The skin, lungs, liver and large intestine in vertebrates are the accessory excretory organs.
1. Skin : Human skin possesses sweat glands and sebaceous glands. Sweat is an aqueous fluid containing sodium chloride, lactic acid, urea, amino acids and glucose. It serves mainly as a cooling process. Sweat contains 99.5% of water. The volume of sweat varies from negligible amount to 142 ml. a day depending upon activity and temperature. Sebum also contains excretory products like waxes, sterols and fatty acids. It also keeps skin oily.
2. Lungs : Lungs remove large volume of carbon dioxide produced in the body along with which some moisture is regularly excreted. Human living removes 182 ml. of C02/hr. and 400ml. of water per day in normal resting conditions volatile materials are also eliminated by lungs.
3. Liver : Liver is the principal organ for the excretion of cholesterol pigments (bilirubin and biliverdin) and inactivated products of steroids, hormones, some vitamins and many drugs.
