This is the flask-shaped tube that connects the introitus with the uterus. The cervix (neck of the uterus) protrudes into its upper end. Its wall is composed mainly of muscle, and it is lined with a strong, folded membrane richly supplied with blood vessels. The bladder and urethra (the tube through which urine passes from the bladder) lie in front of it, and the rectum (the lower end of the large bowel) lies behind. The vagina has some surprising features. First, there is its great ability to expand. Most of the time it is 9-12 cm long and its cavity is collapsed, with the front and back walls touching (like an empty bag). This cavity opens easily when anything goes into it, such as your fingers, a tampon, or a speculum. During sexual excitement the vagina becomes 5-7 cm longer and its cavity dilates in readiness to receive the penis. During childbirth it expands to a width of up to 12 cm to allow the baby to pass through. The elasticity of its strong, muscular wall and the folds in its lining allow the vagina to expand to this extent without tearing.
The lining consists of a surface layer many cells thick (stratified squamous) lying on a layer that carries its rich blood supply. Worn cells are constantly shed from its surface, and are replaced by new cells from the deeper layers. Its inner surface is kept moist though there are no glands in the vagina (the mouth, lined by a similar membrane, needs the secretions of salivary glands to remain moist). Fluid oozes into the vaginal cavity from blood vessels within the lining. During sexual arousal, when these blood vessels become engorged, the amount of fluid increases greatly to provide lubrication for intercourse.
The vaginal environment
The vagina isn’t a sterile place. Bacteria essential for vaginal health live in it, and bacteria that normally abound on the skin outside the introitus can easily enter and survive in the warm, damp vaginal space. Anything that goes into the vagina (fingers, tampons, a penis) will also carry in skin bacteria. We may have up to 30 different types of bacteria in our vaginas, but not necessarily doing any harm. These bacteria may not be natural inhabitants of the vagina, in that they prefer to live in other places (for example bowel bacteria), but they can live in the vagina without causing any problems unless they reach excessive numbers. Their numbers won’t rise to troublesome levels unless the vagina’s defences are broken down. The vagina’s acidity and its natural inhabitants – Doderlein’s bacilli – are its defences.
Vaginal acidity
The fluid in the vagina is quite acid. If you’ve studied chemistry or biology you’ll know that acidity and alkalinity are ex-pressed as pH. In health the vagina stays at around pH 4-4.5 (most other body fluids, such as blood, have a neutral pH of 7). Vaginal acidity is maintained by the action of Doderlein’s bacilli on a type of sugar – glycogen – that is produced, under the influence of oestrogen in the blood, in the cells near the surface of the vaginal lining. When these cells are shed, Doderlein’s bacilli feed on the glycogen, producing lactic acid in the process. The presence of lactic acid favours the growth of Doderlein’s bacilli but prevents other bacteria from flourishing. Thus vaginal acidity acts as a mild antiseptic to keep unwanted bacteria at harmless levels.
Sperm survive best in a slightly alkaline environment, so vaginal acidity is hostile to sperm. However, for an hour or two after ejaculation, sperm are protected because the acidity is neutralised by seminal fluid and cervical mucus (both alkaline) and the increased fluid (neutral, because it comes from blood) that oozes through the vaginal walls during sexual arousal.
The healthy vagina is good at keeping itself clean and free from infection. Its strong lining has no weak spots such as hair follicles and glands; bacteria can’t get in through an unbroken surface. Its acidity defends against unwelcome germs, which are carried away with any dead cells
The lining changes with the rise and fall of hormones during the menstrual cycle. When oestrogen is high, it becomes thicker, produces more glycogen and sheds more surface cells. Bacteria acting on the cells and glycogen produce volatile substances with an odour (pheromones) believed to be important in sexual attraction. These effects are reduced after ovulation when progesterone is high.
Surprisingly, the vaginal lining has no touch or heat sensation beyond 2 cm from the introitus. This is why you can’t feel a tampon that is in the right place (and not too far down). The sensation from a speculum in the deeper parts of the vagina is from movement and stretching of its walls.
If you’ve never felt inside your vagina, try it. If you feel uneasy about doing this, think about it being like feeling inside your mouth, a similar space connecting an important internal system with the outside. You don’t need to wear surgical gloves or sterilise your fingers, but wash your hands just as you would before putting your fingers in your mouth.
Your vagina will take up to three fingers easily. Inside, the lining feels wet and wrinkled (the folds in the lining). Beyond the first 2 cm, the cavity opens out and you can sweep your finger(s) around more widely. It also changes direction, taking a sharp turn towards your back. It’s important to remember this change of direction when inserting tampons.
Press your fingers along the front wall of your vagina. You will probably feel as if you want to pass urine as the pressure is transmitted through the thin layer of tissue that separates your vagina from your bladder and urethra. Insert your fingers to their full length and you’ll be able to feel your cervix. It’s a firm knob 2-4 cm across with a dimple in the middle. It feels rather like the tip of your nose, including that it has a bit of side-to-side and up-and-down movement.
What’s a normal vaginal discharge?
In health, the fluid that drains through the introitus consists of whatever drains from the uterus (not much, except during menstruation), some secretion from the cervix and the fluid that moistens the vagina. It is clear or white or pale yellow when it first appears, and has a characteristic sweetish smell that’s not noticed by others or you if normal hygiene is maintained. After it has dried on your underpants and become mixed with drops of urine and sweat, it can darken and smell less sweet, so daily washing and changing are important. The amount and feel of the discharge varies from woman to woman and from time to time, according to where you are in your menstrual cycle and whether or not you’ve been sexually excited. You’ll get to know your own variations and will easily recognise any abnormal change in the discharge.
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