Indicate whether the following statement is true or false:
Henle's loop plays an important role in concentrating the urine.

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

Salmon have gills that are more permeable to water than to salts. Salmon hatch in fresh water streams and then migrate to the ocean. Once they reach the ocean,you would expect the rate of uptake of water into their body through the gills to:

Which of the following plays a significant role in maintaining the high osmolarity of the medullary interstitial fluid?

Assertion : In the descending limb of the loop of Henle,the urine is hypertonic,whereas in the ascending limb of the loop of Henle,the urine is hypotonic.
Reason : The descending limb is impermeable to sodium,while the ascending limb is impermeable to water.

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