The function of the kidneys is to filter waste products from the bloodstream and recycle nutrients and ions. Additionally, kidneys play a significant role in regulating blood pressure, electrolyte balance, and red blood cell production.

The kidney structure is complex, multilayered and the functional unit for fine-tuned filtration is called a nephron.

In short, oxygenated blood enters the kidney through the renal artery. In the kidney, the blood is passed through nephrons, where waste product and excess water are filtered out from the bloodstream and directed toward the ureter and ultimately the bladder.

This way, the kidney processes up to 180 liters a day in humans, the vast majority of the filtrate being reabsorbed in the bloodstream resulting in a typical urine volume of only 3-5 three to five liters a day on average.

A diagram of the kidney and its blood supply. The kidney is a bean-shaped organ that filters waste products from the blood. The renal artery brings clean blood to the kidney, and the renal vein carries blood with waste products away from the kidney. The ureter is a tube that carries urine from the kidney to the bladder. The nephron is the basic functional unit of the kidney. It is made up of a glomerulus and a tubule. The glomerulus is a cluster of capillaries that filters blood. The tubule reabsorbs water and nutrients from the filtrate and produces urine.

Figure 1. Internal Structure of a Kidney