin II
Adrenal gland
Aldosterone
Arterioleconstriction
Increased Na+
and H2O reab-sorption in
distal tubules
Homeosta2cRegula2onoftheKidney
• ADHandRAAS
– Bothincreasewaterreabsorp5on
• ButonlyRAASwillrespondtoadecreaseinbloodvolume
• Atrialnatriure2cpep2de(ANP)
– OpposestheRAAS
– ANPisreleasedinresponsetoanincreaseinbloodvolumeandpressure
• Inhibitsthereleaseofrenin
8
Fig. 44-UN1Animal
Freshwaterfish
Bony marinefish
Terrestrialvertebrate
H2O andsalt out
Salt in(by mouth)
Drinks water
Salt out (activetransport by gills)
Drinks waterSalt in H2O out
Salt out
Salt in H2O in(active trans-port by gills)
Does not drink water
Inflow/Outflow Urine
Large volumeof urine
Urine is lessconcentratedthan bodyfluids
Small volumeof urine
Urine isslightly lessconcentratedthan bodyfluids
Moderatevolumeof urine
Urine ismoreconcentratedthan bodyfluids
Youshouldnowbeableto:
1. Dis5nguishbetweenthefollowingterms:isoosmo5c,hyperosmo5c,andhypoosmo5c;osmoregulatorsandosmoconformers;stenohalineandeuryhalineanimals
2. Defineosmoregula5on,excre5on,anhydrobiosis
3. Comparetheosmoregulatorychallengesoffreshwaterandmarineanimals
4. Describesomeofthefactorsthataffecttheenerge5ccostofosmoregula5on
5. Describeandcomparetheprotonephridial,metanephridial,andMalpighiantubuleexcretorysystems
6. Usingadiagram,iden5fyanddescribethefunc5onofeachregionofthenephron
7. ExplainhowtheloopofHenleenhanceswaterconserva5on
8. Describethenervousandhormonalcontrolsinvolvedintheregula5onofkidneyfunc5on
