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Last updated February 17, 2020. 2 minute read

How do erections work? It's surprisingly complicated

An erection is a pretty amazing process, requiring several body systems to collaborate simultaneously. It’s not just a sign that you’re ready for sex—it can be an early indicator of larger health issues if it isn’t working properly.

Self Written by Michael Martin
Reviewed by Dr. Mike Bohl, MD, MPH

The penis. If you have one, it couldn’t be more familiar, yet its mechanics can still seem pretty exotic. An erection is a pretty amazing process, requiring several body systems to collaborate simultaneously. It’s not just a sign that you’re ready for sex—it can be an early indicator of larger health issues if it isn’t working properly. Here’s a quick look at how erections work.

Vitals

  • Every erection is the result of a chain reaction that starts in the brain with arousal and ends in the penis.
  • An erect penis can hold up to eight times its normal blood flow.
  • There are several potential causes of erectile dysfunction. It can be an early sign of a larger health condition.
  • If you’re experiencing ED, talk with your healthcare provider.

How do guys get erections?

Erections are surprisingly complicated. Each one takes your heart, lungs, hormones, nerves, blood vessels, and even your mood to work together seamlessly in a complex sequence of events. When everything goes right, an erect penis can contain up to eight times the normal blood flow (Van Driel, 2015). But one missed reaction in that chain can lead to erectile dysfunction.

Anatomy of the penis

The penis consists of the shaft, the head (or glans), and the meatus (or the opening of the urethra). Two tubes called the corpora cavernosa run down the length of the penis—they’re filled with spongy tissue and many tiny blood vessels. So is the corpus spongiosum, which runs down the underside of the penis and houses the urethra.

What is an erection?

An erection is perhaps the most obvious sign of sexual arousal. It’s a physical response to a chemical reaction in the body. During sexual arousal, those tiny blood vessels in the penis dilate. The spongy tissue fills with blood, and an erection occurs. After ejaculation (or a loss of arousal), that blood drains away, and the penis reverts to its flaccid size and appearance.

How do erections work?

Every erection is the result of a relay race that starts in the brain with arousal and ends in the penis with an erection:

  1. Men become aroused (or experience an erection while sleeping or upon waking)
  2. The brain passes that signal to the body through the spinal cord and nerves
  3. cGMP causes the corpora cavernosa to relax, allowing blood to rush into the cavernosal arteries.
  4. While blood rushes into the penis, the veins that drain blood from the penis get compressed, causing the increased blood to be trapped in the penis, causing an erection.
  5. An enzyme called phosphodiesterase-5 breaks down cGMP, causing the penis to return to its flaccid state.

What if you can’t get an erection?

Erectile dysfunction happens when you can’t get or maintain an erection sufficient to have satisfying sexual intercourse. ED can be the first warning sign of more serious medical conditions like diabetes, heart disease, high blood pressure, or low testosterone. If you’re struggling with erectile dysfunction, seek medical advice to find out what might be causing your ED and the treatments that are available. Your sex life—and your overall health—can only benefit.