Nephron Portion Reabsorbed Secreted Mechanisms Of Reabsorption Apical Basal/

Nephron Portion

Proximal Tubule

Loop of Henle • Thin Descending

Reabsorbed

Secreted

Mechanisms of Reabsorption Apical Basal/ Lateral

Na+, Cl-, HCO3-, K+, H2O, Glucose, aa’s

H+, Organic acids and bases

-Na/H exchanger -Bicarb buffer system

H2O Only

None

-Reabsorption 2° to cortical medullary urea gradient

•

Thin Ascending

Na+ (passive)

Urea

•

Thick Ascending

Na+, Cl-, K+, Ca2+, Mg2+, HCO3-

H+

-Na/K ATPase -HCO3diffusion

Major Characteristics

-65% H2O, Na+, K+, Urea reabsorbed -100% glucose, aa, protein reabsorbed -H2O passively follows Na+ – Isosmotic reabsorption -Concentrates tubular fluid

-Na/K ATPase -K+ channel -Cl- channel

-Impermeable to H2O -Dilutes tubular fluid -Impermeable to H2O -Dilutes tubular fluid -Na/K/2Cl cotransporter major transporter ~20% NaCl reabsorbed – inhibited by furosemide

-NaCl transporter

-Na/K ATPase -Cl- channel

-Impermeable to H2O, Urea -NaCl transporter inhibited by thiazides

-ENaC channel -K+ channel (secretion)

-Na/K ATPase -Cl- channel

-EnaC blocked by Amiloride - Na/K ATPase regulated by Aldosterone – Aldosterone inhibited by spironolactone -Permeable to H2O only in presence of ADH -Permeable to H2O in presence of ADH -Permeable to Urea -Can actively secrete H+

-Na/K/2Cl cotransporter -Na/H exchanger -Lumen +potential drives paracellular reabsorption Na+,K+,Mg2+,Ca 2+

+

-

2+

2+

Early Distal Tubule

Na , Cl , Ca , Mg

Late Distal Tubule and Cortical Collecting Duct • Principal Cells

Na+, Cl-

K+

H2O (+ADH only), HCO3-, K+ Na+, Cl-, Urea, HCO3-, H2O (+ADH only)

H+

•

Intercalated Cells

Medullary Collecting Duct

H+