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

The increase in osmolarity from outer to inner medullary interstitium is maintained due to:
$(i)$ Close proximity between Henle's loop and vasa recta
$(ii)$ Counter current mechanism
$(iii)$ Selective secretion of $HCO_{3}^{-}$ and hydrogen ions in $PCT$
$(iv)$ Higher blood pressure in glomerular capillaries

Urine is concentrated in which part of the nephron?

In vertebrates,the ability to produce concentrated urine is generally associated with the ............ .

In the given diagram,what are the regions $P, Q,$ and $R$?
$P \quad\quad Q \quad \quad R$

In the nephron, the transport of substances like sodium chloride and urea is facilitated by a special arrangement called the counter-current mechanism, which comprises of: