Role of skin in excretion
Skin of many animals is thin and permeable. It helps in diffusion of ammonia. Human skin is thick, impermeable and acts as accessory excretory organ. It shows presence of two types of skin glands - sweat glands and sebaceous glands.
Sweat gland - these are distributed evenly over the body surface. They are abundant on palm and facial part. These are simple unbranched tubular glands. The sweat is aqueous fluid containing glucose, NaCl, water, urea and lactic acid. It also helps in thermoregulation.
Sebaceous glands - they secrete oily substance called sebum. It mixes with the sweat on the surface of the skin making the skin softer and lubricating the hair. It protects from any injury and infection.
Role of lungs in excretion
Lungs are the respiratory organs of the body. They play an important role in excretion of volatile substances like CO2 and water vapour during respiration. CO2 and water are produced during the process of oxidation of glucose. Most of the water is used for metabolic processes and excess is thrown out in the form of water vapour and CO2 is removed along with expired air.