Role of other organs in excretion

The kidneys are the principal excretory organs, but they are not the only ones - several other organs quietly remove wastes of their own kind every day. The lungs remove large quantities of carbon dioxide (around 18 litres a day) along with significant amounts of water vapour with every breath. The liver secretes bile containing bilirubin and biliverdin (breakdown products of haemoglobin), along with cholesterol, steroid hormones and drugs, all of which leave the body mixed in with digestive wastes. The skin contributes through two types of glands: sweat glands, whose secretions mainly cool the body but also carry out small amounts of sodium, chloride, urea and lactate, and sebaceous glands, which release sterols, hydrocarbons and waxes a …