corpus cavernosum

The corpora cavernosa are two parallel columns of erectile tissue running along the dorsal aspect of the penis, situated above the single corpus spongiosum which surrounds the urethra. Each corpus cavernosum is composed of trabeculated smooth muscle and endothelium-lined vascular sinusoids supplied by the cavernosal arteries (branches of the internal pudendal artery). During sexual arousal, parasympathetic stimulation (via pelvic splanchnic nerves, S2-S4) releases nitric oxide (NO), which activates guanylate cyclase, increasing cGMP levels in smooth muscle cells. This causes smooth muscle relaxation, arterial dilation, and filling of the sinusoidal spaces, compressing the subtunical venules against the rigid tunica albuginea and restricting venous outflow (veno-occlusive mechanism)—resulting in erection (tumescence). Detumescence occurs when sympathetic stimulation causes smooth muscle contraction and PDE-5 breaks down cGMP.

Clinical relevance: PDE-5 inhibitors (sildenafil, tadalafil) work by preventing cGMP degradation, prolonging smooth muscle relaxation and enhancing erections—first-line treatment for erectile dysfunction. Priapism (prolonged, painful erection >4 hours) results from dysfunction of this veno-occlusive mechanism, often seen in sickle cell disease, trazodone use, or intracavernosal injections for ED. Peyronie's disease involves fibrous plaque formation in the tunica albuginea causing penile curvature. Understanding the vascular and neural control of the corpus cavernosum is essential for understanding erectile physiology, pharmacologic treatments, and related pathologies tested on USMLE Step 1 (physiology/pharmacology) and Step 2 (clinical management of ED and priapism).