The process that involves the expelling of urine from the urinary bladder is
Micturition
Micturition is the process in which urine is expelled from the urinary bladder through the urethra by relaxation of the sphincter muscles, located at the opening of the urinary bladder, into urethra under impulse from the nervous system. Excretion is a broader term for the process of elimination or expulsion of waste matter from the body. Parturition is the action of giving birth to young ones. Egestion is the discharge or expulsion of undigested material (food) from a cell in case of unicellular organisms, and from the digestive tract via the anus in case of multicellular organisms.