The Male Reproductive System



The sack under the penis contains two testicles. On boys, the scrotum is small and compact, but after puberty, it expands to accommodate the increasing testicle size and to provide more surface area to cool the testicles. In order for the testicles to properly produce sperm, the organs must be kept 1 to 4 degrees cooler than the body. To keep the testicles in the proper temperature range, the scrotum constantly changes size. If the temperature is too cool, the scrotum contracts, bringing the testicles closer to the warmth of the body. The scrunching of the scrotum also thickens the walls of the scrotum and lessens the surface area, which minimizes the heat loss. If the temperature is too warm, the scrotum hangs loosely, bringing the testicles farther from the body. The expanded size exposes more surface area for excess heat to be dissipated.

The scrotum will also draw up during physical activity, such as running or during sexual intercourse. This reflex protects the testicles from being knocked around.


The two smooth, oval-shaped organs within the scrotum are called the testicles. They serve two major functions. First, they produce the hormones required by the male body. Testosterone is the most commonly known hormone, though there are others. Second, the testicles produce the sperm needed to produce a child.

Each testicle hangs on a cord in the center of the scrotum. The left testicle generally hangs slightly lower than the right testicle. This is to prevent the testicles from knocking against each other when you walk. The blood supply for the testicles twines around the cord. Sometimes a testicle will twist on the cord, causing the blood supply to be pinched off. For some reason, if it happens, it is more likely to occur in teenagers than adults. When it happens, the man will feel excruciating pain in his abdomen, where the nerve endings for the testicles are located. If the problem is not corrected within 4 to 12 hours, the testicle will die. Hence, the torsion of a testicle is considered a medical emergency. It generally requires surgery to untwist the testicle.

The most common cause of torsion is a blow to the pelvic region. This is the reason men are encouraged to wear a jockstrap when playing sports. The strap holds the scrotum tight against the body and helps to prevent the testicles from twisting.

The testicles are extremely sensitive to being hit. This is God’s way of reminding the man to protect his ability to have children.

A rare form of cancer attacks the testicles. It occurs more commonly in young men in their twenties and thirties than in older men. For this reason, men are urged to check their testicles monthly for signs of cancer. The best time to check is during a hot shower when the scrotum is loose. Gently feel the surface of each testicle. It should be a smooth oval shape. Testicle cancer will feel like a hard lump on the surface of the testicle. Don’t confuse the epididymis for cancer. The epididymis is a soft area on the upper-back portion of each testicle.

The testicles in the average healthy male produce about 100 million sperm cells per day. Each ejaculation contains about 500 million active sperm cells in a healthy man. While this may seem like a large quantity, all these sperm is less than 1% of the total fluid ejaculated.


The epididymis is attached to the upper portion of each testicle. It serves as the incubation area for the sperm after they leave the testicle. The epididymis consists of 15 to 20 bundles of tubes, jumbled together in a maze-like structure. If the tubes were stretched out to their full length they would each be about 20 feet in length. It takes about 4 to 6 weeks for the sperm to move through the epididymis, during which time the sperm “ripens.”

Vas Deferens

These are long tubes that carry the mature sperm from the epididymis, up over the bladder and to the ejaculatory duct.

If a man decides to have a vasectomy, so he will be unable to produce children, an inch-long section of each Vas Deferens is removed surgically and sealed. The surgery does not impact the testicle’s ability to produce hormones and it does not prevent a man from having sexual intercourse. It simply prevents sperm from being mixed into the semen the man ejaculates. Since the sperm is unable to leave the testicles, the body develops antibodies to the sperm and reabsorbs them as they are produced.

Seminal Vesicles

These organs produce a thick, whitish fluid, known as semen. The fluid is rich in sugars which activate and feed the sperm just before they are ejaculated. Semen is constantly produced and stored by a man’s body. The rate of production is directly proportional to the frequency that a man is aroused. The quantity released in ejaculation is less than a tablespoon, of which less than 1% is composed of sperm.

Prostate Gland

The prostate gland serves several purposes. First, it produces additional fluids, which are added to a man’s semen during ejaculation. The fluids help keep the sperm healthy and alive. In addition, it contains muscles that control the flow of fluids through the urethra. In a sense, these muscles serve as a switching mechanism. In a normal mode, urine is allowed to flow from the bladder and the passage to the ejaculatory duct is closed off. When a man is sexually aroused, the passage to the bladder is closed off and the passage to the ejaculatory duct is opened. Because of this, a man is not able to urinate when he is sexually aroused. A third function of the prostate is also muscular; the muscles in the prostate are what propel the semen through the urethra during ejaculation.

Infections in the prostate may cause the gland to swell and interfere with the flow of urine and semen through the urethra. For some elderly men, the prostate gland may continue to grow and cause difficulties in urination. Prostate cancer is the most common form of cancer in elderly men. It, too, is characterized by a growth of the prostate, though in the case of cancer, the growth is rapid and if left untreated will spread to other organs of the body.

Cowper’s Gland

Two small glands (about the size of peas) beneath the prostate gland and on each side of the urethra also produce fluids for sexual intercourse. The gland is also known as the bulbourethral, though most people refer to it as the Cowper’s gland – Dr. Cowper being the one who discovered the function of the gland. The clear fluid begins to flow when a man is sexually aroused. It flows through the urethra and drips from the end of the penis. This fluid contains ingredients which neutralize the acids normally left in the urethra from urine. It is also very slick, providing a small amount of lubrication for intercourse.

The amount of fluid produced varies from man-to-man and situation-to-situation. It can be embarrassing at times to find a wet stain on your trousers as a tell-tale indicator of your thoughts.

Since the fluid is flushing the urethra and prostate opens the pathway to the ejaculatory duct in preparation, it is possible, even likely, for the fluid from the Cowper’s gland to contain a small quantity of sperm. Because of this, withdrawing before ejaculating is never one-hundred percent effective in preventing pregnancy. While the odds are against it, it just takes one sperm to fertilize an egg.

Penis - Corpus Cavernosum and Corpus Spongiosum

The penis is a man’s most prominent feature. It encloses three structures: two corpus cavernosum run parallel along the top of the penis and the corpus spongiosum is at the bottom-center of the penis. The urethra runs through the center of the corpus spongiosum. These structures contain spongy chambers which inflate with blood when a man is sexually aroused. The result is much like a balloon which is limp when deflated and stiff when inflated.

When flaccid, the average man’s penis is about two to three inches in length though the actual length varies with temperature. When fully erect, the average length of a man’s penis is five to seven inches long and five to six inches in circumference. These sizes are averages. The actual size of any particular man can vary greatly. Though many men find it hard to believe, the actual size of the penis has little to do with sexual performance or the ability to give sexual pleasure to a man’s wife.

During arousal, small muscles along the veins close off the exit points for the blood in the penis. Simultaneously, the arteries bringing blood into the penis widen. The result is an inflation of the penis both in length and in width. The amount of inflation depends on the strength of the arousal. A cord at the base of the penis causes the erect penis to angle upwards.

Erections normally last from a minute to a half-hour or more. Since blood is pooling in the penis, the tissue in the penis is not receiving fresh oxygen from the blood. If an erection lasts too long, a man experiences an aching feeling in his genitals – sometimes called “blue balls.” If an erection is not lost within several hours, the genitals can become extremely painful.

About one percent of men experience Peyronie’s disease. This is when scar tissue forms in one of the chambers, blocking the flow of blood and preventing complete inflation. The result is an erect penis that curves to the left or right. Usually, the condition clears up on its own within one year. If the curve is severe, it can make intercourse difficult and possibly painful. If the condition does not clear up on its own or is particularly painful, the man should visit a urologist for treatment.

The cause of Peyronie’s disease is thought to be due to the bending of the penile shaft when it is erect. Since men often arise in the morning with a full erection, they should avoid forcing their erect penis to bend downwards to urinate. As difficult as it seems, men should wait until the erection passes before using the restroom.

Penis - Glans

The head of the penis is called the glans. It is a rough, textured area that contains many nerve endings that are sensitive to touch. When a man is aroused and his penis becomes erect, the glans also enlarges. The swelling in size causes the textured skin to stand up, making the area highly sensitive to touch.

The sole purpose of the glans is to give sexual pleasure. While touching and light strokes are highly pleasurable, hard, dry rubbing can be painful because the skin is too sensitive.

Penis - Foreskin

The foreskin is a double fold of skin at the end of the penial shaft which covers the glans. To imagine how this works, try grabbing the cuff of a long-sleeved shirt with your arm in the sleeve. As you pull your arm inwards the loose folds of cloth double over and over your hand. The foreskin operates in the same fashion.

Circumcision is an operation that removes the foreskin by cutting around the base of the overlap and then removing the excess skin. Currently, about half the men in the United States are circumcised at birth. On a circumcised man, the glans is always exposed. On an uncircumcised man, the glans is covered by the foreskin when the penis is flaccid but is exposed with the penis is erect.

God, at one time, required the descendants of Abraham to be circumcised. It was not for medical reasons but as a sign of the covenant between God and these people (Genesis 17:10-14). This covenant ended and with its end, circumcision is no longer required (Galatians 5:2-6; 6:15). By itself, circumcision serves no useful purpose. The reason it continues today in the United States is that everyone else is circumcised and they don’t want embarrassments in the locker rooms or they want their boys to match their father. At one time it was believed that circumcision decreased the incidence of bladder infections. Even though bladder infections are fairly rare, it can all but be eliminated if uncircumcised men periodically bathed underneath their foreskin. Whether you are circumcised or not makes no difference (I Corinthians 7:18-20).

When a boy is born, the foreskin is typically attached to the glans. Generally, by the age of 3, the glans and foreskin separate and the foreskin can be retracted towards the abdomen to expose the glans. The foreskin should not be forced to detach from the glans on uncircumcised boys. For some boys, the attachment remains until puberty. It is possible for these boys to experience some discomfort when their first full erection causes the glans and foreskin to separate. If for some reason the glans and foreskin do not separate, a visit to the doctor will be called for.

Another foreskin problem is phimosis, which is a tight foreskin that prevents the foreskin from retracting, This condition occurs in less than 2% of all uncircumcised males. Since the foreskin can remain attached up to puberty, it cannot be properly diagnosed until after a boy achieves the ability to have an erection. The condition is treatable without resorting to full circumcision.

Another rare condition is called a frenulum breve. The frenulum is the area under the penis where the foreskin attaches underneath the opening of the urethra. In some men, this band of skin is too short, causing pain during erections. While it can occur in a circumcised male, it is more likely to be found in an uncircumcised male. Even then, it is typically rare. Once again, the condition is treatable without the need for a full circumcision.

The reason for mentioning these conditions is that young men do not normally discuss difficulties in achieving erections. In fact, if a young man experiences pain on erections, it doesn’t take long for his body to avoid having erections. The young man will not realize there is a problem until after his marriage when he finds out that his first attempt at sex is very painful. If you experience discomfort during an erection, you should consult a urologist to be sure your first time for intercourse is pleasurable.


Arousal is the physical response to the desire for sex. It is evidenced in the male body by the erection of the penis.

All men experience infrequent stiffening of the penis from birth, but after reaching puberty men begin to have erections. The length and width of the penis increase significantly as blood fills up the three chambers in the penis. During adolescence, erections occur frequently for no apparent reason. Just as an infant moves his limbs as he learns to control their movement, so does the teenage boy’s body go through a period of learning to control erections. It is often a source of embarrassment for a teenager. It appears that his penis has a mind of its own and will stiffen at the worse possible times. Since erections are caused by the tightening of small muscles around the veins of the penis, any source of tension can potentially trigger an erection – such as standing before the class to give a presentation.

Eventually, the body learns how to control erections. Arousals are limited to things related to sex, then more specifically to females, and eventually to a man’s spouse. It is along this path that a man is susceptible to the perverted ideas of sex, such as homosexuality. Since the body is being trained for sexual responses, the young man can be easily encouraged to believe he has a desire for male sex. What he probably does not realize is that his body is easily triggered into arousal by any sexual thought or action. He can be easily persuaded that his normal reaction is an abnormal desire for homosexuality.

Along with arousal is the flushing of the penis with fluid from the Cowper’s glands. The amount of fluid that is released varies from man-to-man, but it can be enough to leave a stain on a man’s trousers. As with erections, there is not much that a man can do to control his physical responses. It is the same as saying you can control your hunger or thirst by mere conscious thought. This is the way God designed our bodies. While we may not control the response, we can control our thoughts and our actions. The desire for sex is not wrong, but it is wrong if it spurs a man to satisfy that desire in an unholy manner. Satan uses the desires of our bodies against us, to tempt us to sin against God (James 1:13-16). Since the desire for sex is very strong, we must be on guard that we are not lured into sin.


The seminal vesicles constantly produce semen and eventually, that fluid must go somewhere. The male body has two methods for dealing with excess semen. Every day, men experience erections, especially at night when most men will have four to five erections while they sleep. During the erection, the prostate closes off the bladder and opens the pathway to the ejaculatory duct. A small amount of semen may drip out at this time. The next time the man urinates, it is flushed out of his system.

For many men, though, this doesn’t release enough of the built-up semen. During one of the nighttime erections, the body goes through the sequence of sex and semen is ejaculated. It is commonly called a nocturnal emission or a wet dream. Generally, a teaspoon or two of semen is released. The frequency of these emissions can vary from rarely, or not at all, to several times a week.

By the way, this is why most men wake with an erection. The full bladder presses on the seminal vesicles which trigger arousal. Since the prostate closes off the bladder during arousal, it probably also aids in bladder control. It would explain why young boys who have trouble wetting their bed at night grow out of the problem after reaching puberty.

The emission of semen is mentioned several times in the Scriptures (Leviticus 15:16-18; 22:4; Deuteronomy 23:10-11; Exodus 19:15; I Samuel 21:4). Most people are surprised to find these passages in the Bible. We often hear about the passages which explain that a woman, during her monthly period, was considered unclean for a week. It seems unfair that something a woman cannot control would make her unclean. However, it surprises many people to learn that men lived under a similar restriction. Whenever semen was released, whether it was during the act of sex or from a nocturnal emission, the man was unclean until the evening of the next day. Whatever came in contact with the semen was also unclean. At the end of the day, the man would bathe himself and whatever came in contact with his semen. He then was considered clean once again. Since the frequency of nocturnal emissions can vary between men, it is possible that some men spent a good portion of the month being unclean.

While a man was unclean, he could not go to the temple. If he was a priest, he could not serve in the temple. If he was in the army, he could not go to battle. This explains the actions of Uriah in II Samuel 11:6-13. David wanted to hide his sin with Bathsheba, the wife of Uriah, by having people think that the child was Uriah’s. To David’s annoyance, Uriah refused to sleep with his wife when he was called back from the battle. Quite simply, Uriah wanted to be ready to return to battle at a moment’s notice if there was a need for him. If he had sex with his wife, he would be unclean until the next evening. He would be unavailable to serve, which he thought was too great a sacrifice to make while the ark and his brethren were in potential jeopardy.

At some point in a man’s adolescent years, he discovers he can stimulate himself to orgasm. The common belief is that most, if not all men, experiment with masturbation at least once. Such an assertion would be difficult to prove as what a man says about sexual matters and what he actually does may be two entirely different things.

For Christians, the question is whether masturbation is sinful and here I have difficulties because there isn’t a passage that specifically mentions masturbation or describes the act of masturbation. Some people turn to the passage that discusses the sin of Onan in Genesis 38:6-10. However, if you read the passage, you will find that Onan was practicing birth-control by withdrawing during the act of sex before he ejaculated. Onan was engaged in intercourse, not masturbation. The sin for which he was punished was not that of spilling his semen on the ground, but for refusing to raise up an heir for his brother, Er.

It is possible that masturbation is included in some of the broader statements concerning a man having an emission of semen. A few specifically mention the emission coming from nocturnal emissions or during the act of sex, but others don’t specify how the semen was emitted. We must remember that such a conclusion is not a necessary inference. It is an assumption, and assumptions are not proof.

While we cannot discuss a passage which directly mentions masturbation, there are passages which deal with problems often associated with masturbation. Those who engage in masturbation often stimulate themselves with sexual thoughts. A Christian must be careful not to allow his thoughts to cause him to desire what is unlawful for him to do. For example, admiring a pretty woman, as you would a beautiful sunset, would not be wrong, but for a man to look at a woman with the desire to have sex with her when they are not married is wrong. Jesus said there is no difference in desiring to break the law of God and actually doing it (Matthew 5:28). For this same reason, pornography is sinful. It generates a sexual desire for people to whom you are not married and sex outside of the marriage covenant is sinful (Hebrews 13:4).

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