Describe the role ofliver, lungs and skin in excretion.

Liver,lungs, and skin also play an important role in the process ofexcretion.

Role ofthe liver:

Liver isthe largest gland in vertebrates. It helps in the excretion ofcholesterol, steroid hormones, vitamins, drugs, and other wastematerials through bile. Urea is formed in the liver by the ornithinecycle. Ammonia – a toxic substance – is quickly changedinto urea in the liver and thence eliminated from the body. Liveralso changes the decomposed haemoglobin pigment into bile pigmentscalled bilirubin and biliverdin.

Role ofthe lungs:

Lungs helpin the removing waste materials such as carbon dioxide from the body.

Role ofthe skin:

Skin hasmany glands which help in excreting waste products through pores. Ithas two types of glands – sweat and sebaceous glands.

Sweatglands are highly vascular and tubular glands that separate the wasteproducts from the blood and excrete them in the form of sweat. Sweatexcretes excess salt and water from the body.

Sebaceousglands are branched glands that secrete an oily secretion calledsebum.