The proximity between the _______ and ________, as well as the ____________ in them help in maintaining an increasing osmolarity from 300 mOsmolL–1 in the ___________ (A) to about 1200 mOsmolL–1 in the _____________ (C). This gradient is mainly caused by _________ and ____________ .

Question

( a ) Henle’s loop and vasa recta; counter current ; cortex, inner medulla; NaCl and urea
( b ) Henle’s loop and vasa recta; counter current ; outer medulla, inner medulla; NaCl and HCO3-
( c ) collecting duct and vasa recta; counter current ; cortex, inner medulla; NaCl and urea
( d ) collecting duct and vasa recta; counter current ; medulla, cortex; NaCl and HCO3-