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 pelvis is an important part of the kidney in humans and many animals that essentially acts as a filter for urine before it passes out of the kidney and into the bladder. It looks sort of like a cup-shaped open cavity, and it can usually expand or retract in response to urine volume.