Physical sexual arousal occurs when vascular blood rushes to certain erogenous zones in the body which have erectile tissues. It can happen through mental or physical stimuli, and sometimes it even happens for no reason at all (especially during puberty).
This is called vasocongestion. Vascongestion causes erectile tissues in the genitals to harden, not only making them feel much more sensitive, but also leading to that characteristic hardness. If left unresolved, vasocongestion can cause blue balls for people who have testicles, but it can also cause a pelvic heaviness similar to menstrual cramps for people with vaginas.
Different types of bodies have different types of erectile tissues, particularly in the genitals.
The penis is probably the best-known erectile tissue in the human body. There are three tissues in the penis that become erect when engorged with blood.
The first two are called the corpus cavernosa. These are in a pair along the outside of the shaft of the penis
The third is called the corpus spongiosum. This tissue does not get hard in the same way as the corpus cavernosa. It’s job is to prevent the urethra from being closed off due to such strong swelling, so it sort of forms a protective barrier around the urethra. If the urethra were closed, this would lead to a conflict of interests– the urethra’s job during sex is to carry semen out of the body. If it were closed, ejaculation would not be possible.
The corpus spongiosum also runs down the length of the shaft, but it is also what the glans, or the head of the penis is made of. Unlike the corpus cavernosa, it is all connected as one single muscle.
Damage to either one of these tissues is a prominent reason for erectile dysfunction, usually from injury to the penis such as from jelqing. In particular, priapism, a condition where the penis is erect for an unnaturally long time, can damage the corpus spongiosum. Toxic ingredients, like phthalates, can also cause these injuries.
If you have trouble maintaining hardness, it could be because your erectile tissues cannot keep the blood in. Many doctors will recommend using a toy, such as a penis pump, or an erection ring, to solve the issue.
But it isn’t just penises that have erectile tissues. The clitoris also contains corpus cavernosa, causing the clitoris to become stiff during arousal. Obviously it does not swell up to quite the size of the penis, but the increased blood flow makes the area more sensitive. And for an organ that is full of nerves, that sensitivity can be very strong.
The clitoris does not have a corpus spongiosum because the urethra is unaffected by sexual arousal.
Beyond the genitals, erectile tissue also exists in the perineum (the taint) and the urethra, as well as the ears and nose.
Oddly enough, nipples do not have erectile tissues. Instead, they have smooth muscle that hardens as a response from the automatic nervous system. If someone’s nipples are hard, it does not always mean that they are aroused.
There are other types of vascongestion in areas of the body that don’t have erectile tissues as well. Blushing, allergic reactions, menstruation, REM sleep, and even hemorrhoids are types of vasocongestion.
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