Erection

An erection is the enlargement and stiffening of erectile tissue, usually in the penis, when blood fills its vascular spaces and outflow is restricted.

Penile erection: The enlargement and stiffening of the penis as erectile tissue fills with blood. This is the usual form of erection, produced by coordinated changes in penile blood flow.
Erectile tissue: Specialized vascular tissue that can engorge with blood and become enlarged or firm. Erection is the characteristic change in this tissue.
Erectile dysfunction: Persistent difficulty achieving or maintaining an erection sufficient for sexual activity. It is the clinical condition defined by impaired erection.
Detumescence: The return of erectile tissue to its non-engorged, flaccid state. It reverses erection as blood inflow falls and venous outflow resumes.
Corpus cavernosum: One of two cylindrical erectile bodies in the penis that fill with blood during erection. Its expanding spaces provide most penile rigidity.
Penis: An external genital organ containing the urethra and erectile tissues. Its paired corpora cavernosa and corpus spongiosum are the main sites of penile erection.
Phosphodiesterase type 5 inhibitor: A drug that blocks the enzyme PDE5, prolonging cyclic GMP signaling in smooth muscle. These medicines can support erection by sustaining the nitric-oxide pathway's vascular effects.
Sexual arousal: A state of sexual interest or physiological responsiveness to sexual stimuli. Arousal can trigger erection, but the two are distinct and do not always coincide.
Corpus spongiosum: The erectile tissue surrounding the male urethra and forming the glans penis. It engorges during erection while remaining less rigid, helping keep the urethra open.
Endothelium: The thin layer of cells lining blood vessels and the heart. Endothelial signaling helps regulate the vessel relaxation needed for increased penile blood flow.

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