Learning About Your Body

The Male Anatomy

The Male Reproductive System (Side View)

The scrotum is the sack that hangs underneath the penis. It contains two testicles(1) which feel like two smooth oval eggs. The two testicles together are called the testes. The testes are sometimes called the gonads. The testes serve two functions, they produce the testosterone that is causing all the changes to your body and they produce sperm. The ideal temperature for the production of sperm is about one degree less than your normal body temperature. Therefore, the testicles reside outside the main part of your body. The scrotum constantly changes size to maintain the proper temperature. When you are hot, the scrotum will become loose and slightly elongated. When you get cold, the scrotum will draw up, bringing the testicles closer to the warmth of your body. Activity also changes the size of the scrotum. While you are working hard, the scrotum draws up, even if you are hot. This protects the testicles from being banged around as your legs move.

Before puberty, the testicles remained close to the body wall. After puberty, they hang within the scrotum. Sometimes one of the testicles does not drop after puberty. If this has happened to you, a visit to your local doctor would be advisable. If you look carefully, you will see that one testicle is slightly lower than the other (usually the left testicle). This is to prevent you from crushing your testicles together between your legs as you walk.

As you have already noticed, the testicles are highly sensitive to pressure. It is even mentioned in Scripture as a description of extreme anguish (Isaiah 21:3; Jeremiah 30:5-7). This sensitivity helps to encourage you to protect your only method of producing offspring. As a child, you didn’t notice this sensitivity as often because the testicles and scrotum were up against the body, giving you some measure of protection. Now that the testicles are down in the scrotum, you need to give them some added protection when playing sports by wearing a jockstrap with a protective cup. The jockstrap forces the scrotum into a smaller size and pushes the testicles against the body wall. Without a jockstrap, accidental bumps to your groin can double you over in pain. It is very tough to keep the other team from scoring a point in that position.

Internal Male Reproductive Organs (Frontal View)

Women are told to regularly check their breasts for lumps, which may be a sign of cancer. Men need to regularly check their testicles for any unusual lumps. When you shower, lightly hold your scrotum and gently feel the outer surface of the testicles. The testicles should feel smooth and oval or egg-shaped. If there are any changes, see your doctor.

To one side of each testicle is a slight bulge, which is called the epididymis(2). It feels softer than the testicles. The epididymis is a place to hold sperm produced by the testicles while the sperm matures. It takes four to six weeks for sperm to reach full maturity. The vas deferens(3) are two tubes (one for each testicle) that carry the sperm from the epididymis, up over the bladder(4) to the ejaculatory duct(6). Another name for the ejaculatory duct is the ampulla. The ejaculatory duct is another reservoir that holds the mature sperm until they are needed for ejaculation.

Next to where the vas deferens connects to the ejaculatory duct are the seminal vesicles(5). The seminal vesicles produce the thick whitish liquid that you see in your ejaculate. The liquid contains the food that nourishes the sperm once they leave your body. Once you enter puberty, the seminal vesicles constantly produce this liquid. The rate of production is strongly influenced by how often and how strongly you are aroused. As the seminal vesicles become full, you will find yourself more easily stimulated. The mildest sexual thought or touch will trigger an erection. The urge for sexual release becomes stronger. Your body releases the pressure by ejaculating semen. This is euphemistically called “night wettings” since this release usually comes at night.

A function of the prostate gland(7) is to serve as a switch. A tube leads from the bladder, through the prostate to the urethra(9), which is the name of the tube inside your penis. Normally, the prostate keeps the urinary tube squeezed shut until the time you need to urinate. The ejaculatory duct also runs through the prostate gland. The prostate is designed such that either the urinary duct or the ejaculatory duct is open, but not both at the same time. An additional function of the prostate gland is to provide fluid for the ejaculate. This fluid is the liquid that the sperm swim in. The fluid also serves to neutralize the slightly acid urine that may be left in the urethra from the last time you urinated. Finally, the prostate provides the force that squirts the semen out of the penis during orgasm.

The Cowper’s glands(8) are located just below the prostate. These glands provide a lubricating fluid that drips out of the end of the penis when you become aroused. The fluid will one day allow your penis to move more easily in the vagina of your wife when you engage in sex. The fluid also neutralizes the uric acid that remains in your urethra.

You should be aware that this fluid does contain sperm – sufficient quantities of sperm to cause a woman to become pregnant. As we will be discussing later, you can get a woman pregnant without ever ejaculating semen directly into her vagina.

The shaft of the penis contains the urethra and three sponge-like chambers called the corpus cavernosus. The urethra is the tube that your urine or your semen flows through. The corpus cavernosus are balloon-like structures, one on each side of the penis and one on top. When you become aroused, the blood vesicles near the base of your penis constrict so that blood readily flows into the corpus cavernosus, but leaves very slowly. This causes the penis to enlarge, lengthen, and become stiff. The length and size of the erect penis vary from man to man and have no bearing on how well a man can perform in sexual intercourse. Normally, the erect penis stands outward from the body and angles a bit upward. The exact angle varies with each erection. Some men have blockages in the corpus cavernosus that cause the erect penis to curl to the left or the right or to curve back on itself. If you have this problem, see your doctor about getting it corrected before you get married. Sex with this problem is usually difficult and painful.

At the end of the penis is the glans. It is a rough-textured area that gives a pleasurable feeling when lightly rubbed. The glans also expands and hardens when you are aroused. It is the rubbing of the glans that heightens the sexual tension in a man, eventually leading to an intense feeling of pleasure that is called orgasm.

The skin of the penis is very loose when the penis is flaccid (not erect). If you were not circumcised, the glans withdraws within a fold of skin. This fold of skin is called the foreskin. To understand what this is like, try this task. The next time you take off a long sleeve shirt, hold on to the cuff while you pull your arm out of the sleeve. The cloth of the sleeve will fold back on itself and cover your hand. Your hand is the glans and the fold of cloth is the foreskin. The foreskin protects the glans, keeping it moister and perhaps more sensitive. The foreskin also has nerve endings that play a role in sexual pleasure. When you are born, the foreskin is partially attached to the glans. Complete separation usually occurs around age two or three. If this separation does not occur, the boy may require circumcision.

Circumcision is cutting off the foreskin so that the glans is always exposed, even when the penis is in the flaccid state. Circumcision, when it is done in the United States, is generally done shortly after birth. There are times when a person who was not circumcised at birth may have the operation done later in life. One reason would be if the foreskin is too tight, not allowing the end of the glans to emerge when having an erection. We will talk more about circumcision in a later chapter.

Like the scrotum, the penis also changes size from moment to moment. Part of this is due to temperature changes. When the temperature is warm, the penis will lengthen. If the temperature drops, it will shrink in size. The size change can vary by a number of inches. However, the temperature is not the only thing that affects the size of your penis. Arousal plays a large part.

Male Reproductive System


Men become aroused in a variety of ways: being touched in certain ways or in certain areas, seeing something that is associated with sex, or thinking about things related to sex. When the seminal vesicles become full of fluid, you will find that the slightest stimulation arouses you.

The first evidence of arousal is the erection of your penis. In early adolescence, this happens very frequently and at the most awkward moments. You may find yourself standing in front of others, hoping that you don’t have an erection where everyone will see it, and suddenly you find yourself having one. While erections can be noticeable to others, it is far more apparent to you than to those around you. After all, you can feel the erection as well as see it. Later in life, you will gain a small measure of control over when you have an erection. However, during your early teenage years, they will come frequently with no way to prevent them.

Though the glans at the end of your penis is always sensitive to the touch, during an erection it becomes very sensitive. The lightest touch gives an extremely pleasurable feeling and your body responds to the stimulation by tensing your muscles. A cycle begins where the rubbing of the glans brings on stronger arousal and the strong arousal makes the glans more sensitive to the rubbing.

As you become aroused, fluid begins to drip from the end of your penis. The fluid continues to flow for a while even after your penis returns to its flaccid state. This is the fluid produced by the Cowper’s gland. The fluid causes embarrassing stains on your trousers whenever you become aroused. There is not much you can do about it, because you certainly cannot prevent becoming aroused. If you know you are going to be in situations that will cause you to be aroused, you can place tissues over the end of your penis underneath your underwear. The tissue will help absorb some of the fluid. It will cut down on the size of the stains if you discard the tissue shortly after the arousal is over.

The duration of an erection will vary greatly. Some men tend to hold an erection for only a short time while other men hold an erection for a very long time. The duration of each erection in any one man varies as well. Generally, the erections continue for a few seconds to a half-hour or more. If you find yourself having an erection at an inconvenient time, realize that it may take a while for your penis to return to its usual flaccid state.

Arousal is your body’s physical response to sexual stimulation. Do not confuse arousal with love; they are unrelated ideas. You will find yourself in many situations where your body will respond with an erection, but there is no way that you would say that you were in love.

The desire for sex is not wrong. God gave it to each of us so that it could be satisfied one day in marriage. The desire for sex is not a sin unless it spurs you to satisfy that desire in an unholy way.

Blessed is the man who endures temptation; for when he has been proved, he will receive the crown of life which the Lord has promised to those who love Him. Let no one say when he is tempted, “I am tempted by God”; for God cannot be tempted by evil, nor does He Himself tempt anyone. But each one is tempted when he is drawn away by his own desires and enticed. Then, when desire has conceived, it gives birth to sin; and sin, when it is full-grown, brings forth death. Do not be deceived my beloved brethren.     

James 1:12-16

Satan uses our desires to try to lead us into sin. He places us in situations where it seems that the only way out is to violate God’s law in some manner. Don’t let Satan deceive you! God has guaranteed us that there is always a way out of temptation that does not involve sinning.

No temptation has overtaken you except such as is common to man; but God is faithful, who will not allow you to be tempted beyond what you are able, but with the temptation will also make the way of escape, that you may be able to bear it.         

I Corinthians 10:13

God didn’t promise that the way out would always be easy to spot, but it is there even if we have to look hard for it. Unfortunately, when our passions are inflamed, it is difficult to think clearly. The desire for sex is very strong. Don’t fool yourself into thinking that you can go partway and resist. Sometimes the best way to keep from sinning is to avoid the temptation altogether as Joseph did in Genesis 39:1-12.

Night Wettings or Wet Dreams

As the fluid builds up in the seminal vesicles, the urge for sexual release becomes stronger in a man. At first, you may not connect the two ideas, but it is still there. Each time you become aroused, your body increases its production rate of semen. Therefore, how often your seminal vesicles fill depends on how fast your body produces semen, how often you have been aroused recently, and how strong those arousals were.

The semen cannot remain in the seminal vesicles. When the semen builds up to a certain level, your body will release semen of its own accord (though you can stop it with conscience effort). It usually happens at night while you are dreaming. You become aroused and your penis becomes erect. The glans at the end of your penis becomes very sensitive to any contact, causing your body to tense with pleasure (this is known as orgasm). Suddenly, there is a release, and the semen squirts out of your penis. The tension leaves your body leaving you feeling satisfied and very relaxed.

Some men are heavy sleepers and never wake up during one of these wet dreams. Instead they awake in the morning to find this white sticky fluid soaked through their pajamas. If the ejaculation happened early in the night, it may have dried hard and crusty. Most men release less than a tablespoon of semen when they ejaculate, but it seems as if it is everywhere when you wake up in the morning. Don’t worry about these releases; they are a normal part of your body’s functions. Simply put your soiled pajamas in the wash and wash yourself off.

While this automatic release of semen usually happens at night, it can occur anytime you are sleeping, such as during naps. The frequency of night wettings varies a lot. It all depends on how your body functions and what you have been exposed to recently. Some men experience five or more night wettings in a week at times. Other men may experience it only once a month or once a year.

You can, through conscious effort, prevent these night wettings if you wake up. Some men actively try to prevent “night wettings” because they were told that masturbation (stimulating yourself to the point of orgasm) is wrong. Night wettings are not masturbation, but many people regard them as being the same. Some people believe that a man should only ejaculate when having sex with his wife. These people believe that releasing semen, whether through “night wettings” or through masturbation, is sinful. This belief is based on a misunderstanding of the story of Onan.

Then Judah took a wife for Er his firstborn, and her name was Tamar. But Er, Judah’s firstborn, was wicked in the sight of the Lord, and the Lord killed him. And Judah said to Onan, “Go in to your brother’s wife and marry her, and raise up an heir to your brother.” But Onan knew that the heir would not be his; and it came to pass, when he went in to his brother’s wife, that he emitted on the ground, lest he should give an heir to his brother. And the thing which he did displeased the Lord; therefore He killed him also.  

Genesis 38:6-10

 The phrase “went in to his brother’s wife” means he had sexual intercourse with her. The phrasing describes the act of sex since the man’s penis is inserted into the woman’s vagina during sexual intercourse.

In those days, the wife of a man who died without heirs was given to a brother as his wife. The first child that they had would be counted as his brother’s heir. Onan was given Er’s wife to produce an heir for his brother. However, Onan didn’t want his brother to have an heir. Therefore, when he went to have sex with Tamar, he withdrew his penis before ejaculating semen so that it spilled on the ground. God punished Onan for his sin, but what was the sin? Onan’s sin was not that his semen spilled on the ground. His sin was avoiding his duty to produce an heir for his brother. A second reason that this passage does not condemn “night wettings” or masturbation is that Onan was engaged in the act of sex. He was not having a “night wetting” nor was he stimulating himself to the point of releasing semen. What Onan was doing was practicing a form of birth control when he should not have been.

Night wettings are mentioned in the Old Testament in a number of places (Leviticus 15:16-18; 22:4Deuteronomy 23:10-11Exodus 19:15, and I Samuel 21:4). When a man had an ejaculation, he was considered unclean until the next evening. He was required to wash and anything his semen came in contact with. The Israelite laws regarding uncleanness did not imply that the man had sinned. The laws were a way to encourage healthy practices among the Jews. Both men and women had to separate themselves whenever there were emissions from their bodies. These laws cut down on the spread of diseases among the Israelites.

Preventing ejaculation by blocking the end of your penis can be painful. If you held the end of your penis closed just before ejaculating, the semen will be forced backward through the prostate and into your bladder. This stretches your prostate, causing extreme discomfort, if not downright pain. For a few days, you will experience pain when urinating and your urine will have a cloudy look. If the discomfort does not begin to go away in a few days, your inflamed organs may have picked up an infection. See your doctor immediately for treatment. Do not put it off because you are embarrassed to tell how the infection came about.

Instead of working against the natural course of your body, accept the fact that “night wettings” are a normal part of your body’s function – needful to keep you healthy. This does not mean you should engage in masturbation, but neither should you prevent ejaculation at night when you feel the urge for sexual release comes upon you. Since the build-up of semen increases your desire for sex, a side effect of “night wettings” is a slight decrease in your desires. This gives you some help in resisting Satan’s temptations.

Study Questions

Male Reproductive Organs - Side View, Unlabeled
  1.  Using the cut-away drawing of your sex organs, name as many parts as you can:
    1. _
    2. _
    3. _
    4. _
    5. _
    6. _
    7. _
    8. _
    9. _
  2. Why do your penis and scrotum constantly change size?
  3. Why does one testicle hang lower than the other?
  4. What do the seminal vesicles produce and what happens when they become full?
  5. What happens inside your body to cause an erection?
  6. What is circumcision?
  7. What causes arousals? How do you know you are aroused?
  8. What are night wettings? What causes them?
  9. What is masturbation?
  10. What was Onan’s sin?

Class Discussion

  • Can masturbation be a sin?
  • Have you noticed something about your body that you don’t understand why it functions as it does?
  • Are you experiencing a problem, but not certain if you should see a doctor?