We have two kidneys, each about the size of your fist. Each kidney contains approximately 1 million microscopic filtering and processing units called nephrons. Each nephron contains a tiny filter called a “glomerulus” (glo-MER-yoo-lus). Glomeruli are microscopic balls of capillaries, or blood vessels, which filter the blood that passes through them. The kidneys clean and process the blood; working together, the 2 million nephrons filter and process 3-4 liters of blood approximately every 5 minutes, 24 hours a day, 7 days a week.