How an Erection Occurs
Penis, the male organ of copulation, is located partially outside the body and partially inside. Anatomically speaking it consists of two parts, one in continuation of the other: the body on the outside, and the root on the inside. When it is flaccid, the body section of the penis has a shape approximately round, while erect is more like a triangle with rounded corners.
The root of the penis is made of a spongy body tissue called the corpora spongiosa. This tissue contains many blood vessels and cavities and it extends along the penis to the tip, where it dilates to form glans of penis or head. The urethra passes through the center of the body and it is common channel for urine and semen. Urethra ends with a narrow opening at the top of the glans. Over the spongy body, by both sides, are two long cylinders of erectile tissue called corpora cavernosa. They have a continuous path through the body of the penis and end immediately before the glans.
The corpora cavernosa are called erectile tissue because during sexual arousal, they are expanded by the blood that fills the internal cavities. Blood is temporarily locked inside the corpora cavernosa by contraction of blood vessels that normally ensure its disposal. As a result an increased pressure occurs; the penis expands and hardens which resulting in an erection. The spongy body is also considered an erectile tissue. However, during erection, spongy body does not increase as much as the corpora cavernosa and in addition, it has a normal blood circulation throughout the erection.
Getting an erection is due to a sequence of events that take place in a relatively short period of time. An erection begins with a substantial acceleration of blood flow performed by the nervous system. Many sexual stimuli are processed by the brain and transmitted to the penis through the nerve fibers. As we mentioned above, the penis is made of a network erectile tissue with empty spaces and fine sponge-like tissue. When the penis is flaccid, interior space has a minimum volume and the tissue is condensed. During erection blood fills these empty spaces causing the lifting and expansion of the penis. The amount of blood entering the penis can be increased by physical or physiological stimulation.
As blood enters the penis, there is a decrease in the amount of blood that comes out. The arteries that bring blood dilate; even this led to a general increase of the volume. Veins that ensure blood disposal from the penis are provided with special valves which make the blood that comes out to be reduced gradually. In this way the blood is essentially “closed” temporarily inside the body of the penis, and all these physiological mechanisms are finally materialized in achieving an erection.