filtering occurs in tiny units inside your kidneys called
nephrons. Every kidney has about a million nephrons. In
the nephron, a glomerulus—which is a tiny blood vessel,
or capillary—intertwines with a tiny urine-collecting
tube called a tubule. A complicated chemical exchange
takes place, as waste materials and water leave your blood
and enter your urinary system.
the tubules receive a combination of waste materials and
chemicals that your body can still use. Your kidneys
measure out chemicals like sodium, phosphorus, and
potassium and release them back to the blood to return to
the body. In this way, your kidneys regulate the body’s
level of these substances. The right balance is necessary
for life, but excess levels can be harmful.