Renal Transport

8/10/2019 Renal Transport

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NaCl and water reabsorption

Along the nephron

OBJECTIVES

1.Explain the three processes involved in the production of

urine

a. filtration b. reabsorption c. secretion.

2.Describe the magnitude of the processes of filtration and

reabsorption by the nephron.

3.Describe the composition of normal urine.

4.explain the basic transport mechanisms present in each

nephron segment.5.Describe how water reabsorption is coupled to Na+

reabsorption in the proximal tubule.

6.Explain how solutes, but not water , are reabsorbed by the

thick ascending limb of Henlesloop.


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OBJECTIVES

7. Describe how Starling forces regulate solute and

water reabsorption across the proximal tubule.

8. Explain glomerulotubular balance and its physiological

significance.9. Identify the major hormones that regulate NaCl

and water reabsorption by its nephron segment


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COMPOSITION OF URINE


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Mechanisms Of Solute Transport

PASSIVESpontaneous, down an electrochemical gradient

No energy requirement

Diffusion Facilitated diffusion

Antiport Symport

Ion channel Uniport Coupled transport


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ACTIVE

Againstan electrochemical gradient

Requires direct input of energy

Active transport Endocytosis.


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Tubuler fluid

Paracelluler

pathway

Transcelluler

pathway

Tight

junction

Apical cell

membrane

Lateral intercellular space

blood

Na+

K+

Na+

Na+

Basolateralmembrane

Capillary

Basement

membrane

ATP

ATP

ATP


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Lateral

intercellularspace

Apical cellmembrane


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Tubular fluid

blood

Na+

X

Na+H+

HCO3

K+

Na+ATP

X

CO2 + H2O

CA

First half of proximal tubule


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Tubular fluid

blood

NaCl

H2O

Na+

Cl-

orga

nics

H2O

0rganics Na+ Cl-

org

anic Na+ Cl-

organics Na+ Cl-

H2O


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Tubular fluid

CL-

Na+

Na+ Na+ Na+

H+Hbase

Base

Cl-

Cl-

Na+

Cl-

H base

K+ATP

K+

Cl-

blood

Second half of proximal tubule


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Some organic secreted by the proximal tubule

Endogenous anions Drug

cAMP acetazolamide

Bile salts chlorothiazide

Hippurate(PAH) furosemide

Oxalate penicillin

Prostaglandins probenecid

Urate salicylate(aspirin)

hidrochlorthiazidebumetanide


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Some organic cations secreted by the proximal tubule

Endogenous cations Drugs

Creatinine atropine

Dopamine isoproterenolEpinephrine cimetidine

Norepinephrine morphine

quinine

amiloride


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Tubular fluid

A-

PAH

OA-

Na+

K+

Na+

Di/tri carboxylaseDi/tri carboxylase

PAH(OA-)

ATP

BLOOD


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HENLES LOOP

-Reabsorbs approimately 20 % of filtered Na+, Cland K+

-Ca+, HCO3- and Mg++

-Exclusively in the thick ascending limb

-The ascending thin limb and descending thin limb does not

reabsorbs.

-water is reabsorbed exclusively in the descending thin limb

-The ascending limb is impermiable to water


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Tubulalar fluidblood

Paracellulardiffusion

Na+

2Cl-

K+

Na+

K+

H+CO2 + H2O HCO3

Cl-

K+

Na+

K+ ATPCA

Na+K+

Ca++

MG++

H2O

+


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DISTAL TUBULE AND COLLECTING DUCT

Reabsorb approximately 12 % of the filtered Na+ and Cl-

Secrete variable amount of K+ and H+

The first segment: reabsorbs Na+.Cl- and Ca++ and its im-

permiable to water.The last segment of distal tubule and collecting duct: reabsorb

ed Na+ and water and secrete K+(princial cell)

Intercalated cell secrete H+ and reabsorb HCO3- and K+


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Tubularfluid

blood

DISTAL TUBULE AND

COLLECTING DUCT

Principal cellNa+

K+

Na+

K+ATP


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Tubularfluid

blood

H+ HCO3

Intercalated cell

CO2 + H2O

CAATP


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REGULATION OF NaCL AND WATER

REABSORPTION

Tubularfluid

bloodInterstitialspace

Basement

membrane

1

3

2

IIcapP cap

P is

II is

S G O


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Tubular

fluidblood

Na+

Cl-

H2O

Na+

Cl-

K+ATP

EARLY SEGMENT OF

THE DISTAL TUBULE


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1. STARLING FORCES

2. GLOMERULOTUBULAR BALANCE

3. HORMONES

4. SYMPHATIC NERVOUSN SYSTEM


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HORMONES that regulate NaCl and water reabsorption

SEGMENT HORMONE EFFECTS

Prox.tubule angiotensin II NaCl H2O

glucocorticoids NaCl H2O

Thick Asc. Aldosteron NaCllimb vasopressin NaCl

Distal Tub./ aldosteron NaCl

Collecting Duct atrial natriuretic Pep. NaCl H2Oprostaglandin NaCl H2O

bradikynin NaCl

vasopressin NaCl H2O

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Renal Transport