May 20 2009

The Anatomy of Intercourse

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What happens to the penis and vagina during sexual intercourse? The answer to this came from a study about using an MRI to see what goes on inside our bodies: Magnetic resonance imaging of male and female genitals during coitus and female sexual arousal. The problems with achieving intercourse inside a fMRI tube cannot be underestimated, especially with a bunch of observers in the next room that is studying your every move:

  • Only missionary position can be used
  • It is basically sex on demand
  • Most men lost their erections
  • For successful scans, the men had to take ED medicines (Viagra)
  • Anybody that had an MRI done knows that it is a cold hard place with lots of things you can bump into

13 sessions were studied. 8 Couples and 3 single women.

The drawing that Leonardo Da Vincy made, of male and female genitals during intercourse, around 1493 is surprisingly accurate for somebody that could not see inside the body.

Intercourse as visualized by Da Vincy

Intercourse as visualized by Da Vincy

What We Know?

We already knew from previous studies that:

  • The Uterus elevates in the body cavity and change the orientation of the cervix
  • The clitoris pulls back inside the body close to orgasm due to it being pulled on by muscles that are tightening and pulling on it close to orgasm

What Is New?

After this study we now know that:

  • The penis bends to form the shape of a boomerang inside the vagina
  • The cervix/uterus changes position during intercourse, to the point where the penis will go well beyond the cervix into the vagina
  • During solo masturbation, the uterus changes position much less
  • The female’s bladder fills rapidly with fluid during sexual activity
  • The uterus does not increase in size, thickens or blows up. Not during sex or during masterbation. The reason why scientists thought that the uterus blows up during sexual stimulation is that the bladder filling with urine causes that illusion

What is Up With the Urge to Pee – Bladder filling up during sexual stimulation

Have you ever had to pee during or after sex or masturbation? You are not alone. This is quite common, and on the MRI scans you can see the woman’s bladder fill up rapidly. Research over the last 15 years found that almost all fluid released during female squirting or gushing is urine. This will be consistent with the observation of the bladder filling. Stimulation of the so calledg-spot is likely putting more presure on the bladder and bladder sphinchter muscle, causing the release of this fluid during sexual stimulation.

Full Bladder During Sex

During arousal and stimulation, the woman’s bladder (B) fills rapidly, producing that feeling that she has to pee close to orgasm or after orgasm.

The reason for this may be a defense mechanism against infections. The female uretharis very short (the path from the pee hole to the bladder). For this reason women are much more susseptable to Urinary Tract Infections (UTIs). Especially since the anus is literally just around the corner, and there are a lot of rubbing over the pee hole during sex. So it is in women’s best interest to pee immediately ufter sex to flush all bacteria and impurities out befoe they get to the bladders or even deeper. So this may be an evolutionary trait thet develooed as a self defense mechanism to prevent nasty infections.

 

 

 

Reference:

BMJ 1999; 319 doi: https://doi.org/10.1136/bmj.319.7225.1596 (Published 18 December 1999) Cite this as: BMJ 1999;319:1596

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