Men’s Erectile Function

Understanding the basics of the penis and how it works is an important step in…
Read below to learn about the male sexual anatomy and how erections happen.


The Male Penis

A male penis is made up of 4 basic structures:

  • The soft, hairless outside skin that stretches over the penis.
  • The urethra, a central inside tube where urine and occasionally semen passes out from the body.
  • The spongy paraurethral gland that wraps around the urethra from the bladder to the tip of the penis head (aka corpus spongiosum). This gland secrets drops of fluid into the urethra to keep it lubricated and open. Paraurethral tissue also makes up the head of the penis, giving it a soft, spongy feel. The paraurethra does not change size or texture in response to sexual arousal.
  • The clitoris is the hydraulic, erectile part of the penis, and is also known as the corpora (body) cavernosa (caverns). Just like in women, the male clitoris is shaped like a wishbone, connected at the tip and separating into two legs/shafts inside the body.

Because of higher testosterone levels, the male clitoris is longer (about 5”) than the female clitoris (about 4”), and develops primarily on the outside of the body. Also, one cannot directly touch a male clitoris as you can a woman’s.

The genital blood supply (pudendal artery) and nerve connection (pudendal nerve and parasympathetic nitrergic nerves) are the same in all genders. No bone structure exists within the male penis in humans.

The Hydraulics of an Erection

The clitoral structure is composed of a fibrous, slightly flexible outer layer (tunica) which surrounds multiple inner balloon-like caverns. Blood moves in and out of the caverns, filling them like balloons and naturally flooding them several times per day to provide routine oxygen and nourishment. These floods are the morning erections men notice in the morning and during the day unrelated to sexual arousal. When the caverns are empty, the clitoris is very flexible and floppy like a partly-filled balloon.

What Causes an Erection?

Sexual arousal is a response to stimulation produced by several mind and body systems working together. An erection is one sign of a man’s sexual arousal, when the clitoral body swells with blood and the penis becomes stiff and hard.

Functionally, there are two main principles to consider: getting blood to flow into the clitoris to stiffen the penis, then keeping blood in.

Pumping blood into the clitoris

Erections require several different functioning systems to work together; the most important being nerves & blood vessels.

The nerves of sexual arousal produce nitric oxide to cause special arteries in the clitoris to relax and open up, allowing blood to flood in. Nitric oxide can also be released by rubbing and massaging the blood vessels themselves, which is why vibrators increase engorgement.

When nitric oxide opens the floodgates, the pressure of the blood in the caverns presses hard against the tunica, and the whole structure stiffens up. High arousal pushes quite a bit of blood into the clitoris, such that the outflow veins are squashed, effectively trapping the blood inside.

During the development of an erection, the other structures of the penis ‘tag along’, but do not contribute at all to the erection. The skin on the outside of the penis stretches tight, while the urethra and paraurethra conform to the new, erect shape. The tip of the penis does not change shape because the clitoris is not in the tip. Overall, the penis changes shape mostly in the wideness/girth, and to a lesser extent in length. It looks much longer because the penis is more obvious when it sticks out away from the body.

Keeping blood in the clitoris

Normally, blood drains out of the clitoris through veins on the very outside of the tunica. Flexibility of the clitoris’ tunica is one key to holding blood into an intact clitoris. To hold erections, the tunica:

  • must be complete, without tears or holes
  • stretch flexibly, and press the outflow veins shut almost completely
  • isn’t scarred from trauma or inflammation, leaving it too small to stop the flow.

The other key is continued arousal. If erotic stimulation stops or non-erotic thoughts interfere, the erection will go away.

What if you lose your erection?

Erections are important for penetration, but they are not necessary for sexual pleasure or orgasm. The sensory nerves that trigger pleasure and orgasm often function even when the clitoral structure won’t hold erections sufficient for penetration. Consider that women’s clitori swell and ebb with different levels of stimulation and arousal, yet experience sexual pleasure and orgasm routinely. This happens because the female tunica covering the clitoris is relatively thin and porous compared to the male tunica.

The male tunica is much thicker. This thickness allows it to both swell and press on the outflow veins to close them off. Thus, with sufficient pressure, men hold erections for a longer period of time than women do. This is what supports penetrative sex play, but men can enjoy arousal and orgasm without erections. If you are experiencing difficulty getting and maintaining an erection, see our article about erectile dysfunction to learn about causes and treatment approaches.

Penis Questions Answered

Here are some answers to your penile questions:

Q: Is there a bone, or not?
A: No, there is no bone in a human penis. All erectile stiffness is from blood pressure inside of the clitoris itself.

Q: Why are penises erect in the mornings?
A: Penises are puffed up in the morning because the body is naturally oxygenating them, and will do so about 4 times per day. This is one of the activities that men with nerve damage notice: they don’t get their usual morning erections because the neural control is damaged. If this has happened, then the man needs to use a vacuum pump 3x daily (just to puff the blood in), so that the clitoris stays functional and doesn’t scar. (For more information, see Penile Rehabilitation.)

Q: Why do they shrink up in cold water or cold weather?
A: Penises shrink in cold weather/water because the body naturally pulls blood into the core of the body to keep warm. Less blood to the penis means that the size will shrink temporarily.

Q: Why do penises float in bath water?
A: Non-erect penises float in bath water because there is more glandular tissue (paraurethra) and air (inside the urethra) than blood in the clitoris. If a man gets an erection, the blood in the clitoris will weigh the penis down, even as it becomes stiffer.

Q: How can you aim your pee when you have an erection?
A: If a healthy penis is fully engorged, a man can’t pee so “aim” is irrelevant. The muscles at the base of the bladder (above the prostate gland) are neurologically designed to hold tight during erections, to allow the alternate semen pathway to take over and permit ejaculation. The man may feel that his bladder is very full, but until he allows the erection to slowly subside, he won’t be able to empty his bladder until the nerves of sexual arousal switch the muscle back off and allow urination.

Men with nerve damage from diabetes, surgery, trauma, etc. sometimes do have problems with urine leakage because the nerve doesn’t function correctly and hold the muscle tight. Each situation is unique, though, and some men recover full bladder holding over time.

Q: How does a cock ring work?
A: A cock ring works by trapping blood in the clitoris. By trapping the outflow veins ever so lightly, we can support an erection by not allowing the clitoris to deflate–similar to a light tourniquet on an arm. We only sell easily removable or adjustable cock rings, because keeping blood trapped for a long period of time can permanently damage the inside lining of the clitoris by depriving it of oxygen. Have a steel-hard erection, but don’t wear steel cock rings.

Q: What techniques can help maintain erections?
A: Any technique or device that wraps around a penis shaft will help hold erections. Rubber bands (watch the pubic hair), cock rings, hands (particularly grabbing at the base and stroking out from the body) helps trap blood in the clitoris. Stimulation of the clitoral nerves with the hands rubbing along the shaft is an added bonus. Just don’t hold on too tightly for too long.

Vacuum pumps help the inflow of clitoral blood dramatically by mechanically stretching the clitoral tunica larger. If blood can flow in, the vacuum pump is making room for it to flow in.

Vibrators activate the neural mechanism that begins blood flow into the penis. Even if the nerves responsible for sexual arousal have been damaged, if the clitoral structure is still functional, you’re still a go. Vibrators cause sheer stress, and sheer stress applied to the inner blood vessels of the clitoris activate blood flow. Therefore, vibrators are a non-drug method for bringing blood into the clitoris.

Viagra (the drug sildenafil) works by keeping nitric oxide working in the clitoris. It does not cause erections, but it allows them to stay once they’ve been started by either erotic thought or manual stimulation.

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