Urine present in the duct of Bellini is

Collecting ducts merge into ducts of Bellini. These are also called papillary ducts. They concentrate and transport urine from the nephrons to larger ducts that connect with the renal calyces. Thus, urine present in the duct of Bellini is hypertonic to blood plasma. 

The permeability of the medullary collecting duct to water is controlled by the level of ADH. With high levels of ADH, water is avidly reabsorbed into the medullary interstitium, thereby reducing the urine volume and concentrating most of the solutes in the urine.