Is Sexual Intercourse Painful for You? The vagina is the muscular tube which provides the passageway from the outside of the body to the uterus womb. This can cause the uterus to rise into the pelvis and create what is called the "ballooning effect" in which the vaginal walls stretch and contract around the penis to provide stimulation and encourage ejaculation. During childbirth, the vagina provides the passageway through which the baby is delivered. When the cervical dilation is larger than four inches 10 centimeters , the baby will pass from the uterus into the vagina. As the far end of the vaginal passage, the ectocervix the external portion of the cervix bulges prominently into the vaginal canal. Functions of the Cervix in Reproductive Health. The vagina is composed of tissues, fibers, muscles, and nerves. The length of the vagina can vary in women of child-bearing age from between 2.