What is the Kidney? The kidneys are two bean-shaped organs that are located in the back of the abdomen, and that have many important functions essential for life. Among the most important are filtrating the blood, removing waste products from the blood and ensuring that the electrolytes within the blood are correctly balanced. In addition, the kidneys produce erythropoietin, a hormone responsible for the production of (the oxygen carrying) red blood cells. Each of the kidneys can be divided into two main functional parts. The outer region of the kidney is called the cortex The cortex consists of a series of tubes (called collecting tubules) and is responsible for the filtration of blood.. The inner region of the kidney is called the renal pelvis. The renal pelvis contains medullary pyramids that collect the filtrate (urine) from collecting tubules in the cortex and send it through the ... read more on Kidney Cancer: The Basics