This system is responsible for the waste and elimination of urine.

Aspects of this system include:

   -  Kidney
   -  Ureters
   -  Bladder
   -  Urethra

Humans produce around 1.5 liters of urine in a 24-hour period.

Kidney

The kidney concentrates the urine by regulating electrolytes and remove
urea from the blood and other wastes. 

Urea is an organic compound that was discovered in 1773
This compound is soluble in water and is essentially a waste product
Production of urea occurs in the liver and is the result of the breakdown of some amino acids.

Bladder

The bladder is an organ that is hallow.  It is layered similar to a balloon
with several muscles that make up this organ. The muscle is a smooth muscle

This allows the bladder to enlarge when it becomes full and small when empty.
Overall the bladder can hold 400-620 ml but the maximum is twice this amount if
outflow is obstructed.

Females:  The bladder lies just behind the uterus and near the vagina. 

Urethra

This is the endpoint of the urinary system.  Urine and other wastes start
from kidney and then to the bladder prior to pasing through the urethra and then
out though the vaginal opening

This tube connects the bladder to the outside of the body.
Control of excretion of urine is through the urethral sphincter