Understanding an Erection
The penis is made up of spongy tissue that holds blood. When the penis is flaccid (soft), blood flows in and out of the tissue. During sexual excitement, extra blood flows into the tissue. The extra blood makes the tissue swell so the penis becomes erect (rigid) and firm enough for intercourse.
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| A Flaccid Penis |
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| A Normally Erect Penis |
When There’s a Problem
Physical or psychological problems can keep the penile tissue from filling with extra blood or from holding the extra blood in. When this happens, the penis remains soft or gets hard but won’t stay hard. This is known as erectile dysfunction.
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Publication Source:
Lue TF, Campbell-Walsh Urology, 9th ed., Chapter 21 – Physiology of Penile Erection and Pathophysiology of Erectile Dysfunction, 2007, pp 723-724
Online Editor:
Rademaekers, Ed
Online Medical Reviewer:
Gomella, Leonard MD
Date Last Reviewed:
1/15/2007
Date Last Modified:
7/9/2002