[Solved] The music industry reports that illegal downloading of music and videos is a growing problem. Microscopic Units: Small units of measurement typically used to describe dimensions of cells and microorganisms, not visible to the naked eye. Calyx: The cuplike division of the kidney pelvis. Medulla: A central region of an organ, notably in the brain (medulla oblongata) affecting vital functions like breathing and heart rate, and in the kidney involved in regulating electrolyte balance. Renal Papillae: The apex of the renal pyramid, which projects into the renal pelvis and where urine flows into the ureter.