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Each kidney is comprised of a fibrous outer layer called the renal capsule, a peripheral layer called the cortex, and an inner layer called the medulla. The medulla is arranged in multiple pyramidal structures that together with overlying cortex comprise a renal lobe (red box). Urine drains from the tip of each pyramid (papilla) into minor and major calices that empty into the renal pelvis. The renal pelvis then transmits the urine to the bladder via the ureter. Nephrons are found within the cortex and medulla and have a characteristic structure that includes a glomerular blood filter containing podocytes and a tubular epithelium that loops down into the medulla. The tubule is subdivided into proximal, intermediate, and distal segments (see color key) that are important for the recovery and modification of the glomerular filtrate.