Apart from kidney, liver, lungs, and skin also play important roles in the process of excretion.
1. LIver- The liver is the largest gland in vertebrates which helps in the excretion of compounds like cholesterol, steroid hormones, vitamins, drugs, and other waste materials via the production of bile. Urea is formed in the liver by the ornithine cycle whereas ammonia which is a toxic substance is quickly changed into urea in the liver and hence gets eliminated from the body. The liver is also responsible for changing the decomposed haemoglobin pigment into bile pigments in the form of bilirubin and biliverdin.
2. Lungs: The lungs help in removal of waste materials such as carbon dioxide from the body.
3. Skin: Skin possesses many glands that help in excreting waste products through pores in the skin. The two types of glands present in the skin are sweat and sebaceous glands. The sweat glands are highly vascular and tubular glands which separate the waste products from the blood and excrete them in the form of sweat. Sweat also removes excess salt and water from the body. Sebaceous glands are branched glands that secrete an oily secretion called sebum.