The kidneys sit at the back of the abdominal wall and at the start of the urinary system. These organs are constantly at work: Nephrons, tiny structures in the renal pyramids, filter gallons of blood each day. The kidneys reabsorb vital substances, remove unwanted ones, and return the filtered blood back to the body. As if they weren’t busy enough, the kidneys also create urine to remove all the waste.
1. The Kidneys Are Retroperitoneal Organs in the Abdomen
The kidneys are located behind the peritoneum, and so are called retroperitoneal organs. They sit in the back of the abdomen between the levels of the T12 and L03 vertebrae. The right kidney is slightly lower than the left kidney to accommodate the liver. Both kidneys are bean-shaped and about the size of an adult fist.
2. Blood Flows In and Out of the Kidneys Through Renal Arteries and Veins
Blood enters the kidneys through renal arteries. These arteries branch into tiny capillaries that interact with urinary structures inside the kidneys (namely the nephrons). Here the blood is filtered. Waste is removed and vital substances are reabsorbed back into the bloodstream. The filtered blood leaves through the renal veins. All the blood in the body moves in and out of the kidneys hundreds of times each day—that’s about 200 quarts of liquid to be filtered every 24 hours.