There are 2 kidneys in human body. Each weighs about 125 gms. These are located one on each side of the spine in abdomen. These are covered and protected in their upper part by ribs. These are bean shaped and beans are said to be kidney shaped.
Each kidney has about 1 million filtering units. These are called renal corpuscles and can be seen by microscope . The ball like portion where formation of urine begins by filtering from blood is called glomerulus. The filtered fluid gets modified while passing through tube like structures.
Kidneys are very rich in blood supply. It gets more blood per 100 gms of tissue than any other organ except heart. About one fifth of the total blood pumped by heart goes to the kidneys.
After the urine is formed in the kidneys, it comes to the urinary bladder by two tubes called ureters. The urine can be stored in bladder till voided at will. Various valve like structures prevent urine from flowing backwards and leakage through the urethra , the final part connecting bladder to the outside.