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how does nephron filitrate blood
The actual removal of wastes occurs in tiny units inside the kidneys called Nephrons. Each 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. The Glomerulus acts as a filtering unit, or sieve, and keeps normal proteins and cells in the bloodstream, allowing extra fluid and wastes to pass through. A complicated chemical exchange takes place, as waste materials and water leave the blood and enter the urinary system.At first, the tubules receive a combination of waste materials and chemicals the body can still use. The kidneys measure out chemicals like sodium, phosphorus, and potassium and release them back to the blood to return to the body. In this way, the kidneys regulate the body's level of these substances. The right balance is necessary for life.

In addition to removing wastes, the kidneys release three important hormones:

    Erythropoietin, or EPO, which stimulates the bone marrow to make red blood cells
    Renin, which regulates blood pressure
    Calcitriol, the active form of vitamin D, which helps maintain calcium for bones and for normal chemical balance in the body.


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