Excretary System in Animals Part II

Elimination of nitrogenous wastes is called as Excretion. Various types of excretory organs are present in different animals. While simple excretory organs are present in lower animals and invertebrates, very complex organs like mesonephric and metanephric kidneys are present in Chordates. In mammals Kidneys are the chief excretory organs. They not only eliminate nitrogenous wastes but also maintain fluid and solute balance in the body, hence establishing a balanced internal state, otherwise called as 'Homeostasis'.
Physiology of excretion can be understood with the help of mechanism of urine formation. This process can be divided into 3 processes - Ultrafiltration, Selective reabsorption and Tubular secretion. Due to the result of these three processes a concentrated urine is produced which ultimately is eliminated outside through urinary bladder.