Testes

Composed of the same material that ovaries are formed from, a man’s testicles originally develop in his abdomen. About two months before his birth, though, the two testes descend from the abdomen into the scrotum, which acts as a support sac to the testicles. The main function of testicles is two-fold: they are responsible for producing sperm as well as the hormone testosterone. The testicles are made up of seminiferous tubules (hundreds of tiny tubes), Leydig cells (which is where testosterone is produced), and Sertoli cells (which are responsible for nurturing immature sperm cells).

Because the testicles need to remain about 1°C cooler than normal body temperature, the scrotum helps to regulate the temperature of the testes. When exposed to cold air, the scrotum contracts to keep the testes warm but hangs lower when it is hot outside.

Epididymis

Found at the top of the testes, the epididymus is a set of tightly coiled tubes. How tightly coiled? Well, if you stretched it out, the epididymus would reach 20 feet long. The epididymus acts as a temporary storing place for sperm as they continue to mature. It is within these tubes that sperm gain the ability to move.

This long tube extends from the epididymus in the testicle, up, over the bladder and finally ending at the seminal vesicles. The vas deferens acts as both a passageway for the sperm as they exit the body and as another storing place as the sperm wait to be ejaculated.

Seminal vesicles

These two pouch-like sacs are found behind the bladder. The seminal vesicles add an alkaline fluid that makes up 30% of the total semen volume. This secretion helps give the sperm energy, thereby giving their motility a boost.

Prostate gland

This gland sits just below the bladder and contributes about 60% of the total semen volume. This alkaline secretion is similar to the fluid produced in the seminal vesicles and is necessary to the sperms’ survival by helping neutralize the naturally occurring acids in the urethra and the vagina.

Cowper's glands

Positioned just below the prostate, these are two small glands that produce about 5% of the alkaline secretions that make up semen.

Ejaculatory ducts

These are two short ducts that connect the prostate gland to the urethra. The joining of the two vas deferens makes up the ejaculatory ducts.

Urethra

Used as the final passageway for both semen and urine, this tube starts at the bladder, goes through the prostate and extends to the tip of the penis. When a man climaxes, the prostate closes off the bladder to prevent any urine from joining the semen.

Penis

The method of delivery for sperm, this organ is made up of veins, arteries and spongy tissue. When a man becomes sexually aroused, the arteries dilate allowing the tissue to become engorged with blood. This causes the penis to stiffen and become erect.

The Hormones

Gonadotropin Releasing Hormone (GnRH): Originating in the hypothalamus in the brain, GnRH is responsible for signaling the pituitary gland to start production of follicle stimulating hormone (FSH) and lutenizing hormone (LH).

FSH: This hormone is responsible for stimulating and maintaining sperm production.
LH: This hormone is responsible for getting the production of testosterone started.
Testosterone: Produced in the Leydig cells in the testes, this hormone helps with sperm production but it is mainly responsible for male maturation (the deepening of the voice, sex drive, growth and development of the sex organs).

Making It All Work

At birth, males have simple round cells contained within their seminiferous tubules. This is the most primitive form of sperm. During puberty, stimulation by testosterone and other hormones cause the cells to divide, thereby beginning the maturation process of sperm. The sperm cells will divide and mature until they begin to resemble tadpoles, with an oval head and long, thin tail. Contained within the sperm head is all of the genetic information that a man contributes to his child. The tail is used to propel the sperm along its journey.

Once the sperm has developed its head and tail, it is shuttled along to the epididymus. Here it will enjoy a three-week stay by the end of which it will have gained the ability to move. Next, the sperm move through the vas deferens to the seminal vesicles where they stay until they are ejaculated. All along this trip, the sperm will be provided with fructose, a type of sugar, to give it energy as it travels along.

During ejaculation, fluid from the prostate, seminal vesicles, and Cowper’s gland combine with the sperm to make semen. This will be expelled from the body during orgasm. For fertilization of the female egg to occur, it is necessary to ejaculate inside the vagina.

Anywhere from 250 million to 1 billion sperm are produced and ejaculated at one time in a healthy male. However, only about 200 of these will actually make it up through the vagina, cervix and uterus and into the correct fallopian tube. From this drastically reduced group, only one sperm will actually be able to fuse together with the egg to create a child. In total, it takes a few days for sperm to make the trip through the female reproductive system to the egg.