THE MECHANISM OF BLOOD OUTFLOW FROM THE CAVERNOUS TISSUE OF HUMAN PENIS BY COMPUTER GRAPHICS

Abstract

There are two theories concerning the mechanisms of human penile erection and its maintenance. One theory goes that the artery responsible for blood inflow into the cavernous space relaxes, while the vein responsible for blood outflow actively contracts. The other theory asserts that no active closing mechanism in present in the penile venous system, but rather the erection is totally controlled by the amount of blood inflow. In order to corroborate the vascular construction of the penis, we prepared serial sections of the penis specimens obtained at autopsy and observed these sections by light microscopy, and we investigated the construction of veins which let blood flow out from the corpus cavernosum penis by computer graphics.
As a result, we were unable to find any valves in the blood outflow system. Moreover, efferent vessels were seen to let blood flow from the cavernous spaces, after running immediately below the tunica albuginea for a small distance, to the tunica albuginea, running obliquely through inner veins toward the outside of the tunica albuginea in the direction of the long axis of the penis; then these veins are continuous to the veins on the tunica albuginea.
From the above-mentioned structures we can infer the following mechanism of penile erection. When blood flows into the corpus cavernosum penis at a flow rate greater than usual, the volume of the corpus cavernosum penis increases, the veins running immediately below the tunica albuginea are compressed between the cavernous space and the tunica albuginea, the tunica albuginea extends, and the veins running inside the tunica albuginea are compressed, causing a disturbance in blood outflow and resulting in erection. When the inflow of arterial blood decreases to less than the maintenance rate, the volume of the corpus cavernosum penis decreases, the extension of the tunica albuginea is reduced, and the outflow of venous blood increases, resulting in the termination of penile erection.
From the above, we speculate that the arterial system plays a main role, and the venous system a secondary role, in controlling the human penile erection.