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 $HC{O}_3^{-}$ and hydrogen ions in $PCT$
(iv) Higher blood pressure in glomerular capillaries

• A. Only (ii)
• B. (iii) and (iv)
• C. (i), (ii) and (iii)
• D. (i) and (ii)

Answer 1

The correct option is D (i) and (ii)

Mammals have the ability to produce concentrated urine. The mechanism which facilitates production of concentrated urine is known as the counter current mechanism.

The Henle’s loop and vasa recta of the nephrons play a significant role in this.

The flow of filtrate in the two limbs of Henle’s loop and the flow of blood through the two limbs of vasa recta is in counter current pattern.

The proximity between the Henle’s loop and vasa recta, as well as the counter current in them helps in maintaining an increasing osmolarity towards the inner medullary interstitium.

Presence of such interstitial gradient helps in an easy passage of water from the collecting tubule thereby concentrating the urine.

Fig: counter current mechanism

Hence, option d is correct.

Selective secretion of $HC{O}_3^{-}$ and hydrogen ions in PCT helps to maintain the pH and ionic balance of the body fluids.

Higher blood pressure in glomerular capillaries facilitates the filtration of blood into the Bowman’s capsule.