The function of the excretory system is to remove waste and harmful by-products of normal metabolic processes from the body. If these waste products accumulate, they interfere with the delicate balance of oxygen, water, and nutrients needed for normal cell development. The main by-product of cell metabolism, carbon dioxide, is expelled by respiration, but cellular metabolism also produces a host of salts, fats, and excess chemicals, including carbon, hydrogen, oxygen, and nitrogen. The excretory system filters out those that are harmful and eliminates them so the body can maintain a state of homeostasis.