Infertility: the egg and the sperm

How the egg is fertilized
An egg is usually fertilized by sperm within the fallopian tubes - but only if the woman has sex with a man around the time the egg is released. The sperm must penetrate the egg to fertilize it.

Sperm can survive for six days after entering a woman's vagina and can fertilize the egg at any time during this period. However, research shows that fertilization is most likely to occur two days before or on the day the egg is released. The fertilized egg then moves on to the uterus, where it implants and grows into an embryo, and pregnancy results.

The Unfertilized Egg

If the egg is not penetrated by sperm, it lives for 12 to 24 hours. The egg and the bloody lining of the uterus then slough off, traveling out of the uterus, the cervix and vagina - a process called the woman's menstrual period.

Reproduction In A Man

Men have four primary hormones involved in reproduction. They are:

• gonadotropin-releasing hormone (GnRH).
• follicle stimulating hormone (FSH)
• luteinizing hormone (LH).
• testosterone

Here is how the hormones work:

• In a man, the brain's hypothalmus first releases gonadotropin-releasing hormone (GnRH).
• GnRH stimulates the pituitary gland to produce two hormones - follicle stimulating hormone (FSH) and luteinizing hormone (LH).
• These hormones regulate the production of sperm and the release of the male hormone testosterone, all of which takes place in the male testes, located in the scrotal sac.

The Production of sperm

Sperm begin life in the testes in cells called Sertoli cells.

• At the beginning of a sperm's life cycle, hormones develop its head and tail.
• The sperm then escapes from the Sertoli cell into the epididymis, located behind the testes.
• For three weeks, a sperm travels through the epididymis in an energizing fluid containing fructose. As the sperm swims through this fluid, it matures and acquires the ability to swim and move back and forth.
• A mature sperm has a head that contains the man's DNA - his genetic material - and a tail that rapidly moves from side to side, propelling it forward.

Ejaculation

When a man ejaculates during sex, muscular contractions push the sperm out of the epididymis to channels called the vas deferens. The sperm then move to the ejaculatory ducts and out the urethra (the passage through which urine and semen are passed from the body).

• Just before ejaculation, the sperm in the ejaculatory ducts mix with fluids that come from the prostate gland and from glands called the seminal vesicles, creating semen.
• During orgasm, the seminal vesicles push the semen forcefully out into the urethra.
• A muscle in the bladder also locks shut to prevent the semen from traveling backward into the bladder and mixing with urine.
• The semen moves from the urethra to a holding area at the bottom of the penis, where muscles propel it out of the penis.

How a sperm fertilizes the egg

Of the 100 to 300 million sperm released when a man ejaculates, only about 40 survive the trip through the acidic environment of the vagina and cervix. The woman's thick cervical mucous can also be a barrier. But during ovulation, the woman's mucous thins and allows the sperm to travel more freely.

After it bores through the cervical mucous, the sperm trigger the acrosome (a special membrane located on their heads), and it dissolves and releases special enzymes. These enzymes allow the sperm to penetrate the tough coating surrounding the egg in the fallopian tubes. Only one sperm ultimately fertilizes the woman's egg.

Nice To Know: What should I do if I think I am infertile? If you've had more than a year of regular sex without birth control and you haven't achieved a pregnancy, it may be time to see a doctor. If a year hasn't passed yet, a good strategy is to plan to have sex during the days the woman is ovulating. To find the days when she ovulates, a woman can take her temperature by mouth or in the vagina with special thermometers available in drugstores. Her temperature will rise slightly on the days she ovulates.

Facts About Infertility:

• It's a myth that infertility is always a "woman's problem." Half of all cases of infertility result from problems with the man's reproductive system.
• The best protection against infertility is using a condom while you are not attempting to conceive a child. Condoms protect against sexually transmitted diseases, a major cause of infertility.
• Of couples that seek medical treatment for infertility, 20 percent conceive before the treatment actually begins. One reason may be that anxiety about infertility may have contributed to the fertility problem, and contacting a doctor provides emotional relief.
• Fifty percent of infertile couples conceive within two years of starting treatment.
• A woman's temperature rises about 1 degree Fahrenheit during the days she is ovulating (producing eggs). By taking her temperature every morning with a special thermometer, a woman and her partner can chart the rises and falls in her morning temperature. They can then plan intercourse for the days she is ovulating--her most fertile time.