Page 1042 - Fundamentals of anatomy physiology

Tubular fluid 4
from cortical
nephrons The thick ascending limb is
H2O impermeable to water and
solutes. The tubule cells actively
K+ 100–300 transport Na+ and Cl– out of the
A tubule, thereby decreasing the
Na+Cl– Na+ osmotic concentration of the
tubular fluid. Because only
300 Na+ and Cl– are removed, urea
makes up a higher proportion
Na+Cl– H2O of the total osmotic concentra-
Na+Cl– Na+ tion at the end of the nephron
Na+Cl– loop.
600 A
Na+Cl– K+ 5

900 600 Further adjustments in the
Na+Cl– composition of the tubular
H2O fluid occur in the DCT and the
collecting system. The osmotic
H2O concentration of the tubular
fluid can be adjusted through
ADH- active transport (reabsorption
regulated or secretion).
permeability
6
H2O 900
The final adjustments in the
H2O volume and osmotic concentra-
tion of the tubular fluid are
Nephron made by controlling the water
loop permeabilities of the distal
1200 H2O portions of the DCT and the
collecting system. ADH levels
Vasa determine the final urine
recta concentration.

7

The vasa recta absorbs the
solutes and water reabsorbed
by the nephron loop and the
collecting ducts. By transport-
ing these solutes and water into
the bloodstream, the vasa recta
maintain the concentration
gradient of the renal medulla.

1200 1200
1200

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