Hyperosmolarity of renal medulla is due to

The renal medulla is the innermost pa of the kidney. The renal medulla contains the structures of the nephrons responsible for maintaining the salt and water balance of the blood. These structures include the vasa rectae, the venulae rectae, the medullary capillary plexus, the loop of Henle, and the collecting tubule. The renal medulla is hypeonic to the filtrate in the nephron and aids in the reabsorption of water.Ref: Ganong&;s Review of Medical Physiology; 24th edition; page no: 671