question_answer 4)

Give a brief account of the counter current mechanism. 

Answer:

Counter-Current Mechanism (See Text) (i) The counter current mechanism takes place in Henle's loop and vasa ' recta. (ii) The flow of filtrate in the two limbs of Henle's loop is in opposite directions and thus, forms a counter-current. (iii) The flow of blood through the two limbs of vasa recta is also in a counter current pattern. (iv) NaCI is transported by the ascending limb of Henle's loop which is exchanged with the descending limb of vasa recta. (v) NaCI is returned to the interstitium by the ascending portion of vasa recta. (vi) Similarly, small amount of urea enter the thin segment of the ascending limb of Henle's loop, which is transported bach to the interstitium by the collecting tubule. (vii) This transport of substances facilitated by the special arrangement of Henle's loop and vasa recta is called the counter current mechanism. (viii) It helps to maintain a concentration gradient in the medullary interstitium. Which facilitates an easy passage of water from the collecting tubule thereby concentrating the filtrate (urine).