The vagina is a part of the female reproductive system. It is a muscular canal that connects the uterus to the exterior of the body. During the birthing process it is also referred to as the birth canal.
The exterior opening of the vagina is protected by the labia (lips) and vulva, while the cervix of the uterus extends into the vagina, forming the interior end of the vagina.
A vagina has three functions. In sexual intercourse, the vagina accommodates the penis. A vagina has a certain amount of elasticity that allows this to occur. This elasticity also aids in the birthing process, expanding so the baby can pass through. Not only does the vagina serve as the birth canal, but it is also the passageway for a woman's menstrual flow from the uterus.
The vagina can be from seven to nine centimeters long and can expand in both length and width. It has a soft protective lining packed with nerve endings, especially at the entrance. This relays pleasurable sensation during sexual activities for most women.