11th Class Biology Excretory Products and their Elimination Accessory Excretory Organs

(1) Skin : Many aquatic animals, such as Hydra and starfish, excrete ammonia into the surrounding water by diffusion through the body wall. In land animals, the skin is often not permeable to water. This is an adaptation to prevent loss of body's water. Mammalian skin retains a minor excretory role by way of its sudoriferous, or sweat glands and sebaceous, or oil glands.

(i) Sweat gland : Sweat glands pass out sweat. The latter consists of water containing some inorganic salts (chiefly sodium chloride) and traces of urea and lactic acid. It also contains very small amounts of amino acids and glucose.

(ii) Sebaceous glands : Oil glands pass out sebum that contains some lipids such as waxes, sterols, other hydrocarbons and fatty acids. 

(2) Lungs : Carbon dioxide and water are the waste products formed in respiration. Lungs remove the\[C{{O}_{2}}\]and some water as vapour in the expired air. Lungs have access to abundant oxygen and oxidise foreign substances, thus causing detoxification and also regulate temperature.

(3) Liver : Liver changes the decomposed haemoglobin of the worn-out red blood corpuscles into bile pigments, namely, bilirubin and biliverdin. These pigments pass into the alimentary canal with the bile for elimination in the faeces. The liver also excretes cholesterol, steroid hormones, certain vitamins and drugs via bile.

(4) Large intestine : Epithelial cells of the colon transfer some inorganic ions, such as calcium, magnesium and iron, from the blood into the cavity of the colon for removal with the faeces.

(5) Saliva : Heavy metals and drugs are excreted in the saliva.

(6) Gills : Gills remove \[C{{O}_{2}}\] in aquatic animals. They also excrete salt in many bony fish.