Describe the role of liver, lungs and skin in excretion.
Other than the kidneys, lungs, liver and skin also play important roles in the elimination of excretory wastes from the human body.
The lungs remove large amounts of carbon dioxide, approximately 200mL per minute, along with significant quantities of water every day. This gaseous elimination is a vital excretory function.
The liver, being the largest gland in our body, secretes bile containing various excretory substances. These include bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins and drugs. Most of these substances ultimately pass out of the body along with digestive wastes.
The skin helps in excretion through two types of glands. The sweat glands produce a watery fluid containing NaCl, small amounts of urea, lactic acid, etc. Though the primary function of sweat is to provide a cooling effect on the body surface, it also helps in the removal of some wastes.
The sebaceous glands eliminate substances like sterols, hydrocarbons and waxes through sebum, which provides a protective oily covering for the skin. Additionally, small amounts of nitrogenous wastes can also be eliminated through saliva.
Explanation
This answer covers all three organs mentioned in the question (liver, lungs, skin) with specific details from NCERT textbook Section 16.7. The lungs' role in CO₂ and water removal, liver's role in bile secretion with specific waste products, and skin's dual glandular mechanism (sweat and sebaceous) are all explained. The answer follows the 5-mark format with 5 paragraphs and uses bold for key terms as per exam requirements.