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FUNCTIONS OF KIDNEY



FUNCTIONS OF KIDNEY

excretory functionhomeostatic function

endocrine functionmetabolic function



E C!ETO!Y FUNCTION• This include formation and excretion

of urine"• The main ste# in$ol$ed are

– %lomerular &ltration – Tubular reabsor#tion – Tubular secretion



'

Filtration• !enal cor#uscle• Filtration membrane

– Fenestrated endothelium of ca#illaries – (asement membrane of )lomerulus – Slit membrane bet*een #edicels of

#odocytes



+



,

Forces that in-uence&ltration

• %lomerular blood hydrostatic#ressure

• O##osin) forces. – /lasma colloid osmotic #ressure – Ca#sular hydrostatic #ressure



0



1

%lomerular Filtration !ate• 2olume of #lasma &ltered 3 unit time• 4##rox" 516 7 3day•

Urine out#ut is about 58 9 7 3day• 4bout ::; of &ltrate is reabsorbed



:



56

%F! in-uenced by.• (lood #ressure and blood -o*• Obstruction to urine out-o*•

7oss of #rotein8free -uid• <ormonal re)ulation

– !enin = an)iotensin –

4ldosterone – 4D< – 4N/



55

>uxta)lomerular a##aratus• >uxta)lomerular cells lie in the *all of

a?erent arteriole• @acula densa in &nal #ortion of loo#

of <enle = monitor Na A and Cl 8 conc"and *ater

• Control blood -o* into the)lomerulus

• Control )lomerular &ltration



59



5B



5'

Tubular reabsor#tion• ater )lucose amino acids urea

ions• Sodium di?uses into cell acti$ely

#um#ed out = dra*in) *ater *ith it



5+



5,



50

• In addition to reabsor#tion also ha$etubular secretion = substances mo$efrom #eritubular ca#illaries intotubules = a second chance to remo$esubstances from blood"



51



5:

• (y end of #roximal tubule ha$ereabsorbed.

• ,68 06; of *ater and sodium• about 566; of )lucose and amino

acids• :6 ; of KA bicarb CaAA uric acid• Transport maximum = maximum

amount of a substance that can beabsorbed #er unit time

• Renal threshold = #lasma conc" of asubstance at *hich it exceeds Tm"



96

7oo# of <enle• !es#onsible for #roducin) a

concentrated urine by formin) aconcentration )radient *ithin themedulla of idney"

• hen 4D< is #resent *ater isreabsorbed and urine isconcentrated"

• Counter8current multi#lier



95



99

Distal con$oluted tubule andcollectin) ducts

• hat ha##ens here de#ends on 4D<• 4ldosterone a?ects NaA and KA•

4D< = facultati$e *ater reabsor#tion• /arathyroid hormone = increases CaAA reabsor#tion



9B



9'

Distal con$oluted tubule andcollectin) ducts

• Tubular secretion to rid body ofsubstances. KA <A ureaammonia creatinine and certaindru)s

• Secretion of <A hel#s maintainblood #<Gcan also reabsorb bicarb and)enerate ne* bicarbH



9+



<omeostatic Functions of UrinarySystem

1. Regulate blood volume and blood pressure: – by adjusting volume of water lost in urine – releasing erythropoietin and renin

2. Regulate plasma ion concentrations: – sodium #otassium and chloride ions Gby

controllin) uantities lost in urineH – calcium ion le$els



3. Help stabilize blood pH: – by controllin) loss of hydro)en ions and

bicarbonate ions in urine

4. Conserve valuable nutrients: – by #re$entin) excretion *hile excretin) or)anic

*aste #roducts

5. ssist liver to detoxi!" poisons



ENDOC!INE FUNCTIONSJKidneys ha$e #rimary endocrine function since they#roduce hormones

In addition the idneys are site of de)radation for

hormones such as insulin and aldosterone"In their #rimary endocrine function the idneys#roduce erythro#oietin renin and #rosta)landin"

#r"thropoietin is secreted in res#onse to a lo*eredoxy)en content in the blood" It acts on bone marro*stimulatin) the #roduction of red blood cells"



Renin $ the #rimary stimuli for renin releaseinclude reduction of renal #erfusion #ressureand hy#onatremia" !enin release is alsoin-uenced by an)iotension II and 4D<"

It is a ey stimulus of aldosterone release" The

e?ect of aldosterone is #redominantly on thedistal tubular net*or e?ectin) an increase insodium reabsor#tion in exchan)e for

#otassium" The idneys are #rimarily res#onsible for#roducin) $itamin DB from

dih"drox"cholecalci!erol



@ET4(O7IC FUNCTION• Kidney #erform )luconio)enesis

durin) #eriods of star$ation"


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