During matabolic activities the harmful waste products produced in the body are eliminated by the body. This is known as excretion. There are several organs such as skin, liver, lungs, large intestine and kidneys, etc. known as excretory organs of the body. These organs help in performing the osmoregulatory function of the body.
The animals are divided into three types on the basis of protein break down.
1. Ammonotelic Animals : Amonia is a toxic substance. Animals which eliminate amonia are known as ammonotelic animals. Ammonotelic animals are Protozoans, Sponges, Jelly fish, Fresh water fishes etc.
2. Ureotelic Animals : Animals which excrete uric acid are known as uricotelic animals. Uric acid is less toxic then ammonia and urea. Ureotellic animals are reptiles, birds, insects etc. Desert animals such as camels, kangaroos, rats, amphibians etc are also ureotellic animals.
3. Uricotelic Animals : Animals which excrete uric acid are known as uricotelic animals. Uric acid is less toxic then ammonia and urea. Uricotelic animals are reptiles, birds, insects etc. Desert animals also eliminate uric acid.
Excretory organs
(a) Skin of mammals : Mammals have sweat glands which give out the excess of salts as sweat. Water vapour and co2 is expelled out by lungs. Large intestine expells out faecal matter. Liver excretes hormones and some vitamins with bile.
2. Kidneys : Kidneys are well known organs of excretion. Liver, skin, lungs and intestine also help in excretion. In man there are two kidneys situated in the abdominal cavity on both sides of the vertebral column. They eliminate urine into renal pelivis. Kidneys are very important organs in man.
In humans urine is filtered at + 15 mm of Hg. Urine filtered in 24 hours = 1.5 litres.
Urine formation takes place in three steps namely ultra filteration, reabsorption and secretion.
Urine is composed of organic and inorgamic substances. In organic substances are urea, creatine, Ammonia, Hippuric acid, Amino acid, Uric acid, Oxalic acid, Vitamins, Hormones, Enzymes etc. Inorgamic substances are Nitrogen, Sodium, Calcium, Potasium, Iodine, Lead, Magnesium, Arsenic etc.
Urea Cycle : Ammonia is released in oxidative deamination in liver. This ammonia now undergoes ornithine-arginine cycle and gets converted into urea.
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