Isotopes when written out are common nouns, and should begin with the uncapitalized element name, followed by a hyphen (not an em dash or en dash) and then the mass number. Examples are carbon-14 and uranium-235.
The central region of the kidney contains the renal pelvis, which is located in the renal sinus, and is continuous with the ureter. The renal pelvis is a large cavity that collects the urine as it is produced. The periphery of the renal pelvis is interrupted by cuplike projections called calyces.
The renal medulla is the interior portion of the kidney where the primary functions of the organ occur: the filtering of waste materials and elimination of fluid from the body. The kidney filters blood and sends waste materials to the bladder to become excreted urine. Inside the renal medulla are pyramids, each of which contains thousands of nephrons.