This post is twitterde porno izlemekpart of Mashable'sMasturbation Week. May is National Masturbation Month, so we're celebrating by exploring the many facets of self-love.

Cast your mind back to the last time you cracked one out, knocked one off, rubbed one out, masturbated — whatever you call it. You may well have noticed a few rather curious physiological responses that occurred in addition to your own personal pleasure party.

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Things like getting a rash across your chest after you come, one of your testes ascending while you're jacking off, or not being able to pee afterwards. Granted, we're often far too preoccupied with our own arousal to pay heed to a lot of these little biological quirks. But, have you ever wondered why they happen?

Mashable spoke to scientists, medical doctors, clinical sexologists, and sex educators to get to the bottom of what your body's getting up to while you're pleasuring yourself.

Why can't you pee immediately afterwards?

After you're done masturbating, it's often nigh-on impossible to urinate, even if nature's call feels really quite urgent. So, what's up? Dr. Myrtle Wilhite — a physician specialising in sexual health — says this is something that affects people with penises and vaginas because the "same neural arousal system" controls the bladder and "moderates the process of sexual arousal." While that might sound quite technical, it basically just means that until you're over your sexual arousal, you won't be able to pee. "The simple answer is that sexual arousal prevents urination," says Wilhite. "Until the arousal subsides neurologically, urination can’t happen."

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Fancy getting into the nitty gritty? OK, good. According to Dr. Jennifer Swann, professor of Biological Sciences at Lehigh University, orgasm is controlled by both the parasympathetic and sympathetic nervous systems. "The parasympathetic system is irresponsible for dilation of the vascular system with allows for vasocongestion," says Swann. (Vasocongestion is a fancy word for the swelling of tissues in the genitals during sex, as a result of increased blood flow.) Meanwhile, the sympathetic nervous system is in charge of retaining urine in the bladder to make sure you don't like, pee when you're having sex or — if you have a penis — when you ejaculate.

Clinical sexologist Lawrence Siegel says "the body really tries to keep these functions separate" because "uric acid is the main constituent of urine (besides water) and can easily damage sperm if they make contact."

Why does one testicle sometimes ascend?

This is a peculiarity experienced by people with testes when they're masturbating. Per Dr. Amin Herati — assistant professor of urology at the Johns Hopkins University School of Medicine — during arousal, "the cremaster muscles that surround the testes start contracting." "The activity of these muscles then leads to the testicles ascending during masturbation," says Herati.

Siegel says that the swelling and ascension of the testes is "necessary to achieve full expulsion or ejaculation." He says that as sexual arousal increases, vasocongestion makes the testes start to swell. As this happens, the cremaster muscle contracts and the testes are drawn up closer to the body.

Why can people with vulvas keep on masturbating after orgasming?

Well, the TL;DR version is this: people with vulvas can have multiple orgasms, and people with penises usually cannot. Carlin Ross — sex educator at the Betty Dodson Foundation — says: "Women are bottomless pits of sexual pleasure because we can orgasm, and orgasm, and orgasm. (Not all people with vulvas identify as women, of course.) "When you keep going, you hit new levels of pleasure building on your orgasm energy and riding the waves until you're a heaving, sweaty mess."

So, why is this? According to Swann, people with vulvas don't have a post-coital refractory period, which means that they remain sensitive to sexual stimuli and can achieve further orgasms.

Why can't people with penises carry on masturbating after they come?

Alas, people with penises aren't typically able to achieve multiple orgasms in a short span of time. This is because they have a refractory period, the period of time it takes to regain sexual sensitivity. "This reduced sensitivity lasts until the body has regained sensitivity to sexual stimuli," says Herati.

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Sex educator Bianca Palmisano says scientists aren't 100 percent certain why this happens, but some hypothesise that the refractory period is regulated by hormones like like oxytocin and prolactin. "Others suggest that ejaculation reduces the tension in the walls of the seminal vesicles, which causes a negative feedback loop to other organs and nerves, preventing re-arousal for a while," says Palmisano.

SEE ALSO: Nice: Here are 50 of the funniest euphemisms for masturbation

Swann says some research has suggested that this refractory period can be "influences by the senses or cognitive factors." "There is a response, known as the Coolidge effect, in rodents in which the male response is restored by the presence of a novel female," says Swann.

Why do you get a red rash on your chest?

Have you ever looked down at your chest after orgasm and seen a red blotchy rash appear? Well, according to Siegel, this response is actually called a "sex flush" and was thus named by the Masters and Johnson research team.

Swann says this rash occurs due to vasocongestion, which not only results in blood flow increasing in one's genitals, it also occurs in "other parts of the body and skin."

Ross says the rash is caused by the "blood vessels in your skin dilating from the orgasm." "An authentic orgasm is accompanied by the release of oxytocin, which reduces cortisol the stress hormone, and oestrogen," says Ross. "It's why orgasm is healthy and necessary to lead a happy life."

Why do previous injuries throb during masturbation?

Ever felt a weird throbbing feeling in body parts you've injured, like a broken foot, say? Herati says this is likely because of the way "the brain perceives the source of stimuli."

If it's your foot that's been throbbing, there could well be a rather curious explanation for that. Per Herati, studies "mapping where genital and foot sensation are perceived by the brain" have found the regions are "in close proximity."

But, if other injured areas are throbbing, it could be a result of vasocongestion, says Wilhite. Blood flow is increased all over the body, and not just in the genitals, during sexual arousal. "Places which have been injured often have an altered blood flow pattern as the result of the injury, so you might be noticing that throbbing more," says Wilhite.

Why does direct clitoral stimulation sometimes feel too intense?

This sometimes happens when using a vibrator. As you near orgasm, the stimulation begins to feel, well, a little too much. Too much of a good thing, perhaps? Ross says that direct clitoral stimulation sometimes feels too intense because you may have "already had a small orgasm and didn't recognise it," or you might need "more lubricant and less pressure."

SEE ALSO: Read these masturbation horror stories at your own risk

Swann says that the clitoris "expands with blood and becomes very sensitive" as stimulation progresses. The clitoris does, however, have a safety mechanism, says Swann. "It retracts into the labial folds to prevent excessive stimulation."

As Wilhite points out, this experience is "pretty subjective," and can, of course, happen "whether a vibrator, hand, washing machine, whatever is being used for stimulation." Wilhite says it happens because the person is "overstimulating the sensory nerve endings which are right at the tip of the clitoris." If it's happening, it might be time to ease off the pressure.

Why is your pee a split stream afterwards?

Split-stream urination can happen to anyone, according to Siegel, but it's "far more prevalent" in people with penises. "After they ejaculate some of the semen remains in the urethra where it thickens and dries out," says Siegel. "This can form a partial obstruction for the flow of urine, particularly if it is a weak stream."

Herati seems to be in agreement with this explanation. "The split stream likely originates from retained ejaculate in the urethra causing the urethral wall to collapse and remain partially collapsed during urination."

Why does your vulva swell up?

The vulva swells up and appears engorged during masturbation because of — you guessed it — increased blood flow! Wilhite says "genital tissue, specifically the clitoral structure, becomes filled with engorged blood and swells under the skin."

This is our body's response to "sexually stimulated vasodilation" — the dilatation of blood vessels — caused by nitric oxide, "a gaseous neurotransmitter/vasodilator produced by either cognitive stimulation, direct stimulation/massage or both."

Now that all your burning questions have been answered, you can get back to doing what you do best — masturbating.

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