Waste products are removed from the blood in the kidneys through a process called filtration. Renal arteries deliver blood to microscopic structures called nephrons within the kidneys. In the nephrons, blood pressure forces plasma through specialized capillaries, called glomeruli, into the renal tubules. This filtrate contains waste products such as urea, creatinine, and excess ions. Subsequent processes, including reabsorption and secretion, occur in the renal tubules, allowing essential substances to be reabsorbed into the blood, while waste products are concentrated into urine. The formed urine then flows through the collecting ducts and is eventually excreted from the body.