Question

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 HCO₃^– and hydrogen ions in PCT

(iv) Higher blood pressure in glomerular capillaries

(1) (i) and (ii)

(2) Only (ii)

(3) (iii) and (iv)

(4) (i), (ii) and (iii)

Answer 1

Answer (1) (i) and (ii)

Sol. The correct answer is option (1) as both the statements (i) and (ii) are correct because counter current mechanism is based on special arrangement of Henle's loop and vasa recta and this mechanism maintain a concentration gradient in the medullary interstitium.

Statement (iii) is incorrect as PCT helps in selective secretion of H⁺, ammonia and K⁺ ions and reabsorption of HCO₃^– from it.

Statement (iv) i.e. blood pressure in glomerular capillaries is responsible for glomerular filtration and not for counter current mechanism.