Mammals have the ability to produce

If the Loop of Henle were absent from the mammalian nephron,which of the following is to be expected?

Select the correct option:
$(1)$ The counter-current mechanism is maintained by the Loop of Henle and the vasa recta.
$(2)$ The ascending limb of the Loop of Henle is impermeable to water.

The counter-current multiplier system changes the isotonic glomerular filtrate into

Explain the mechanism of formation of concentrated urine in mammals.

Why is a small amount of urea retained in the kidney matrix?