The kidneys are retroperitoneal bean shaped organs that lie in the paravertebral gutters, against the posterior abdominal wall. They lie at an oblique orientation with the upper poles more medial and posteriorfrom the lower poles They are located on each side of the spine; between T12-L4, and are embedded in perirenal fat. The right kidnet is usually slightly lower than the left do to displacement by the liver. Each kidneyis composed of an outer cortex and an inner medulla. The renal cortex comprises the outer 1/3 of the renal tissue and has extensions between the renal pyramids of the medulla. The cortex containsthe functional subunit of the kidneys called the nephron. The nephron consists of the glomerulus and connected tubules and is responsible for filtration of urine.