Which region of the kidney is the outermost layer?

The renal cortex is the outermost layer of the kidney. This region plays a crucial role in the kidney's function, as it contains a large number of nephrons, which are the functional units responsible for filtering blood and forming urine. The cortex is rich in blood vessels and is essential for the initial stages of filtration and reabsorption processes that occur in the kidneys.

In contrast, the renal pelvis is located deeper in the kidney and acts as a funnel for urine flowing into the ureter. The renal medulla is also deeper, consisting mainly of the renal pyramids that contain the collecting ducts and loop of Henle, which are involved in the concentration of urine. The term "nephron zone" is not commonly used as a distinct anatomical term within kidney structure; rather, it encompasses the functional aspects of the nephron within the renal cortex and medulla.

Thus, the renal cortex is clearly identified as the outermost layer of the kidney.