The millions of structures in the kidneys that filter toxins out of urine are called:

Nephrons

Nephrons are the basic structural and functional units of the kidneys. Each of the kidneys contains over a million nephrons. Nephrons function by filtering blood and then removing needed substances from the filtrate before eliminating the remaining fluid that contains water, metabolic waste, and toxins. as urine. This process occurs through three stages which are ultrafiltration, selective reabsorption and osmoregulation.