Hello,

• The counter current mechanism takes place in Juxtamedullary nephron.
• The function of the countercurrent multiplier is to produce the hyperosmotic Medullary Interstitium.
• The ADH promotes water reabsorption through the walls of the distal convoluted tubule and collecting duct.
• Urea reabsorbed from collecting duct to medullary interstitum produces the hyperosmotic Medullary interstitium.
• Reabsorption of urea will occur in the presence of ADH.
• Excretion of large volume or small volume of urine won’t affect the rate of solute excretion.
• Nephrogenic diabetes insipidus patients will have no response from the kidney to ADH.
• The function of the Countercurrent exchanger “vasa recta” is to maintain hyperosmolar medulla.

The production of concentrated urine is achieved by osmotic equilibration of the collecting duct luminal fluid with the hypertonic medullary interstitium. Urinary concentration is achieved by countercurrent multiplication in the inner medulla. The single effect in the outer medulla is active NaCI absorption from the thick ascending limb. While the single effect in the inner medulla is not definitively established, the majority of experimental data favors passive NaCI absorption from the thin ascending limb. Continued experimental studies in inner medullary nephron segments will be needed to elucidate fully the process of urinary concentration.

Best Wishes.