Female Reproductive System

When discussing fertility it is important for men to have a working understanding of to understand the organs of the internal female reproductive tract and their functions.

  • Vagina – The vagina itself is an elastic tube-like structure that extends from the female external genitals up to the uterus.  The vaginal opening is a 1½ -2 inch (4-5cm) slit in the vestibule (similar in width to the erect penis).  The vagina itself is typically 3 to 3 ½ inches (7.5-9cm) long, but this is variable.  So for men who are worried about not being big enough – they will be since 99.99% of men have an erect penis longer than 3 ½ inches (9cm)[i].  In addition, most women feel intercourse at the entrance to the vagina, not deep inside the vagina, so how far the penis is inserted is something the man feels, not her.  Hearing this, many men may wonder if they’ll “run out of room” if the vagina is less than 4 inches (10cm) long since 95% of men have an erect penis longer than this.  During sexual arousal and intercourse the uterus can lift, thus increasing the length of the vagina.  The length of an erect penis and the vagina are nearly always compatible – even in men who are “above average” in size.  Remember, the vagina is also the birth canal and can stretch to sizes much larger than a penis.  So men typically don’t have to worry about “running out of room” or “inserting too far”.  However, the first time a woman has intercourse (or the first time in a few weeks) may require her vagina to “stretch”, so inserting/penetrating gently may prevent discomfort until the vaginal tissue is more flexible.  Some women are able to tell their their partner (or be told by her physician in pre-marital exam) if there are any concerns with the length or tightness of her vagina that may require some consideration on your part.  In fact, some women are given certain vaginal stretching exercises prior to marriage if they haven’t been sexually active.

    • Hymen – The lower portion of the vagina is separated from the vestibule by a flap of membrane known as the hymen.  In early puberty the hymen can partially or completely block the opening to the vagina.  The hymen often goes away due to use of tampons or after a woman becomes sexual activity.  It is important for women to ask their provider prior to becoming sexually active if her hymen is still intact as the first sexual penetration by the penis may cause the hymen to tear.  If the hymen is still there (even partially) it is often best to have the hymen removed during her pre-marital exam to eliminate the fear of tearing on the first sexual encounter. 


[i] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3890219/ (11/5/18)

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  • Cervix – At the top of the vagina is the cervix.  The cervix is a thick, circular muscle that forms the lower portion of the uterus and it protrudes down into the vagina.  The “os” is muscular hole in the cervix that creates the pathway for sperm to swim up into the uterus and allows the baby to pass from the uterus into the vagina/birth canal.  This os is filled with mucus which the sperm must swim through – this mucus also protects the sperm from the acid in the vagina.  Depending on a woman’s hormones at the time, the mucus can become thick making it difficult for sperm to swim through (birth control pills and pregnancy can thicken this mucus to prevent sperm from getting to an egg).  Around the time of ovulation this mucus thins out to allow sperm to pass more readily.

  • Fornix – Surrounding the cervix is a higher ringed area called the fornix.  During sexual intercourse, the glans of the penis can enter the fornix area for more “room”.  This typically isn’t felt by the man to be any different from the rest of the vaginal area. 

  • Glands - The vagina has glands that secrete fluids to keep the vaginal tract moist and to reduce penile friction during intercourse.  These glands develop from the same tissue that create the bulbourethral glands in men and serve as a sexual lubricant, much like pre-ejaculate fluid.

  • Uterus – The uterus is a muscular organ about the size and shape of an upside down pear.  The uterus is suspended in the lower abdomen by ligaments.  The uterus is made mostly of muscle (it has to contract hard to force a baby out during delivery so it’s mostly muscle).  During each menstrual cycle, a glandular layer of tissue on the inside surface of the uterus known as the endometrium grows.  If pregnancy occurs, the baby attaches to this rich layer of tissue and grows in the uterus for the next nine months.  If pregnancy doesn’t occur this endometrium will die and slough off the uterus and out of the vagina (this is what a menstrual cycle or “period” is). 

  • Fallopian Tubes – Attached to each side of the upper portions of the uterus are the fallopian tubes.  These extend outwards toward the ovaries.  Conception occurs in the fallopian tubes, so sperm must swim to this point to fertilize an egg.  At the end of each fallopian tube are little finger-like protrusions called fimbrae.  These fimbrae have a wafting motion that helps steer the egg released from the ovary into the fallopian tube.

  • Ovaries – The two ovaries are located in the lower abdomen just a little below and on either side of the belly button.   The ovaries produce estrogen.  Ovaries also contain eggs (also called ova).  Approximately once every 28 days (this varies from one woman to the next), an egg will be selected for development and released.  In someone who has a 28 day cycle, the egg will develop for 14 days then be released.  If pregnancy doesn’t occur within two weeks, a new egg will be selected to grow and ovulate the next month. 




Most men know that about once a month women will have a period.  However, it’s worth going into a little detail here to see why and how that all occurs.

Unlike men who produce sperm throughout their life a girl will be born with all of the eggs she will ever have.  In fact, the vast majority will die before she reaches puberty. 

We’ve already discussed in detail that men produce thousands of sperm a second and are fertile at all times.  Women on the other hand will only release one or two eggs every month or so.  Releasing an egg from the ovary is called ovulation.  After ovulation, the egg must be fertilized within 10 hours or so otherwise the egg will die and pregnancy will not occur.  So a woman is only “fertile” for less than a day each month. 


The same hormones that produce sex hormones and trigger sperm production also help a woman produce her sex hormones and help an egg to develop.  In men, FSH and LH work in a constant 90-120 minute rhythm to trigger the testicles to make sperm.  In women, this cycle is much more complex and lasts weeks rather than hours. 


At the beginning of a menstrual period (when a woman begins to have her menstrual bleed), FSH and LH remain fairly low.  At this time, a follicle (undeveloped egg) will be “selected” to develop into a mature egg or ovum.  As the follicle develops, estrogen levels begin to increase as LH levels rise.  At a certain point, the FSH from the pituitary will surge causing the follicle to rupture releasing the mature egg.  We call this release of the egg ovulation.  


The first half of the menstrual cycle (before ovulation) is called the follicular phase.  During this phase, estrogen causes the lining of the uterus (called the endometrium) to develop with a rick supply of blood vessels in anticipation of a pregnancy.  We can think of estrogen as laying down the “bricks” that make up the uterine lining. 

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Images on this page from top to bottom include:

  1. diluck/Shutterstock.com

  2. VectorMine/Shutterstock.com