The differences between the vagina and the urethra are as follows: 1. In terms of function, the vagina is the female organ of intercourse and the channel for delivery of the fetus and menstruation, while the urethra is the channel for the discharge of urine. 2. In terms of subsystem, the vagina belongs to the reproductive system, while the urethra belongs to the urinary system. 3. The depth of the vagina is between about 7-12 cm and is tolerant of expansion, allowing it to expand with the invasion of foreign bodies. The urethra is about 2.5-5 cm long and is not expandable, so forcible invasion of foreign bodies can cause damage to the urethra. 5. The vagina is lubricated by exudate from the vaginal wall and fluid from the cervical mucus glands, which often results in a milky and egg-white discharge, while the urethra has no such discharge.