Zach: Plasma is the blood that goes to the kidneys. It produces 200 liters of filtrate, which looks like urine. He says it doesn't make it all the way to our urethra - so we don't pay out that much. Zach: We've got two million of them. So one million each kidney. I have no idea how long a nephron is. They vary in length depending on which nephrons,. Because some nephrons are shorter than others.