The nephrons and their ampulla move away from the hilum. Due to this 'segregation', two zones can be distinguished in the kidney: a cortex (cortex renalis) with the nephrons, and a medullary pyramid (medulla renalis) with the collecting tubes and the excretory ducts.
During the fetal period, up to 14 renal lobes (lobi renales) can be recognized. A renal lobe, or renculus, designates a medullary pyramid together with the corresponding coat-shaped cortical substance. This medullary pyramid always terminates, through its papilla, in a renal calix. Adjacent renal lobes share common cortical regions that extend to the vicinity of the renal pelvis as a renal column. In a newborn baby, the renal lobes are often still prominent (ren lobatus in extreme cases). The lobar borders later disappear, and the kidney acquires a mainly smooth surface.