How do Kidneys Work?
Inside each kidney there are more than one million tiny units called nephrons. Each nephron is made up of a very small filter called a glomerulus, which is attached to a tubule. Water and waste products are separated from the blood by the filters and flow into the tubules. Much of this water is reabsorbed by the tubules and the wastes are concentrated into urine.
What Kidneys Look Like
An enlarged view of a nephron
The urine is collected from the tubules in a funnel-like renal pelvis and then flows through a tube called the ureter into the bladder. The bladder stores urine until you urinate. Urine passes out of the body through a tube called the urethra. The kidney normally makes one to two litres of urine every day depending on how much you drink.
The normal kidney has the ability to greatly increase its workload. If one kidney is lost, the other kidney can enlarge and do the work of two.