Nefron & Pembentukan Urin 2013

8/18/2019 Nefron & Pembentukan Urin 2013

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dr. Huda Marlina Wati

Nefron dan Pembentukan Urin


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Structure of Urinary Tract


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Nephron is the functional unitof the kidney

Each kidney consists of about 1 million microscopicfunctional units known as nephrons, which arebound together by connective tissue.

Recall that a functional unit is the smallest unitwithin an oran capable of performin all of thatoran!s functions.

"he arranement of nephrons within the kidneys

two distinct reions #$ an outer reion %renal cortex”, look s ranular&& an inner reion' the renal medulla striatedtrianles' the renal pyramids


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Each nephron consists of a vascularcomponent and a tubular component

vascular component

• Aerent arteriole

• Glomerular

• Eerent arteriole

• eritubularcapillaries

tubular component

• !owman"s capsule

• roximal tubule

• #oop of $enle

• %istal tubule &collecting duct

'ombined vascular(tubular component

)uxtaglomerular apparatus (unction # produce substances in)ol)ed in the

control of kidney function


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Juxtaglom: is one component of an important feedback mechanism

that is involved in the autoregulation of RBF and FR


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(ormation of urin

*he three basic renalprocesses

+ glomerular -ltration,

. tubular reabsorption, and

/ tubular secretion


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*lomerular (iltration

Normally' about +,- of the plasma that enters thelomerulus is ltered.

the -rst step in urine formation

+.0 ml ( minute of lomerular ltrate are formed

"his means+12 liters(each day.

"his means that the kidneys ounts to lter the entireplasma )olume about 30 times per day

/f e)erythin ltered passed out in the urine' the totalplasma )olume would be urinated in less than half anhour0

*his does not happen' because the kidney tubulesand peritubular capillaries' materials can be

transferred between the uid inside the tubules and


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*lomerular capillary blood pressure

/s the ma2or force that causes lomerularltration

No local enery is used to mo)e uid fromthe plasma across lomerular membrane to3owman!s capsule

assive physical forces similiar actingacross capillaries elsewhere, e4cept .important dierence #

1. *lomerular capillaries are more permeablethan capillaries elsewhere

+. "he balance of forces across lomerular

membrane occurs the entire lenth of the


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(orces in)ol)ed in lomerularltration

5 physical forces #

1. *lomerular capillary blood pressure

6epends on contraction of the heart andresistance of the blood 788 mmH9

+. Plasma&coloid osmotic pressure

tendency for H+: to mo)e by osmosisfrom 3owman!s capsule into lomerulus75, mmH9

5. 3owman!s capsule hydrostatic pressure71, mmH9

tends to push uid out of 3owman!scapsule


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Glomerular 4iltration 5ate

net -ltration pressure 6 +2 mm$g 7008 7/2 9 +0 mm$g:

G45, depends not only on the net ltrationpressure' but also on how muchglomerular surface area

Properties of the lomerular membrane arecollecti)ely referred to as the - ltrationcoe;

cient 7Kf).

G45 6 Kf x net ltration pressure

*(R ; 1+8 ml


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'hanges in the G45 result primarily 6changes in glomerular capillary bloodpressure

Remember 00 net -ltration pressure

Plasma&colloid osmotic pressure and 3owman!s capsule

hydrostatic pressure are not sub2ect to reulation and' donot )ary much.

!ut, decrease in plasma protein concentration' by reducinthis pressure' leads to an increase in the G45 7ex !urn:

When plasma&colloid osmotic pressure is ele)ated' 7such as

dehydratin diarrhea9' the G45 is reduced. "he dammin up of uid behind the obstruction ele)ates

capsular hydrostatic pressure 7e4. Urinary tract obstruction9


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' @N *$EG45

; by controlled lomerular capillary bloodpressure to ad2ust the *(R to body needs

"he manitude of the lomerular capillary bloodpressure depends on the rate of blood ow

within each of the lomeruli.; mean systemic arterial blood pressure and the

resistance of a=erent arterioles

/f resistance increases' less blood ows into the

lomerulus' decreasing the G45

*wo maBor control mechanisms regulate the G45 C

+ Autoregulation

. Extrinsic symphatic control


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?E'$AN@>?> 5E>@!#E 4


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>utoreulation

"wo intrarenal mechanisms #(1) myogenic mechanism, respond to

change of pressure in nephron vascular

()7+9 tubuloglomerular feedback

mechanism, which senses changes in thesalt le)el

?yogenicmechanism•

?mooth muscle ofarteriole contractsin response tothe stretch

• >utomaticallyconstricts on its

*ubuloglomerularfeedback 7*G4: C• @nvolves the juxtaglomerularapparatus

• ?peciali@ed tubular

cells Dmaculadensa”


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u4 a omeru arapparatus


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"ubulolomerular (eedback7"*(9

/n response to the resultant rise in saltdeli)ery to the distal tubule' the maculadensa cells release A! and adenosine,both of which act locally as a paracrine on

the ad2acent a= erent arteriole' causin itto constrict

"o e4ert e)en more e4Buisite control o)ertubulolomerular feedback' the macula

densa cells also secrete the )asodilator'nitric oxide


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Extrinsicsymphatethiccontrol

E4trinsiccontrol of *(R'7sympatheticner)ous9 inputto the a= erentarterioles'7regulatingarterial

bloodpressure:

!aroreceptorreex


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R!U"#T$%& %F R!" B"%%' F"%(

hemorrhage

Arterial blood pressure

Intra renal receptors

Renin secretion

Plasma renin

Plasma angiotensin

Constriction of

Renal arterioles

RBF and GFR

Activity of renal

Symphatic nerves

Carotic sinus andAortic arch reflexs


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+. *ubular 5eabsorption &>ecretion

is a hihly selecti)e process

>ll constituents e4cept plasma proteinsare at the same concentration in the

lomerular ltrate as in plasmathe tubules ha)e a hih reabsorpti)e

capacity for substances needed by thebody and little or no reabsorpti)e capacity

for substances of no )alue*ubular reabsorption involves

transepithelial transport


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"ransepitelial transport


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A>>@E 5EA!>


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An active Na8F A*ase pump in the basolateralmembrane is essential for Na reabsorption

•

?odium reabsorption is uniue and complex.• :f the total enery spent by the kidneys' 12H is

used for Na transport


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Aldosterone stimulates Na reabsorptionin the distal and collecting tubules

A'*@A*@


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"he renin&aniotensin&aldosterone a4is. >niotensin //is a critical hormone in the control of blood pressure


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Renin

etika arteriol aferenmemasukilomerulus' sel otot

polos bermodikasimbtk f4 sekretori sel 2u4ta lomerulus.

?el 2u4talom C

makula densa msekresi renin' suatuenJim proteolitik.


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BrainA!

Angiotensin II

"ung Ang II

AdrenalAldosteron

#idney

$a% excretion

!&' excretion

Angiotensin I

Angiotensinogen

!epar

Renin

R##S


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Glucose and aminoacids are reabsorbedby NaKdependent

secondary activetransportNormally allglucose -lteredreabsorb in '*


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>ntiporters in Pro4imal tubule


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Passi)e rebsorption


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Some organic secreted by the proximal tubule

!ndogenous anions 'rug

cA(P aceta)olamideBile salts chlorothia)ide

!ippurate*PA!+ furosemide

'xalate penicillin

Prostaglandins probenecid

,rate salicylate*aspirin+

hidrochlorthia)ide

bumetanide


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Some organic cations secreted by the

proximal tubule

!ndogenous cations 'rugs

Creatinine atropineopamine isoproterenol

-pinephrine cimetidine

$orepinephrine morphine

.uinine amiloride

R b ti f F f


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Reabsorption of Foop ofHenle

G8 - water reabsorp by pro4imal tubule "he loop of Henle reabsorbs about 18- of

the ltered

water +,I5,- of the ltered Na and 58- of the ltered 1,I+,- of the lteredHJ:5 and a )ariable amount of theltered Ja+ and M+


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Jountercurrent Mechanism

/nteraction between the ow of ltratethrouh the loop of Henle 7countercurrentmultiplier9 and the ow of blood throuhthe )asa recta blood )essels

7countercurrent e4chaner9 "he solute concentration in the loop of

Henle ranes from 5,, m:sm to 1+,,m:sm

6issipation of the medullary osmoticradient is pre)ented because the blood inthe )asa recta eBuilibrates with theinterstitial uid


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Foop of Henle# JountercurrentMultiplier

"he descendin loop of Henle#/s relati)ely impermeable to solutes/s permeable to water

"he ascendin loop of Henle#

/s permeable to solutes

/s impermeable to water

Jollectin ducts in the deep medullaryreions are permeable to urea


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Foop of Henle# JountercurrentE4chaner

"he )asa recta is a countercurrent e4chanerthat#Maintains the osmotic radient

6eli)ers blood to the cells in the area

"nterActi#e !hysiology LC =rinary >ystemC Early 4iltrate

rocessing

PLAY


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Foop of Henle# JountercurrentMechanism

(iure +8.1D


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6istaltubule


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)%*+%S$T$%& %F UR$&!

SUBST#&)! )%&)!&TR#T$%&

$a% /0 1 2/0 me.3l

#% &0 1 40 me.3l

$!51 60 1 /0 me.3l

Ca%% / 1 2& me.3l (g%% & 1 27 me.3l

Cl 1 /0 1 260 me.3l

P'5 &0 1 50 me.3l

,rea &00 8 500 m(

#reatinin 9 1 &0 m(

p! / 1 4

'smolality /00 1 700 m'sm3#g !&'

others 0


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(ormation of 6ilute Urine

(iltrate is diluted in the ascendin loop ofHenle

6ilute urine is created by allowin thisltrate to continue into the renal pel)is

"his will happen as lon as antidiuretichormone 7>6H9 is not bein secreted


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(ormation of 6ilute Urine

Jollectin ducts remain impermeable towater no further water reabsorption occurs

?odium and selected ions can be remo)edby acti)e and passi)e mechanisms

Urine osmolality can be as low as 8, m:sm7one&si4th that of plasma9


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(ormation of Joncentrated


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(ormation of JoncentratedUrine

>6H&dependent water reabsorption is called

facultati)e water reabsorption>6H is the sinal to produce concentrated urine "he kidneys! ability to respond depends upon

the hih medullary osmotic radient

"nterActi#e !hysiology LC=rinary >ystemC #ate 4iltrate rocessing

PLAY

(ormation of 6ilute and


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(ormation of 6ilute andJoncentrated Urine

(iure+8.18a' b


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>elamat

!elaBar

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Nefron & Pembentukan Urin 2013