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of the Vagina
Jump to Anatomy of Vagina
Jump to Nerves of Vagina and Pelvis
Jump to Blood Supply of Vagina
Jump to Developmental Anomalies
Jump to The Protective Vaginal Environment
Jump to Vaginal and Vulvar Fluids
Jump to Normal Vaginal and Vulvar Fluids (Photographs)
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Go to How to Sexually Stimulate
the Vagina
The following illustration reveals the deep pelvic muscles, but also incorrectly shows the vagina as an open cavity within the body, partly as a result of being based on human dissections.(3) During life, the pelvic muscles are always under a slight amount of tension, which is necessary to hold the contents of the pelvis in place, as otherwise they would be forced out by gravity. This normal tension, called resting or basal tone, holds the vagina closed except when something is inserted. If these muscles are too tight, inserting objects into the vagina may be painful or impossible. If they are injured or weak, then incontinence or prolapse (photographs of prolapse) are a possibility. This is why it is very important for the pelvic muscles to be strong yet flexible. Contrary to common folklore, a tight vagina, requiring the presence of tense pelvic muscles, isn't normal or healthy.
The following illustrations reveal the typical placement and alignment of the vagina and uterus within the body, and what happens to their alignment when the pelvic muscles become weak; the pelvic muscles have been highlighted in red.(3) Also note how the vagina normally doesn't follow a straight line into the body, which is something important to be aware of when inserting rigid objects. MRI images shown farther down on the page also reveal this internal alignment. In 20% of women the uterus is normally tilted to the rear rather than the front or straight up, which you can learn more about here and here.
Beyond the pelvic muscles, the vagina, uterus, and other pelvic organs are held in place by several supporting structures. These features are commonly left out of anatomy illustrations for reasons of visual clarity, but give the false impression the organs simply float within the pelvis. The following illustration provides an indication of how complex and extensive these supporting structures are. The orientation of this illustration may be a bit confusing: picture a woman standing, the vulva is at the bottom, the tail bone is to the left, and the pubic bone is to the right. While the presented shape of the vagina, at three different locations, aren't completely accurate, they do demonstrate how the supporting structures influence the shape of the vagina at these locations.
Inside the pelvic cavity, the vagina merges with the cervix. Since the cervix is made up of a different type of tissue than the uterus it is considered an entirely separate organ.[1] In a way, the cervix forms the external orifice for some of the internal female reproductive organs (the uterus, fallopian tubes, and ovaries). The cervix must act as a barrier to the outside world because objects and microscopic organisms can enter into the vagina relatively easily, which would place the uterus and a developing fetus at risk of infection if it did not. This is also why the vagina has an elaborate system of defenses that help protect against unwanted invasions, while still allowing one extremely important invasion; more on that later. It is the cervix that must create a physical barrier that will keep harmful organisms out of the internal pelvic organs, or a pelvic infection (PID) is a possibility. Menstruation serves to help protect the uterus and internal reproductive organs from infection by periodically shedding its lining, because if sperm can at times enter the uterus through the cervix so might other organisms.(1)
The vagina increases in size a bit at its junction with the cervix, but is still a collapsed potential space. The cervix projects down into the vagina; envision a tennis ball inserted into a sock. The area between the cervix and vaginal wall is called a fornix. There are the anterior (front), posterior (back), and lateral (side) fornices, with the posterior fornix being the largest potential space. The following illustration shows the anterior and posterior fornices, and demonstrates how this causes the front wall of the vagina to be slightly shorter than the rear wall, by about 1/2 inch (1.23 cm) on average.[2]
When not sexually aroused, the front wall of the vagina is about 3 inches (7.6 cm) on average in length, with a range of 2.3 to 3.7 inches (5.8 to 9.3 cm), and the rear wall is about 3.5 inches (8.8 cm) in length on average, with a range of 2.8 to 4.2 inches (7.1 to 10.6 cm). The width of the vagina is 1.4 inches (3.4 cm) on average, with a range of 0.8 to 2.0 inches (2.1 to 5.0 cm).[2] This length does not take into account the depth of the vulva, which is the distance between the outer labia and vaginal orifice, commonly called the introitus or vestibule, and depicted in the illustrations shown above. The depth of the introitus is about 1 inch (2.6 cm) on average, ranging from 5/8 to 1 3/4 inches (1.5 to 4.6 cm).[3]
This means on average, the vulva and vagina can receive objects 4 to 4.5 inches in length, depending on whether the object enters the anterior or posterior vaginal fornix. It also means the average penis, having a length of 5.1 to 5.9 inches (12.9 to 14.9 cm), is sufficiently long to fill the length of the vagina.[4] During sexual arousal, the vagina is reported to lengthen by up to about 50%(2), resulting in a length of perhaps 4 1/2 inches (11.4 cm). This last observation is debatable, as a study performed in 1991 using MRI found only the front wall of the vagina increased in length, and then only by 1 cm (0.4 inches). The uterus' position "hardly changed." indicating it is unlikely the vagina increases much in length during sexual arousal.[5] The vagina may stretch under pressure, when an object is inserted, but it doesn't appear to do much of this on its own.
The following MRI images demonstrate the potential space created by the vaginal fornices. The first image shows the normal resting position of the vagina, cervix, uterus, and bladder. In the second image, a liquid gel has been injected into the vagina to aid in creating a medical diagnosis, but in the process demonstrates the shape and elasticity of the upper vagina and the area surrounding the cervix. This is important to note, as it helps illustrate where a tampon or a penis should be positioned if they are to fit comfortably and fully within the vagina. If objects are angled incorrectly when inserted they may hit against the cervix rather then entering into the vagina fully.
In the following MRI images observe how large the bladder, highlighted in blue, has become in the image on the right, and how this has altered the position of the uterus and vagina. This change in size is the result of increased urine being stored within the bladder, as the bladder is much like a balloon that requires internal outward pressure for it to expand. This pressure and resulting movement of the internal organs may in part explain why a full bladder alters a woman's sexual experiences, and may even trigger physical sexual arousal. (The original reference does not comment on the significance of the increased size of the bladder.)
The following images reveal the position of the erect penis during vaginal intercourse, when couples are in the missionary position. The tip of the penis is positioned in the posterior fornix. Some women find it pleasurable when the penis and other objects press or bump into the cervix during sexual activities, others find it uncomfortable or painful. The cause of these different experiences is unknown, but one potential cause of pain is endometriosis.
The following photographs reveal what the inside of the vagina looks like when viewed through a speculum. As you can see, there are many bumps and ridges, which are called rugae. This irregular surface may cause concern when women explore their vagina for the first time, as the vagina is often portrayed as a perfectly smooth tube. From the time a girl is a few week old infant until she experiences the onset of puberty her vagina looks and functions much differently than shown here. (4)
The following photograph reveals what the vaginal wall looks like when viewed straight on, which isn't normally possible. This accordion like appearance is the result of the vagina's ability to stretch sufficiently to allow an erect penis or full term infant to enter.
The wall of the vagina is comprised of three layers of tissue:
The inner most mucosal or mucus layer is made up of the same tissue as the inside of your mouth, nonkeratinized stratified squamous epithelium. These skin cells are sensitive to the hormonal changes of the menstrual cycle, namely the hormone estrogen.[6] Despite being a mucus membrane there are no glands inside the vagina that produce mucus secretions. Normal vaginal moisture "percolates" through the epithelium from the abundant blood vessels present in the underlying tissue (lamina propria). During the reproductive years, the normal vaginal environment is "just moist" rather than producing a steady volume of fluid. There is a slight amount of fluid that seeps from the vagina in varying amounts throughout the menstrual cycle; this topic is addressed in the article about hygiene.[6] The vagina also reabsorbs some of the moisture present.[6] The normal or basal level of moisture present in the vagina isn't commonly sufficient to facilitate sexual intercourse. During sexual arousal, transudate and cervical mucus form tiny "bead-like droplets" that slowly, or not so slowly, pool together coating the vaginal canal, and most often the vestibule and beyond.[6] "The smooth, slippery quality of the formed fluid is probably due to its pick up of sialoproteins coating the vaginal epithelium from the cervical secretion."[6]
The middle, muscular or muscularis layer, of the vagina is comprised of two separate layers of smooth muscle, an outer longitudinal (lengthwise) and an inner circular (donut shaped) layer. Women don't have voluntary control over these muscles. They are normally under a small amount of tension, and active throughout the menstrual cycle, but especially during the onset of menstruation, though women generally aren't aware of this, except when it becomes painful (dysmenorrheic pain).[6] At this time, I don't believe we know how these involuntary muscles function during intercourse and other sexual activities. Involuntary contraction of these muscles may cause pain and prevent vaginal penetration, resulting in a condition called vaginismus.
The outer elastic layer of the vagina provides structural support.[6]
The following photograph illustrates how the female prostate gland, commonly called the G-Spot, may project into the vaginal canal; this may not be a "typical" example. It isn't unusual for there to be a raised ridge or area of firmness along the front or top wall of the vagina that may produce pleasure and female ejaculation when stimulated during sexual activity. This feature is more pronounced in some women than others. It is possible for this swelling to be indicative of infection, if associated with additional signs of infection. In this example, you can see evidence of the underlying individual ducts that make up the prostate gland, though they empty into the urethra and possibly the vulva rather than the vagina.
The following illustration demonstrates how the urethra may project noticeably into the vaginal canal. It isn't known if this illustration is based on an actual woman, or meant to graphically illustrate how the urethra lies within the vaginal wall of all women, even though the two organs are usually shown as completely separate and isolated.(5) This illustration could show what the inside of the vagina looked like in the example discussed and illustrated above, where the urethral orifice appears to be within the vaginal orifice. Stimulation of the top or front wall of the vagina will most likely stimulate the female urethra and prostate gland, and this is likely why the majority of women have said vaginal stimulation results in an urge or desire to urinate, at varying degrees of frequency and intensity during their sexual activities.
The following illustration gives you an idea of how much the vulva and vagina can dilate to allow the passage of an infant during childbirth. The black outline indicates the location of the pelvic bones that form the birth canal. If the birth canal is found to be too small for vaginal delivery, necessitating a Caesarian section, it is because the pelvic bones are positioned too close together for the size of the baby's head, not because the vagina is too small.[1] This illustration, and one shown above, allow us to see how the vagina must stretch in the direction of the anus when objects are inserted, or pass through it. Stretching or pressing the vagina in the direction of the pubic bones is likely to crush the urethra, prostate gland, and other soft tissues in the area, causing pain and possible injury.
