Despite its simple appearance, the penis is one of the most complex parts of the human body. Most people believe that because they understand the two main functions of the penis, they know everything about its structure too. The fact is, however, that there are actually plenty of things that very few people know about the
penis – with this in mind, we are providing a comprehensive general guide to the penis.
In essence, there are two parts making up the human penis: The shaft and the glans, which is also known as the head.
The shaft is not a muscle, it is actually made up of three columns of tissue that form its shape. The two that make up the top of the penis are called the corpora cavernosa, and the one underneath them is known as the corpus spongiosis. During an erection, the blood vessels supplying the penis dilate and allow more blood to reach the penis. The three corpora are filled up with blood, and stiffer tissues that surround the corpus cavernosal constrict the veins that would normally allow blood to drain from the penis. This combination of actions and procedures cause the penis to become stiff. Unlike many other mammals that have a bone in the penis to support the erection, in humans, it is just these three areas of tissue and the pressure of the blood within them that keep the penis stiff.