Erection: how it works
To understand how your body produces an erection it will help to first understand a little about blood flow through the penis in its flaccid (non-erect) state.
Blood supply to the erectile tissue of the penis
The main blood supply into the erectile tissue of the penis is via the 2 deep central arteries (also known as the cavernosal arteries) — one runs down the length of each cigar shaped corpus cavernosum.
The corpora cavernosa make up the bulk of the spongy erectile tissue of the penis. 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. |
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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. |
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| 5. The body then produces an enzyme known as phosphodiesterase 5 (PDE5), which breaks down the erection-causing body chemical cGMP. Blood is redirected back out of your penis and into the rest of the body. |
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| 6. Your penis returns to its previous limp (flaccid) state. |
Last Reviewed: 21 September 2009
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