Penis - structure (draw cross-section), vascular and nerve supply, mechanism of errection

Penis - Structure, Vascular and Nerve Supply, Mechanism of Erection

Introduction-

The penis is the male copulatory organ that serves reproductive and urinary functions. It consists of erectile tissues, a vascular network, and specialized nerves, enabling its role in sexual intercourse and urination.

Structure

Macroscopic Features:

1. Regions:
   • Root: Fixed portion attached to the perineum.
   • Body (Shaft): Free portion consisting of erectile tissues.
   • Glans Penis: Expanded distal portion, covered by the prepuce in uncircumcised males.
2. Erectile Tissues:
   • Corpora Cavernosa (2):
     • Paired cylindrical structures positioned dorsally.
     • Surrounded by a dense tunica albuginea.
   • Corpus Spongiosum (1):
     • Single midline structure ventrally placed.
     • Contains the spongy (penile) urethra.
     • Expands distally to form the glans penis.
3. Coverings:
   • Skin, subcutaneous tissue, and Buck's fascia (deep fascia of the penis).

Cross-Sectional View:

• Central positioning of the corpus spongiosum enclosing the urethra.
• Dorsal positioning of the paired corpora cavernosa.
• Surrounding fascial layers (Buck’s fascia and tunica albuginea).
• Superficial dorsal vein, dorsal arteries, and dorsal nerves.

Vascular Supply

arterial supply

Arterial Supply:

1. Internal Pudendal Artery: Main source, branching into:
   • Deep Arteries of the Penis: Supply the corpora cavernosa.
   • Dorsal Arteries of the Penis: Run along the dorsal surface.
   • Bulbourethral Arteries: Supply the corpus spongiosum and bulb of the penis.

Venous Drainage:

1. Superficial Dorsal Vein: Drains into the external pudendal veins.
2. Deep Dorsal Vein: Drains into the prostatic venous plexus.

venous supply

Nerve Supply

1. Somatic Innervation:
   • Dorsal Nerve of the Penis: Branch of the pudendal nerve; provides sensory innervation.
2. Autonomic Innervation:
   • Sympathetic Fibers: From the hypogastric plexus; involved in detumescence.
   • Parasympathetic Fibers: From the pelvic splanchnic nerves (S2-S4); responsible for erection.

Mechanism of Erection

1. Initiation:
   • Triggered by sensory or psychological stimuli.
   • Parasympathetic activation releases nitric oxide (NO).
2. Hemodynamic Changes:
   • Arterial Dilation: NO induces relaxation of smooth muscle in the deep arteries, increasing blood flow into the corpora cavernosa.
   • Venous Compression: Expansion of the erectile tissues compresses subtunical venules against the tunica albuginea, trapping blood within the penis.
3. Maintenance:
   • Sustained arterial inflow and venous occlusion maintain rigidity.
4. Detumescence:
   • Sympathetic activation causes contraction of smooth muscle, reducing arterial inflow and facilitating venous outflow.

Sources

1. Gray’s Anatomy for Students, 4th Edition.
2. Sobotta Atlas of Human Anatomy, 16th Edition.