The shape of vasa recta is

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

$A$: The final reabsorption of water from urine into blood occurs through the collecting duct of a mammalian nephron,resulting in the production of hyperosmotic urine.
$R$: The loop of Henle is responsible for the formation of a sodium gradient across the depth of the medullary interstitium of a mammalian kidney.

Urine is concentrated in which part of the nephron?

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.

We can produce a concentrated urine. This is facilitated by a special mechanism. Identify the mechanism.