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Innies & Outies: The Penis, Testes and More

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There's a whole lot more to this anatomy than meets the eye. Sure, you may know where the penis is... but what about the rest of it? This simple guide walks you through the external and internal reproductive and urinary anatomy for most penis-bearing folks.

Consider The Penis

Whether you give it a name or not, the ol' one-eyed wonderworm seems like a pretty simple critter from the outside, but it's actually a bit more complicated than many people think.

On the outside, there are five major things you can see: the glans or head, the corona, the frenum, the urethral meatus, and the shaft. For those who are uncircumcised, there is a sixth, the prepuce or foreskin.

Let's take it from the top.

At the tip of the penis you will find the urethral meatus, the opening of the urethra, where urine comes out when you urinate. It's also where pre-ejaculatory fluid and semen come out of the penis. The urethra inside the penis has both a urinary function and a reproductive one. This is not the case for people who have a vulva: urethras and vaginas are entirely separate orifices.

The urethral meatus is usually located in the center of the head or glans of the penis, the mushroom or helmet-shaped, somewhat bulbous, section that composes the end of the penis.

The little ridge that runs all the way around the bottom of the head of the penis is called the corona, and just below the spot on the underside of the penis where the corona makes a little V shape is the frenum (sometimes called the frenulum). For some, the tiny little patch of skin that is the frenum is the most intensely sensitive part of the whole penis, but that's not always the case. For many, the glans is also very sensitive, and for those who are uncircumcised, the foreskin as well is sensitive, being very rich with nerve endings, as are the areas beneath stimulated by the foreskin.

The shaft of the penis is exactly that - the shaft, the part that makes up the part of your penis that isn't the glans. When the penis is hard, it is common to see veins just under the skin. The veins can look kind of bulgy and weird sometimes, but as long as they are not painful in any way, that's perfectly normal.

If you are NOT circumcised, you will have what's called a prepuce or foreskin. This is a loose tube of skin, chock full of nerve endings, that grows out from the shaft of the penis just below the glans and which normally covers the head of the penis when it is not erect - one guy I know says his always makes him think of a little sleeping bag for the penis. All people born with penises are also born with foreskins, but some (the majority, in North America, but a great minority elsewhere in the world) foreskins are surgically removed when a baby is a few hours or days old in a process called circumcision. It is normal to have a foreskin, and it is also common to not have one. However, in 1999, the American Pediatric Association finally made clear that there is no medical basis for infant circumcision.

If you do have a foreskin, the foreskin can be pulled back, away from the head of the penis, and this should be pretty easy to do. If it's difficult to do, or painful, or impossible, talk to a doctor. You need to pull back (also called retracting) the foreskin in order to put on a condom correctly. Also, if you cannot retract the foreskin adequately, sexual activities (including masturbation) can be painful.

The skin of the penis can sometimes be several shades darker than the skin of the rest of your body, either all the time or just when the penis is hard. That's totally normal. It's also normal to have the penis change color somewhat when it gets hard. It is common for penises to turn red, brown-red, or even purple! The coloration should return to normal once the erection goes down.

It's also common to have some pubic hair growing on the shaft of the penis. And of course, anywhere you have hair follicles and sweat glands, it is possible to get a pimple or zit. If you have a sore or blemish on your penis and it looks like a pimple, chances are good that it might be just that, particularly if it is on the bottom third of your penis, where there is most likely to be some pubic hair. If it doesn't go away in a few days' time, though, or doesn't seem like a pimple, see a doctor. Any sore that looks like a wart, a cold sore, a sunburn, or a rash on the penis needs to be looked at by a doctor, immediately.

Life On The Inside: What's Inside Your Penis

Now that you know your way around the outside of the penis, let's look inward. You might already know that the penis gets erect because of blood, but might not know where that blood goes. It doesn't just fill up the penis like a water balloon! When blood flows into the penis to create an erection, it goes into and fills up two spongy bodies of tissue that run the length of the penis. The corpus cavernosum runs along the top of the penis, and another similar body called the corpus spongiosum runs along the urethra. Both the corpus cavernosum and the corpus spongiosum extend a little way into the body, which is what gives the leverage so that, when these spongy structures are filled with blood, they get stiff and the penis becomes both hard and erect.

Many people associate getting an erection - also known as a hard-on, boner, woody, or by various other names - with being ready for sex or ready to feel sexual pleasure. Truth is, erections can and often do happen quite a few times every day for no particular reason, and certainly not because anything sexual is going on. It just happens. If you're not interested in any kind of sex at the moment, including masturbation, you can just ignore it, and it'll go away. Also, your penis doesn't have to be hard in order for you to feel sexual pleasure. There are many kinds of sensations that can feel sexually good. An erection is not a prerequisite.

The urethra is the long tube that runs the length of your penis and connects to several organs inside your body. Everything that comes out of your penis travels through the urethra - urine, pre-ejaculatory fluid (precum), and semen. The urethra is a very sensitive and delicate duct, and can easily get scarred or infected if you treat it roughly. Sometimes people are curious about how it would feel to put objects up their urethras. This is a bad idea: it can cause serious medical trouble and can even end up requiring surgery on the penis. If you treat the urethra as a one-way street, you should be fine.

Urethra troubleshooting: if your urethra ever burns or itches, particularly when you are peeing, or if you see greenish, yellowish, foamy, bloody, or foul-smelling discharge from your urethra, see a doctor immediately. All these things are signs of infections or injuries that need to be treated by a doctor.

How Big Is It Supposed To Be?

All right, since I know you're all dying to know this, here we go: average penis size is somewhere in the vicinity of 5-6 inches long when erect. This average is based on several international different surveys done by researchers and doctors. What this means is that five to six inches is the most common penis length, but that there are penises that are longer and penises that are shorter that are all perfectly normal, healthy, desirable penises.

Penis size has nothing to do with body size. Bigger, taller people do not necessarily have bigger or longer penises. Shorter people don't necessarily have smaller ones. The size of your hands, feet, or nose is no indicator. Neither is how big a penis is when it is soft: some penises get a lot bigger when they get hard, other penises don't get all that much bigger when they get hard. Fat people do not have smaller penises than thin people, Asian people do not have smaller penises than White people, and Black people's penises don't average any larger than anyone else's. Those are all stereotypes, and have no basis in truth. Penises come in a lot of different possible sizes. That's nothing more or less than run of the mill human variation.

The growth of your penis during puberty is hard to predict. There is no magic age when puberty starts and stops, and therefore there is no magic age when your penis will start to grow or stop growing. Sometimes they seem to grow all at once, and a change will seem very sudden, and other times, the change will happen slowly. Again, that's just normal human variation. Lots of folks worry that their penis won't be big enough, and that sexual partners won't like it or won't want them as partners because of their penis size. That's really pretty unrealistic.

The penis size issue is a lot like the breast size issue. Breasts, like penises, come in all different shapes and sizes. Some people are attracted to big breasts. Some people are attracted to smaller breasts. Some people like them to be in between. Some people couldn't care less. Some people don't even like breasts at all. Most people find that there is a wide range of breast sizes that can be attractive to them, providing that there are other things about the person they're attached to that are attractive and interesting. Any person who decided to date someone solely because of their breast size would be pretty superficial - and really, it's pretty insulting to date or desire someone just because of a single body part. We're people, not parts.

Same goes for penises. Some people prefer longer penises. Other people prefer shorter ones. Many people like average-sized ones. Some people could honestly not care less whether there's a penis involved in their sex lives or not. And yes, some people don't like penises at all. Most people find that there are other, more important considerations than penis size when they are considering whom they like as a potential lover, spouse or partner. (Just for the record, this is all also true for gay and bisexual people, too, not just for heterosexual people.)

The short answer is that there are a lot of things that are just as or more important than penis size. If you are an interesting, attentive, creative, and responsive person and people enjoy being around you and spending time with you, how big your penis is really won't matter one bit. Honest, it really won't. The qualities that make someone desirable, sexy, or a good lover are the qualities I just listed - not the size or shape of any given body part(s). Big feet don't make you an Olympic runner, big hands don't make you a concert pianist, and a big penis doesn't make you a sexual superstar. Talent, attention, smarts, and a desire to do your personal best are what make all those things happen.

The Family Jewels

Your scrotum is the little bag of skin lined with muscle that hangs below your penis and contains your testes or testicles. The halves of the scrotum are divided by a wall of muscle. Externally you can see a line, called the raphe, that divides down the center of the scrotum. The scrotum's muscles are used to pull the testes closer to the body in order to protect or warm them; when the muscles relax, the testes hang considerably lower and the scrotum may look longer. This is why, when you are cold - say you jump into a cold swimming pool or lake - your scrotum shrivels up so that your testicles are held tightly against your body. Your body is trying to keep your testicles warm! The testes or testicles are the most famous and most visible of the many reproductive glands. The testes are about the size of a large olive, and about the same shape. They're incredibly sensitive to touch and pressure, as any person with testicles who's ever had a groin injury, even a minor one, can tell you.

The testes produce testosterone, the so-called "male" hormone, and they also produce sperm, which are formed in the testes and move into the epididymis to mature. People without penises or testicles have testosterone in their bodies, too, produced mostly by the adrenal glands, an additional source of testosterone in folks with testicles.

The epididymis is a small organ that sits on top of the testicle. It is made up of a little bundle of squiggly tubes and is a "holding pen" for sperm. When you ejaculate, sperm are moved from the epididymis into the vas deferens, the tubes that take sperm up and out of the scrotum area and into other ducts so they can be ejaculated as a part of semen. Sperm that don't get ejaculated live in the epididymis for around four to six weeks before they die and are reabsorbed into the body. It's very similar to the way old blood cells die and are reabsorbed and recycled. This is why it's impossible - even if you never ejaculated in your whole life - to have "excess" sperm build up in your body.

The epididymis and testicle are the two major organs inside the scrotum. They don't just float around in there, though. They are anchored to the body by what is called the spermatic cord. The spermatic cord is a bundle of nerves and blood vessels that serve the testicle and epidydimis, plus the vas deferens, which is a long tube which carries sperm up and out of the scrotum so that it can be ejaculated.


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So, where does the vas deferens go? Well, I'll tell you: it goes up into the body, where it empties into the seminal vesicles. This is the place where sperm get mixed up with some of the other ingredients that make semen. Sperm themselves are only about two to five percent of the volume of the semen that is ejaculated: the rest is other fluids. Those fluids are produced by several different glands: the prostate, the bulbourethral or Cowper's glands, and some fluids produced by the vas deferens and the seminal vesicles themselves, and are added to the semen mixture at various points along the way before the semen is ejaculated.

The bulbourethral glands, also called the Cowper's glands, primarily produce a liquid sort of mucus. It is this fluid that sometimes comes out when someone is really aroused, but before ejaculation. "Pre-ejaculate" or "precum" is a slippery, sometimes slightly sticky fluid that has the ability to neutralize any acid (from urine) that might be inside the urethra. Since sperm do not thrive under acid conditions, pre-ejaculate helps to make the conditions in the urethra favorable for sperm to survive. The same fluid is also a component of semen itself. Because pre-ejaculate has to travel through some ducts that may or may not have sperm lurking in them, it is usually considered fairly likely that there will be live sperm in pre-ejaculatory fluid, though at lower concentrations than in semen. Pre-ejaculate can also carry disease organisms, including the HIV virus.

The prostate gland is a large, chestnut-shaped gland that surrounds a small part of the urethra within the body, below the bladder. It marks the spot where the seminal vesicles empty into the urethra, and is also the point at which fluids from the prostate (approximately 30% of the total volume of semen) get mixed into the semen. The prostate is very sensitive to pressure and touch. Many people enjoy having their prostates stimulated, which is usually done by inserting a lubricated and latex-glove covered finger into the anus - since the prostate is inside the body, this is the only way to reach it, though testicular or perineum massage may more indirectly stimulate the prostate.

After prostate fluid has been added, the semen is now all ready to be ejaculated. It is ejaculated out of the urethra through a series of muscular contractions that begin in the vas deferens and continue all along the path that the sperm and fluid take in order to leave the body.

Urination Information The urinary system is not nearly so complicated as the reproductive system. Basically, urinary anatomy consists of three basic parts: the bladder, the urethral sphincter, and the urethra itself.

The bladder is the muscular pouch or reservoir that holds urine between the time it is filtered out by the kidneys and the time that you expel it from your body by urinating (peeing). It is quite flexible and can expand to hold quite a bit of liquid, though the amount varies from person to person.

The bladder opens out into the urethra through a sort of muscular "gate" called the urinary sphincter. This is a ring of muscle around the opening between the bladder and the urethra that we learn to voluntarily close or open depending on when we want to urinate. When we open it, urine flows out of the bladder. If it is closed, the urine stays in the bladder. The urethra is a long tube that extends from the bladder all the way to the tip of the penis. It is approximately 8 inches long, though it is sometimes shorter or longer. Urethras within the penis are quite a lot longer than the urethras of those with a vulva: the latter are more often only approximately 4 inches long. The urethra ends at the urethral meatus, the opening of the urethra that is at the tip of the penis, in approximately the center of the head or glans.

written 06 Mar 2001 . updated 15 Jun 2014

Information on this site is provided for educational purposes. It is not meant to and cannot substitute for advice or care provided by an in-person medical professional. The information contained herein is not meant to be used to diagnose or treat a health problem or disease, or for prescribing any medication. You should always consult your own healthcare provider if you have a health problem or medical condition.