The region of the kidney with the lowest solute concentration is actually the cortex. This is a section where a part of the distal convoluted tubule and the proximal convoluted tubule is found. The concentration of the solute grows on the increase as one slope into the medulla, and you can found concentrated urine in the renal pelvis.
Actually, when it comes to the field of zoology and anatomy, the cortex is the superficial or outermost layer of an organ. The organs that have these well-defined cortical layers are kidneys, ovaries, portions of the brain like the cerebral cortex, the thymus, and adrenal glands.
There are also just three main regions of the kidney and these are the renal medulla, renal pelvis, and renal cortex. The inner part is the renal medulla, while the outer part is the renal cortex. This outer part is the place where blood is being filtered.