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A corpus cavernosum is one of a pair of a sponge-like regions of erectile tissue which contain most of the blood in the male penis during erection. There are corresponding structures and functions in the female clitoris. The term literally means "cave-like body" (plural: corpora cavernosa).
Male anatomy
Three expandable cylindrical formations along the length of the penis hold blood during erection. The two corpora cavernosa lie along the penis shaft, from the pubic bones to the head of the penis, where they join. These formations are made of a sponge-like tissue containing irregular blood-filled spaces lined by endothelium and separated by connective tissue septa. There is one smaller such region (the corpus spongiosum) along the bottom of the penis, which contains the urethra.
In some circumstances, release of nitric oxide precedes relaxation of muscles in the corpora cavernosa and corpus spongiosum. The spongy tissue fills with blood, from arteries down the length of the penis. A little blood enters the corpus spongiosum; the remainder engorges the corpora cavernosa, which expand to hold 90% of the blood involved in an erection, increasing both in length and in diameter.
Blood can leave the erectile tissue only through a drainage system of veins around the outside wall of the corpus cavernosum. The expanding spongy tissue presses against a surrounding dense tissue (tunica albuginea) constricting these veins, preventing blood from leaving. The penis becomes rigid as a result. The glans penis, the expanded cap of the corpus spongiosum, remains more malleable during erection because its tunica albuginea is much thinner than elsewhere in the penis.
Female anatomy
The clitoris is the female equivalent of the male penis. The body of the clitoris contains erectile tissue in a pair of corpora cavernosa with a recognisably similar structure.
In some circumstances, release of nitric oxide precedes relaxation of the clitoral cavernosal artery and nearby muscle, in a process similar to male arousal. More blood flows in through the clitoral cavernosal artery, the pressure in the clitoral corpora cavernosa rises, and the clitoris is engorged with blood. This leads to extrusion of the glans clitoris and enhanced sensitivity to physical contact.
The female anatomy has no corpus spongiosum, but instead two vestibular bulbs beneath the skin of the labia minora (at the entrance to the vagina), which expand at the same time as the glans clitoris to cap the ends of the corpora cavernosa.
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