Spongy Urethra

Structure/Morphology

The urethral wall consists of three layers, including a mucosal, muscular, and erectile layer. The proximal epithelium is transitional epithelium, while the distal epithelium is stratified squamous.

The male urethra is approximately 20 cm long and divided into four segments (intramural, prostatic, membranous, and spongy).

The urethra has a flattened, star-shaped lumen lined by pseudostratified columnar epithelium. The lumen collapses when not in use, thus forming longitudinal folds. Scattered mucous glands (glands of Littré) extend from the surface epithelium a short way into the lamina propria.

In a flaccid penis, the spongy urethra is approximately 15 cm long and extends from the membranous urethra to the external urethral orifice. The proximal part of the spongy urethra is termed the bulbar urethra since the bulbourethral glands open into the urethra here. The distal part of the spongy urethra curves downwards and is termed the penile urethra. The penile urethra dilates at its terminal portion within the glans penis as the navicular fossa.

Anatomical Relations

The spongy urethra lies within the corpus spongiosum of the penis.

Function

The spongy urethra provides passage for urine and semen out of the body by way of the male external urethral orifice.

Arterial Supply

The urethral artery, a branch of the internal pudendal artery, supplies the spongy urethra and surrounding erectile tissue. Circumflex branches of the dorsal artery of the penis also supply the spongy urethra.

Venous Drainage

The venous drainage of the spongy urethral is mainly through dorsal veins of the penis (via the circumflex veins) and internal pudendal veins, which drain into the prostatic plexus. The ventral aspect of the urethra is drained by the urethral veins, which form the bulbourethral veins and eventually terminate in the internal pudendal vein (Quartey, 2006).

Innervation

Autonomic fibers arrive at the spongy urethra by way of the prostatic plexus, an inferior extension of the inferior hypogastric plexus. Lumbar splanchnic nerves supply sympathetic innervation, whereas the pelvic splanchnic nerves supply parasympathetic innervation to the spongy urethra. Somatic innervation is supplied by dorsal nerve of the penis, a branch of the pudendal nerve (Standring, 2020).

Lymphatic Drainage

Lymphatic drainage of the spongy urethra drains mainly into the deep inguinal and external iliac lymph nodes.

List of Clinical Correlates

—Kidney stones

—Hypospadias

—Urethritis

—Catheterization

References

Quartey, J. K. M. (2006) 'Anatomy and Blood Supply of the Urethra and Penis', in Schreiter, F. and Jordan, G.H. (eds.) Urethral Reconstructive Surgery. Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 11-17.

Standring, S. (2020) Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd edn.: Elsevier Health Sciences.