<prompt> Formation of a small volume of concentrated urine in dehydration is associated with:More reabsorption in the PCTMore concentration in loop of HenleMore reabsorption of DCT and collecting ductsAll of these  <response>: In the presence of enough vasopressin to produce maximal antidiuresis, water moves out of the hypotonic fluid entering the cortical collecting ducts into the interstitium of the cortex, and the tubular fluid becomes isotonic. In this manner, as much as 10 of the filtered water is removed. The isotonic fluid then enters the medullary collecting ducts with a TFP inulin of about 20.An additional 4.7 or more of the filtrate is reabsorbed into the hypertonic interstitium of the medulla, producing a concentrated urine with a TFP inulin of over 300. In humans, the osmolality of urine may reach 1400 mOsmkg of H2O, almost five times the osmolality of plasma, with a total of 99.7 of the filtered water being reabsorbed.The basic requirements for forming a concentrated urine are:A high level of ADH, which increases the permeability of the distal tubules and collecting ducts to water, thereby allowing these tubular segments to avidly reabsorb water. A high osmolarity of the renal medullary interstitial fluid, which provides the osmotic gradient necessary for water reabsorption to occur in the presence of high levels of ADH.Reference: Ganongs Review of Medical Physiology T W E N T Y - F I F T H E D I T I O N page no 685, Guyton physiology 13th ed page no 374 