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