FirstMed Consulting Blog

The Penis itself is a spongy organ and when relaxed feels soft and smooth, when the penis is in this state it is referred to as being “flaccid”. To understand how an erection takes place we need to understand the structure of the penis, this is shown simply in figure 1 and explained in detail below.

The penis is a tube like structure composed of three cylinders, two of which are paired. These two paired cylinders are called the corpora cavernosa and are responsible mainly for the erectile functioning of the penis. A tough thick membrane covers the penis, so when the penis fills with blood this membrane helps create a firm structure that allows penetration. The third cylinder of the penis is known as the corpus spongiosum. The corpus spongiosum runs centrally through the penis and contains the urethra (duct through which urine is discharged). It is these three sponge like cylinders which fill with blood to produce an erection.

Physiologically an erection takes place when there is an increase in blood flow into the penis and a decrease in flow out of it. This causes the penis to become engorged with blood and enlarge producing an erection. To understand this mechanism fully we must look at the blood supply to the penis. Blood enters the penis via a blood vessel known as the Pudendal artery and leaves via the dorsal vein as shown in figure 2 below:

As Figure 2 illustrates the blood vessels pass through the Corpora Cavernosa. The Corpora Cavernosa is cylindrical in structure and has a sponge like property. When an erection takes place these blood vessels dilate and blood flows into the Corpora Cavernosa via the Pudendal artery. The Corpora Cavernosa acts according to its sponge like properties and “soaks up” this blood. At the same time the outflow of blood from the penis is reduced by compression of the dorsal vein following the increase in pressure within the Corpora Cavernosa. This leads to an overall increase in blood to the penis and results in an erection. The Corpus Spongiosum (the third cylinder in the penis) is less turgid than the Corpora Cavernosa and plays a crucial part in protecting the urethra (mentioned earlier) during erections. During the process of an erection as the blood flow changes the penis goes through three phase or stages. These are Flaccidity, Tumescence and erection. These three stages are shown below in figure 3.