Blood enters the kidneys and goes through internal filters called nephrons, which separate it into minerals, solid material and waste material. Minerals return to the bloodstream for healthy body function, and urine is the waste material stored in the bladder until discharged during urination, according to Johns Hopkins.
Filtering about 120 to 150 quarts of blood daily, the kidneys are fist-sized organs shaped like beans. Located on both sides of the spine and below the ribcage, the kidneys generate about 1 to 2 quarts of urine from the amount of blood cycled through daily, states Johns Hopkins.
Millions of nephrons filter blood inside each kidney. In the two-part filtration system, each nephron contains a glomerulus and a tubule. Blood filters through the glomerulus and discharges through the tubule. The glomerulus allows blood and waste to pass through while preventing blood cells and larger molecules from passing through the membrane. Tubules subsequently receive the materials, sending the minerals back to the blood stream and urine to the bladder, reports Johns Hopkins.
Composed of extra fluid and waste from the filtration process, urine goes from the kidneys to the bladder through thin muscular tubes called ureters. As the bladder fills, the muscles in the bladder are relaxed. When the bladder is full, the brain receives a signal to urinate. Urine then passes through the urethra to the outside of the body, explains Johns Hopkins.