Blood is filtered through the glomerulus which acts like a sieve forming the filtrate or what remains. The filtrate is then processed by the nephron to reabsorb into the blood valuable materials the body can use. Other materials left in the nephron form waste materials. The filtering of water and various components in and out of the blood by the human kidney are dependent on varying pressures, permeability, and concentration gradients. The excretory system recycles and reabsorbs what the body can use and removes waste materials the body can't use as urine.