The structures of the urinary system include the kidneys, ureters, bladder, and urethra. Those that are located within the abdomen are the kidneys and ureters. The bladder and urethra are located in the pelvis. The kidneys are retroperitomal-been-shaped organs that lie against the posterior abdominal wall on either side of the vertebral column. They lie at an oblique orientation with the upper poles more medial and posterior than the lower poles. They are located on each side of the spine between T12 and L4 and are embedded in periornal fat. The right kidney is usually slightly lower due to displacement by the liver. The kidneys function to excrete waste, end products of metabolism, from the blood, form urine, and balance body fluids. The kidneys also have endocrine functions that include production and release of urethra opiatin, which stimulates the bones to make red blood cells, re-nin, which aids in regulating blood pressure, and the active form of vitamin D, which helps maintain calcium absorption, and mineral metabolism. Each kidney is composed of an outer cortex and an inner mediala. The renal cortex comprises the outer one-third of the renal tissue. The cortex contains the functional subunit of the kidney, the nephron, which consists of the glomerulus, and convoluted tubules, and is responsible for filtration of urine. The renal mediala consists of segments called renal pyramids that radiate from the renal sinus. The fat-filled cavity surrounding the renal pelvis, to the outer surface of the kidney. The striated appearing pyramids contain the loops of henna and collecting tubules and function, as the beginning of the collecting system. Arising from the renal papilla are the cup-shaped minor calisers. Each kidney has 7 to 14 minor calisers that merge into 2 or 3 major calisers. The major calisers join to form the renal pelvis, which is the largest elated portion of the collecting system, and is continuous with the urators. Surrounding the kidneys in peri-renal fat is another protective layer called the renal fascia. Gerotus fasciaed the renal fascia functions to anchor the kidneys to surrounding structures, in an attempt to prevent bumps and jolt to the body from injuring the kidneys. In addition, the renal fascia acts as a barrier, limiting the spread of infection that may arise from the kidneys. The medial indentation in the kidney is called the hilum. It allows the renal artery and vein and urators to enter an exit. The kidneys can be divided into 5 segments according to their vascular supply. Apical and Tarot superior upper anterior and Tarot inferior, Mibble inferior, inferior and posterior. The segmental classification helps with surgical planning for partial nephrectamies. The urators are paired muscular tubes approximately 10 to 12 inches in length, that transport urine to the urinary bladder. The upper half of the urators are within the abdomen and the lower half within the pelvis. Each urator originates at the renal pelvis and courses slightly anteriorly and medially and then descends the abdomen just anterior to the soas muscles. The urators then enter the posterior wall of the bladder at an oblique angle. Urine is excreted from the bladder through the urethra.