Question

Describe the role of liver, lungs and skin in excretion.

Answer 1

Excretion is the process of removal of metabolic waste products from body. In vertebrates, it is done by liver, lungs and skin. All these organs together form the excretory system.

Complete answer:
1: Role of Liver- Liver is the largest gland in the human body. It purifies the blood and helps in excretion of steroid hormones, drugs, cholesterol, vitamins and other waste materials, through bile. Highly toxic ammonia is converted to urea (in Urea cycle or ornithine cycle), in the liver for excretion. Liver also converts hemoglobin pigments into bile pigments (bilirubin and biliverdin) for excretion.
2: Role of Lungs- In the respiratory system, lungs excrete waste products (carbon dioxide and water). Lungs eliminate these unwanted, waste products from the body, through expiration (exhaling air out from the body).
3: Role of skin- In mammals, the skin does the excretion using the sweat glands, or oil glands, or sudoriferous / sebaceous glands present in them. The sweat glands secrete waste fluid in the form of sweat (perspiration). The sebaceous/oil glands secrete sebum, which contains lipids like waxes, sterols other waste compounds. In this way the fluid waste is eliminated out of the body through skin.

Note:
Liver is the main site for excretion of inactive.
The large intestine also plays an important role in excretion by eliminating Ca2+, Mg2+, and Fe2+ in the lumen, which is further excreted via faecal matter.