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 lighter-colored outer part of the kidney is the renal cortex. The darker inner part is the renal medulla. Blood is filtered in the renal cortex and medulla to form urine. Within the kidney, urine travels through many structures before it reaches the ureter. The renal medulla contains dark triangular areas of tissue called the renal pyramids. Urine flows through a renal pyramid and exits at the renal papilla, the tip. The renal papilla has collecting ducts, small openings that allow urine to pass through.