Explain the mechanism of formation of concentrated urine in mammals.

(N/A) The formation of concentrated urine in mammals is primarily achieved through the $Counter-Current$ $Mechanism$ involving the $Loop$ $of$ $Henle$ and the $Vasa$ $Recta$.
$1$. $Counter-Current$ $Multiplier$: The $Loop$ $of$ $Henle$ creates a concentration gradient in the renal medulla. The descending limb is permeable to water but impermeable to electrolytes,while the ascending limb is impermeable to water but allows active transport of electrolytes ($Na^{+}$,$Cl^{-}$). This creates a hyperosmolar medullary interstitium.
$2$. $Counter-Current$ $Exchanger$: The $Vasa$ $Recta$ (capillary network surrounding the $Loop$ $of$ $Henle$) maintains this gradient by preventing the washout of solutes.
$3$. $Hormonal$ $Regulation$: Under the influence of $Antidiuretic$ $Hormone$ ($ADH$ or $Vasopressin$),the collecting duct becomes permeable to water. As the filtrate passes through the hyperosmolar medulla,water is reabsorbed into the blood via osmosis,resulting in the excretion of concentrated urine.