What Is the Main Function of the Excretory System?

Purestock/Getty Images

The excretory system is a collection of organs tasked with removing excess nitrogen and other toxins from the body. The kidneys, liver and large intestine perform most of the filtration duties. Solid waste passes out through the colon, gaseous waste exits the body through the lungs and excess liquid leaves through the bladder and skin.

The excretory process begins when the liver creates bile, passing it into the gallbladder and on to the lower intestine. Bile begins to break down solid wastes and is capable of transforming substances, like ammonia, into less harmful urea. Bile also serves an important role in breaking down lipids, separating useful fats from waste products. Urea, salts, and nitrogen byproducts are absorbed into the bloodstream. Here they pass through to the kidneys and are filtered out into the bladder. Excess water may also be routed to the skin. There, it flows through sweat glands and evaporates, taking salts and other contaminants with it.

The remaining solid matter passes through the small intestine into the large intestine, where any remaining water is removed and circulated through to the bladder. The remaining solid waste is converted into fecal matter and passes out of the body through the colon.