Physiology of Tumescence and Detumescence
The flaccid penis is restrained by the tonic contraction of the vascular smooth muscle in the cavernosal ar-terioles and sinusoids under the influence of nora-drenergic sympathetic neurons, allowing only a small amount of blood (1-4mL/100g tissue) to enter the penis. Penile erection is produced by the relaxation of these vessels combined with restriction of venous return, both of which result in engorgement of the sinusoids. It requires intact arterial blood flow via the iliac, femoral, pudendal, cavernosal and helicene arteries. The cavernosal smooth muscle surrounds a complex vascular network consisting of endothelial cell lined sinuses, or lacunae, and the helicene arteries. The corpora are enclosed by a dense non-distensible fibrous sheath, the tunica albuginea, and communicate with each other via a medial septum. Subtunical vessels pierce this sheath, coalescing to form the emissary veins, which provide the venous drainage of the corpora into the dorsal vein (Figure 7.2).
The autonomic innervation of the penis is (Figure 7.3) mainly from the thoracolumbar sympathetic (T12-L2) and parasympathetic sacral spinal cord segments (S2-S4), while sensory innervation is via the pudendal nerve (S2-S4). In the proper androgenic
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