We will discuss here about the human excretory system of our body
In a living body two types of reactions always go on. These two are anabolism and catabolism. Anabolism means making new, things and catabolism means breaking down of any substance into simpler forms. The combination of both anabolic and catabolic reactions, which occur continuously in our body is called metabolism.
During metabolism some materials are produced within our body, which are harmful to us. These unwanted and harmful materials are called excretory materials and the process by which these materials are removed from our body is called excretion.
Certain organs play important role in excretion. These organs are known as excretory organs. The main excretory organ of human body is a pair of kidneys. Each kidney is a dark brown bean- shaped structure. It is located near the back wall of abdominal cavity at two sides of our backbone. The inner side of a kidney, that faces the backbone, is concave and its outer side is convex. In each kidney a thick blood vessel enters and another blood vessel goes out. The incoming blood vessel carries the blood full of excretory materials. The kidney filters the blood and separates those excretory materials from it. Now fresh blood flows out from it through the outgoing blood vessel.
Filtering of blood occurs within numerous very fine and minute tubules, present within the kidney, which are called nephrons.
With the help of these nephrons kidney separates out excretory materials, excess salts and water from blood. This mixture is called urine. It comes out from each kidney through a long tube, called urethra. Two urethras from two kidneys open into a muscular sac, situated in our lower abdominal cavity. This sac is called urinary bladder. A tube emerges from the urinary bladder, which is called urethra. When the bladder becomes full we feel a pressure and pass out urine through this urethra.