Counter current multiplier system is primarily driven by ?

Ans. is 'a' i.e., Concentration of Na+Countercurrent multiplierThe loop of HenleQ gives the nephron a peculiar shape. The descending limb, in which the tubular fluid flows towards the hairpin bend (downwords) and the ascending limb, in which the tubular fluid flows 'upwards' lie close to each other. Two such tubes with fluid flowing through them in opposite directions provide an oppounity for the countercurrent multiplication.The thick ascending limb of loop of Henle is impermeable to water but it actively reabsorbs NaCI. The thin descending limb of loop of Henle is relatively impermeable to solutes but highly permeable to water. The most impoant cause of the high medullary osmolarity is active transpo of sodiumQ and co-transpo of potassiumQ, chlorideQ and other ions out of the thick ascending limb of loop of HenleQ into the medullary interstitium. Most impoant among all these is NaClQ, for maintenance of high medullary interstitium.Consider the Na+ is continuously flowing in from glomerulus into the tubule. However, most of the Na+, instead of flowing out, gets trapped in a circular path and recycles between the ascending and descending limbs of the loop of Henle. Consequently, the Na+ concentration becomes very high at the tip of the loop.