Some waste goes into the blood while most of it is left in the bowels. The urinary system and the kidneys keep the water and the chemicals in balance by cleaning up "urea" from the blood. Urea is the name given to wastes produced when certain foods like meat, poultry, and some vegetables are digested. The blood stream carries the urea into the kidneys.

The kidneys are two purple-brown organs that are located below the ribs. The purpose of the kidneys is to clean the urea from the blood and convert it into urine, maintain a balance between salts and other blood chemicals, and produce the erythropoietin hormone that helps with the production of red blood cells.

The kidneys contain small filters known as nephrons that extricate urea from the blood. Urea passes through the nephrons along with water and other wastes and gets converted into urine. There are two ureters, one for each kidney, that are basically narrow tubes providing a passageway for the urine from the kidneys to the bladder.

The ureter tube muscles are always tightening and loosening in a flexing motion that pushes the urine away from the kidneys and towards the bladder. Any trouble with the ureter tubes will halt urine flow leading to kidney infection. Urine is being constantly pushed down by the ureters every 10-15 seconds.

The bladder is triangular, hollow, and located in the lower abdomen. Ligaments hold it place by attaching to pelvic bones and other organs. The bladder has a limited flexibility to expand in order to store urine. The muscles in the bladder wall contract and flatten during urination.

A healthy adult bladder can store nearly two cups of urine from 2-5 hours. The bladder opening has two muscles known as sphincter muscles. These circular muscles act just like tight rubber bands around the bladder mouth and prevent any urine leakage. The bladder is provided with nerves that alert the individual when it is time to urinate.

The urethra is the tube that allows urine to exit the body. The normal urination process is the nerve signal generated by the bladder to the brain that causes the brain to order the bladder muscles to contract and the sphincter muscles to relax, squeezing the urine out of the bladder and out through the urethra.

Depending the type and quantity of fluids consumed in one day, adults may pass approximately 1 and one half quarts of urine in a 24 hour period. The quantity of urine produced in daytime is nearly double the quantity produced at night. In a normal human body, urine is sterile. It contains no bacteria, virus, or fungi, only fluids, salts, and waste products.