What do the kidneys do?

At the back of the belly, one on each side of the spine, roughly at waist level and protected by the lower ribs.

Yes. One healthy kidney can do the work of two, and many people live normally with just one. That is why a living person can donate a kidney.

Blood passes through millions of tiny filters in the kidneys. They separate out water and what the body doesn’t need, return what is still useful to the blood, and the rest becomes urine, which flows down the ureters to the bladder.

In an adult, 300 to 500 ml comfortably. The urge to go appears before the bladder is completely full. In children, the capacity is much smaller.

Small stones that form when substances in urine clump together and harden. Small ones can pass on their own; when they move through the ureter they usually cause sharp pain in the back. Drinking water helps prevent them.

The kidneys, ureters and bladder work the same way. The biggest difference is the urethra: about 4 cm long in women and about 20 cm in men. Because it is shorter, women get urinary infections more often. In women, the uterus sits right behind the bladder.