Key Concepts
Overview & Anatomy
The penis serves as the organ of copulation and urinary excretion. It consists of three cylinders of erectile tissue: two corpora cavernosa (paired, dorsolateral) and one corpus spongiosum (ventral, surrounds urethra, forms glans at distal end). The glans is covered by the prepuce (foreskin) in uncircumcised men. Mechanism of erection: - Parasympathetic stimulation (pelvic splanchnic nerves, S2โS4): releases nitric oxide (NO) โ smooth muscle relaxation in helicine arteries โ increased blood flow โ fills lacunar spaces in corpora cavernosa โ compression of emissary veins โ erection - Ejaculation: sympathetic stimulation (hypogastric nerve, T10โL2) โ smooth muscle contraction โ emission + ejaculation Clinical conditions: - Phimosis: foreskin cannot be retracted; can cause pain during intercourse; treatment: topical steroid or circumcision - Paraphimosis (emergency): foreskin retracted and cannot return to normal position โ constricting ring โ penile ischemia; manual reduction or emergency incision - Priapism (emergency): sustained, painful erection >4 hours unrelated to sexual stimulation; ischemic (most common, low-flow, high risk) vs non-ischemic (high-flow, arterial); causes: sickle cell disease, medications (trazodone, antipsychotics, PDE5 inhibitors), spinal cord injury - Treatment: aspiration of corpora...