The corpus cavernosum and corpus spongiosum are the primary erectile tissues forming the structure of the penis. These specialized vascular bodies enable the penis to transition from a flaccid to an erect state, supporting male sexual function. Both structures are composed of a sponge-like network of smooth muscle, connective tissue, and blood vessels. They are designed to rapidly fill with and temporarily trap blood during sexual arousal, though they have distinct, interdependent roles in achieving full erection.
Anatomical Placement and Structure
The two corpora cavernosa are paired cylindrical structures that run parallel to each other along the upper side (dorsum) of the penis, from the pubic bones to near the tip. These two columns are the main structural components responsible for penile rigidity. They are encased together in a dense, protective fibrous layer called the Tunica Albuginea, and the tissue inside is a vast network of irregular, blood-filled spaces known as lacunar spaces or sinusoids, which are lined with endothelial cells.
In contrast, the corpus spongiosum is a single, smaller cylindrical column positioned ventrally, or along the underside, in a groove created by the two corpora cavernosa. The corpus spongiosum completely surrounds the urethra, the channel through which both urine and semen exit the body. The spongiosum extends distally, expanding to form the glans penis.
How the Tissues Differ
The difference between the two tissues lies in their structure and functional roles during an erection. The corpus cavernosum is the main engine of rigidity, accounting for approximately 90% of the blood volume. Its ability to achieve high internal pressure is directly related to its thick, less elastic Tunica Albuginea, which acts like a tough, non-stretching sheath.
The corpus spongiosum is encircled by a significantly thinner and more elastic Tunica Albuginea. This structural difference prevents the spongiosum from becoming as rigid as the cavernosum; its internal pressure reaches only about one-third of the cavernosum’s pressure. This lesser rigidity is a functional necessity, ensuring that the urethra remains open throughout the erection and during ejaculation, preventing compression by the surrounding engorged tissues.
The Physiology of Erection
Erection is initiated by neural signals from the brain and spinal cord, which trigger the release of neurotransmitters like nitric oxide at the nerve endings. This chemical signal causes the smooth muscle in the walls of the arteries and the trabecular tissue within the corpora cavernosa to relax. This relaxation leads to a rapid increase in arterial blood flow into the lacunar spaces, often increasing 20 to 40 times the resting rate.
As the corpora cavernosa fill and expand with blood, they press outward against the surrounding non-compliant Tunica Albuginea. This expansion compresses the small veins, known as subtunical venules, positioned between the erectile tissue and the fibrous sheath. This veno-occlusive mechanism effectively traps the blood inside, preventing outflow. This allows the internal pressure to rise to approximately 100 mmHg, maintaining the rigidity necessary for intercourse.
Factors Affecting Tissue Health
The health of the corpus cavernosum and spongiosum is linked to systemic vascular health, as the erectile process is fundamentally a vascular event. Chronic conditions like diabetes, hypertension, and high cholesterol can damage the endothelial cells lining the blood vessels and lacunar spaces. This damage impairs the smooth muscle relaxation required for proper blood inflow. Smoking and advanced age also contribute to the hardening of the arteries and the development of corporal fibrosis, where smooth muscle is replaced by non-elastic scar tissue.
Fibrosis within the Tunica Albuginea can lead to conditions such as Peyronie’s disease, where localized scar tissue or plaque forms, causing a loss of elasticity. This stiffness can cause a painful curvature or deformity during erection. Plaque formation also compromises the veno-occlusive mechanism, potentially leading to venous leakage and an inability to maintain rigidity, which is a common cause of erectile dysfunction.