To understand how the male body produces an erection it will help to first understand a little about blood flow through the penis.

Blood supply to the erectile tissue of the penis

cross-section through flaccid (soft) penis

The 2 cigar-shaped corpora cavernosa run the length of the penis and make up the bulk of the spongy erectile tissue of the penis. During an erection, these fill with blood.

The blood flows into the erectile tissue mainly via 2 deep central arteries (also known as the cavernosal arteries) — one runs down the length of each corpus cavernosum.

Blood flows out of the erectile tissue through the drainage system of open veins around the outside wall of the corpus cavernosum.

How an erection is produced

1. You become sexually stimulated by a thought or action.
your brain is sexually stimulated
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2. Your body releases a chemical known as nitric oxide, which is known to dilate blood vessels.
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3. The nitric oxide triggers the action of guanylate cyclase, an enzyme that helps activate an erection. It works by prompting the release of a body chemical called cyclic guanosine monophosphate (cGMP). This causes the smooth muscle cells in the penis’ erectile tissue to relax.
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4. When the smooth muscle cells relax they allow the central artery and other incoming blood vessels to widen as well as the mesh of spongy erectile tissue. This allows more blood to flow via the central artery into the spongy erectile tissue of the penis.

As the 2 cigar-shaped corpora cavernosa fill with blood, the spongy tissue presses up against the veins in the outside walls of the corpora cavernosa, compressing them and stopping the blood from flowing back out of the penis. With more blood flowing in and less flowing out, the penis becomes erect.

cross-section through erect penis
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5. The body produces an enzyme known as phosphodiesterase 5 (PDE5). After a signal, such as orgasm or interruption, PDE5 breaks down the erection-causing body chemical cGMP and blood is redirected back out of the penis and into the rest of the body.
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6. Your penis returns to its previous limp (flaccid) state.

Last Reviewed: 01/12/2015

myDr


References

1. Tracey DJ, Baume P. Anatomica: The Complete Reference to the Human Body and How it Works. Random House Australia, 2000. 2. Andrology Australia. How an erection works: the details (17 Aug 2015). https://www.andrologyaustralia.org/2015/08/how-an-erection-works/ (accessed Nov 2015).