The Role of the Vagina in Sex and Reproduction

Understanding Its Function From Arousal to Childbrith

The human female external genitalia.
Getty Images/Encyclopaedia Britannica/UIG

The vagina is the muscular tube which provides the passageway from the outside of the body to the uterus (womb). The vagina has the ability to change in size to accommodate sexual intercourse and provide the "birth canal" through which a baby can be delivered.

Structure of the Vagina

The vagina is composed of tissues, fibers, muscles, and nerves. The outermost mucosal tissue is underpinned by a layer of connective tissue which work together to produce mucus for vaginal lubrication.

Beneath these is a layer of smooth muscle, which can contract and expand, followed by another layer of connective tissue known the adventitia.

The vagina is positioned between the vulva (the external genitalia) and the cervix (the narrow, neck-like passage which separates the vagina from the uterus).

The general structure of the vagina is as follows:

  • The opening of the vagina lies between the anus and the opening of the urethra (through which urine exits the body). The vaginal and urethral openings are protected by the labia.
  • Right below the urethra lies the introitus, also referred to as the vestibule or the opening to the vagina.
  • The vaginal canal then travels upward and backward, between the urethra at the front and the rectum at the back.
  • As the far end of the vaginal passage, the ectocervix (the external portion of the cervix) bulges prominently into the vaginal canal.

The length of the vagina can vary in women of child-bearing age from between 2.5 inches to 3.5 inches on average.

In terms of lubrication, vaginal secretions can increase during sexual arousal, pregnancy, and different stages of menstruation. During the menstrual cycle, the mucous membrane will thicken and the composition of the mucus will change to better facilitate fertilization.

The Vagina and Sexual Intercourse

During sexual arousal, the mucosal membranes of the vagina will begin to produce more lubrication as the vagina expands both in length and width.

This reduces the friction and risk of injury during vaginal penetration.

The vagina can continue to lengthen as a woman become fully aroused as the cervix takes the opposite tack and begins to retract. 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.

The vagina itself does not have many nerve endings which is why many women are unable to achieve sexual stimulation from vaginal penetration alone. On the other hand, the clitoris is rich in nerves and can work in tandem with the vagina to achieve orgasm during sexual intercourse.

The Vagina in Childbirth

During childbirth, the vagina provides the passageway through which the baby is delivered. When labor begins, a woman with typically experience vaginal discharge, labor contractions, the rupture of membranes, and either the gush or stream of amniotic fluid from the vagina.

As delivery approaches, the cervix will begin to thin and soften, allowing the baby to drop into the pelvis. The baby will then begin to lose the support of the cervix as contractions start and the cervical os (opening) begins to dilate.

When the cervical dilation is larger than four inches (10 centimeters), the baby will pass from the uterus into the vagina. The structure of the vagina is such that it is able to stretch to many times its normal diameter to accommodate delivery.

Following pregnancy and the return of the normal estrogen flow, the vagina will return to its approximate pre-pregnancy state in around six to eight weeks.


Schuiling, K. and Likis, F. (2016) Women's Gynecological Health (Third Ed.) Burlington, Massachusetts: Jones and Bartlett Learning. ISBN-13: 978-1284076028.