The Male Reproductive System
The male reproductive system begins in the scrotum, which is the sack behind the penis. This sack contains two testicles, which manufacture a man’s sex cells, called sperm, and the male sex hormone, called testosterone. The testicles feel solid, but a little spongy; like hard-boiled eggs without the shell. They hang from a cord called the spermatic cord.
The testicles produce sperm best when they are at a temperature which is a few degrees below the normal body temperature. This is why nature has designed a scrotum—so that the testes can hang outside the body to keep them cool.
The testicles start producing sperm when a young man reaches puberty. This is in response to the male sex hormone, testosterone, which starts being produced at this time. The testes keep on producing sperm for the rest of the man’s life.
The sperm are produced inside several hundred coiled microscopic tubules called seminiferous tubules present in the testes. These tubules converge and collect in the form of a delta (the mouth of a river) near the upper part of the testis called the rete testis, which then empties through a series of very small ducts, called the efferent ducts, out of the testis towards the epididymis. The epididymis is an amazing structure—it is a very long tiny tubule, which runs back and forth in convolutions and loops to form a tiny compact structure with a head, body and tail that ’sits like a cap on the top of and behind the testis. The tail of the epididymis then leads to the vas deferens—a thin cordlike muscular tube, which is part of the spermatic cord and which ends at the ejaculatory duct in the prostate. The prostate is a small, walnut-sized gland, which is located at the base of the bladder; and through it runs the urethra. In the prostate the ejaculatory duct is joined by the seminal vesicle ducts and they all open into the prostatic part of the urethra, which, in turn, leads to the urethra in the penis.
Mature sperm take about 75 days to develop in a process called spermatogenesis. Sperm production takes place as though the sperm were on an assembly line, with the more mature sperm being passed along towards the centre of the tubule, from where they swim towards the efferent ducts of the testis towards the epididymis. This assembly line can be very “temperamental”; things may often go wrong, leading to low sperm counts.
When the sperm leave the testis, they are not yet able to swim on their own. They acquire the capacity to do so in their passage through the epididymis, which acts like a “swimming school” for the sperm. They spend between 2 and 15 days here during which they attain maturity and fertilizing potential. Sperms are propelled along this tunnel by frequent contractions of its thin muscular wall.
Most of the mature sperms are then stored at the end of the epididymis, where they wait in order to be rushed through the vas deferens and then ejaculated at the time of orgasm.
During ejaculation, the muscles of the epididymis and vas deferens contract to propel the sperm into the ejaculatory duct. Here the sperm is joined by the secretions of the seminal vesicles and the prostate gland (which contribute the bulk of the seminal fluid) to form the semen. The powerful muscles surrounding the base of the urethra • then cause the semen to squirt out of the penis at the time of orgasm. The remarkable aspect of this system is that semen and urine never mix in a healthy male (even though the final passage for both is common). This is because the bladder sphincter muscle contracts during sexual stimulation, thus closing the exit from the bladder to the urethra during ejaculation, thereby preventing urine from leaking forward out of the bladder during sex and also preventing semen from accidentally going backward into the bladder.
What about the relationship between penis size and fertility? Most men equate their fertility potential with their virility—and therefore with the size of their penis. However, the size of the penis has little to do either with fertility potential or with sexual ability. (In any case, if you worry that your penis is too small, you’re not alone —most men think that their penises are too small!)
During ejaculation, about one teaspoon of semen spurts out of the penis. Semen has a milky white color, with the consistency of egg white. Sperm account for only about 2 % to 3 % of semen. Most of the semen consists of seminal fluid, i.e., the secretion of the seminal vesicles and the prostate gland, which provide a vehicle for carrying the sperm into the vagina.
A normal ejaculation contains 200 to 500 million sperm. How can so many sperm fit into only a teaspoon of semen? Simple — sperm are very tiny. If one average ejaculation filled an Olympic size swimming pool, each sperm cell would still be smaller than a goldfish. Sperms are the smallest living cells in the human body and the egg the largest. Basically, sperms are designed so that they can deliver their contents—the male genetic material—to the egg. This is why sperms are designed like projectiles—the male DNA is found in the chromosomes in the sperm head nucleus, and the tail propels the sperm up towards the egg.
Sperms are very fragile. Consequently, very few are able to survive the hazardous swim through the female reproductive system in order to reach the egg. This is why a male produces such a large number of sperm. Perhaps the reason for this is also an “evolutionary hangover”—a legacy from our past. To amplify: female fish deposit eggs on the seabed and the male fish then sprays his sperm into the sea water. The wastage of sperm in the water is tremendous, and this is why male fish need to produce millions of sperm, in order to ensure that at least some sperms reach the eggs.
What happens to the sperm if you do not indulge in sex for many days? Unfortunately, you cannot store up sperm. If ejaculation does not occur for many days, the sperm in the reproductive ducts simply die. This is why a sperm count carried out after many days of abstinence from sex shows a high number of dead or immotile sperms. But there is no need to be discouraged by this. The good news is that just like you cannot store your sperm, you cannot run out of sperm either—masturbation and sexual intercourse cannot “use” sperm up. The body keeps producing sperm as long as a man has even one normal testicle.