kidney

·       The kidney

·       The two bean-shaped kidneys are situated one on either side of the vertebral column, on the posterior side of abdomen.

·       The functional unit of the kidney that performs the basic function of filtration is called a nephron.

·        Each nephron has a cup-like, thin-walled upper part called the Bowman’s capsule.

·       The network of capillaries in it is called a glomerulus.

·       The urea produced in the liver comes into the blood.

·        When the urea-containing blood comes into the glomerulus, it is filtered through its capillaries and urea and other similar substances are separated from it.

·        Water molecules and small molecules of some other substances can cross the semipermeable membrane of Bowman’s capsule.

·       The solution accumulated in the cavity of Bowman’s capsule passes into the tubular part of the nephron.

·       Here, molecules of water and some other useful substances are reabsorbed into the blood. Urine is formed from the remaining solution which is full of waste materials.

·       The urine is carried by the ureters and stored in the urinary bladder.

·       Afterwards, urine is given out through the urethra. The urinary bladder is muscular and it is under the control of nerves.

·        Hence, we are able to keep a control on urination.

 Though the kidneys are the main organs of excretion in human beings, the skin and lungs also help in the process of excretion