The Vertical Osmotic Gradient in the Kidney

Multiple Choice

The vertical osmotic gradient in the kidney

A) is established and maintained by the countercurrent system.
B) makes it possible to put out urine of variable concentration depending on the needs of the body by varying the degree of water permeability of the distal portions of the nephron.
C) is found in the renal cortex.
D) both (a) and (b) above.
E) all of these answers.