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.