What is it about?
This text is a comprehensive medical update on the structure and function of the human penis, presented in the Encyclopedia of Reproduction. It details the "fibrovascular assembly" of the penis, describing it as a hydraulic system composed of three cylinders: two paired corpora cavernosa (responsible for rigidity) and one corpus spongiosum (which houses the urethra). It explains that the penis does not have a bone (os penis) like many other mammals, but instead relies on a "fibroskeleton"—specifically a bi-layered tunica albuginea and a "distal ligament" in the glans—to maintain shape and rigidity during erection. Additionally, the text redefines the penile venous system, identifying seven specific erection-related veins (rather than the traditionally taught single deep dorsal vein) that must be compressed to maintain an erection.
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Why is it important?
Correcting Anatomical Myths: It updates centuries-old anatomical knowledge, identifying the penis as the last independent compartment of the human cardiovascular system to be fully understood. Improving Surgical Outcomes: Understanding the true number and location of erection-related veins (one deep dorsal, two cavernosal, and four para-arterial veins) is critical for surgeries treating venous leakage, a common cause of erectile dysfunction. Treating Dysfunction: It provides the structural basis for diagnosing and treating conditions like Peyronie’s disease (curvature), congenital defects like hypospadias, and priapism. Restoring Potency: It establishes that rigid erection is a mechanical phenomenon dependent on specific structures (like the outer tunica layer), which guides reconstruction strategies for patients with impotence.
Perspectives
The "Bi-Layered" Perspective: Unlike traditional teachings of a uniform layer, the tunica albuginea is actually composed of two distinct layers: a 360-degree inner circular layer and an incomplete 300-degree outer longitudinal layer. The outer layer acts as a continuation of skeletal muscles and is the key determinant for erectile rigidity. The Evolutionary Perspective: Humans lack a penile bone, unlike dogs or rats. Instead, humans evolved a specialized "distal ligament" (an os penis analog) and a hydraulic system that follows Pascal's law, where fluid pressure is transmitted equally to create rigidity. The Hemodynamic Perspective: A rigid erection requires a seamless interplay where arterial inflow increases, and venous outflow is physically blocked by the expanding sinusoids compressing the veins against the tunica albuginea.
Professor Geng-Long Hsu
Microsurgical Potency Reconstruction and Research Center, Hsu’s Andrology
Read the Original
This page is a summary of: Penis Structure—Erection, January 2025, Elsevier,
DOI: 10.1016/b978-0-443-21477-6.00349-7.
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