The corpus cavernosum and corpus spongiosum are three cylindrical columns of specialized erectile tissue that form the primary structure of the penis. These tissues are composed of a network of vascular spaces, smooth muscle, and connective tissue, which collectively facilitate the physical changes associated with an erection.
Anatomy of the Erectile Tissues
The penis contains two distinct types of erectile tissue. The corpus cavernosum consists of two paired columns on the dorsal (upper) aspect of the penis. These columns extend from the pubic bone to the glans penis, forming the bulk of the penile shaft. Within the corpus cavernosum, the tissue has a spongy, cavernous structure, characterized by numerous vascular spaces known as sinusoids. These spaces are lined with endothelial cells and surrounded by a meshwork of smooth muscle and fibrous connective tissue.
Located beneath the corpus cavernosum, on the ventral (lower) side of the penis, is the single column of corpus spongiosum. This tissue column encases the urethra, the tube through which urine and semen exit the body. The corpus spongiosum expands distally, forming the glans penis, the cone-shaped tip of the penis.
The Mechanics of an Erection
An erection begins with sexual stimulation, which triggers neural signals from the brain and spinal cord to the penis. These signals lead to the release of neurotransmitters, such as nitric oxide, from nerve endings within the penile tissue. Nitric oxide causes smooth muscle cells lining the arteries and the walls of the sinusoids in the corpus cavernosum to relax, leading to a widening of the arteries supplying blood to the penis.
As these arteries dilate, a rapid influx of arterial blood fills the cavernous spaces within the corpus cavernosum. The increasing blood volume causes the corpus cavernosum to expand, becoming engorged and firm. As it expands, it compresses the venules, the small veins located against the rigid outer layer of connective tissue called the tunica albuginea. This compression traps the blood within the erectile tissue, maintaining penile rigidity.
The corpus spongiosum also fills with blood and becomes firm, but it does not achieve the same degree of rigidity as the corpus cavernosum. This differential firmness prevents the compression of the urethra, ensuring the passageway remains open for ejaculation.
Conditions Affecting Penile Tissues
Various conditions can affect the health and function of the corpus cavernosum and corpus spongiosum. Erectile dysfunction (ED) is a common condition where a person has persistent difficulty achieving or maintaining an erection firm enough for satisfactory sexual activity. This often involves issues with blood flow into the corpus cavernosum, where the arteries may not dilate sufficiently or the venous outflow mechanism may not adequately trap blood.
Peyronie’s disease is another condition impacting these tissues, characterized by the development of fibrous scar tissue, or plaque, within the tunica albuginea. The scar tissue can cause the penis to bend or curve during an erection, sometimes leading to pain or making intercourse difficult.