The human excretory system comprises of a pair of kidneys, a pair of ureters, a urinary bladder and urethra. Kidneys are bean shaped organs located on either side of the vertebral column in the lower abdominal cavity. On the concave median margin of each kidney there is a notch called hilum which leads into funnel shaped space called renal pelvis.
The renal pelvis is surrounded by an outer layer of tissue called renal cortex and an inner layer of tissue called the renal medulla. Kidneys filter metabolic wastes from the blood and excrete them as a liquid called urine. As kidneys form the urine, they also maintain the normal composition of blood, fluid and salt balance throughout the body tissues.
Urine formed in the kidney is brought to the urinary bladder by two hollow muscular tubes called ureters. Urethra is the small tube that leads urine to the outside of the body. From urinary bladder urine is passed outside via urethra during urination voiding of urinary bladder is called micturition.