The structure that separates the renal pyramids in the kidney is called the renal cortex.
The renal cortex is the outer part of the kidney and surrounds the inner medulla, which contains the renal pyramids. These pyramids are conical-shaped tissues that contain the nephrons, the functional units of the kidney responsible for filtering blood and producing urine. The renal cortex not only provides structural support to the pyramids but also houses the renal corpuscles and convoluted tubules, which are essential for the filtration and absorption processes in urine formation.
In summary, the renal cortex serves as the distinguishing boundary that separates the renal pyramids, playing a crucial role in the organization and function of the kidney.