I've had it happen and no it doesn't hurt. It's actually pretty cool. Kind of, "Wonder where they went??"
Ladies: Here's the deal with ejaculation. Throughout the stimulation process a lot of different things happen.
1) Penis elongates, gains erection. At that time the sphincter to the bladder is forced closed preventing any leakage of urine. This is essential because....
2) The cowpers glands, two small pea-sized glands at the base of the penis begin to release a clear, viscous, liquid lubricant that spreads not only through the penis but into the seminal vesicles. This is precum. Not only does it lubricate the penis but it also changes the pH of the penis from acid to alkaline. Urine is very acidic and will kill sperm it comes into contact with. The precum neutralizes the acid and lubricates the penis so that when semen is ejaculated, it has a nice slippery and pH friendly tube to make the home run.
3) The prostate begins to swell and release prostatic fluid. This is the pearly fluid you see in ejaculate. The seminal vesicles also being to secrete their contribution to the final...product? Anyway, the prostate creates the sugary fluid that fuels the little guys. It also secretes prostoglandins that stimulate the cervix to dilate and thus allow the swimmers into the holiest-of-holys. And here you thought men weren't that smart. There are also other trace elements and hormones the prostate releases to run interference. They cause the vagina to stop producing lubrication. The pH of the vagina is actually pretty hostile to sperm and, as you already know, the flow of vaginal fluid is in the exact opposite direction the boys want to go. By using these chemical queues, semen helps the sperm get where it's going.
About 10-30% of semen is composed of prostatic fluid.
4) The seminal vesicles lie between the prostate and the cowper's glands. They primarily secrete fructose to power sperm on their way. Their secretion is the clear stuff in semen. It's composed of mucous, vitamin C, other prostaglandins (which primarily tell the sperm to start and keep swimming).
About 70% of semen is composed of fluid from the seminal vesicles.
5) Sperm are just that, sperm. Each testicle produces both male and femal sperm. Not only to the testes create sperm but they also produce testosterone and other auxilliary hormones that make men, men. They're responsible for puberty. All that hair, muscles, more hair, deep voice, broad shoulders, and adult plumbing....and yet more hair... are all tied to the hormones released by the testes.
So after the penis gets erect and the cowpers glands get working on prepping the plumbing, other things start swelling too. The prostate and seminal vesicles begin secreteing their fluids which build-up at the base of the penis. The testes being sending the sperm on a very long trip up through the testicles, OVER the bladder, around back of that, there to the seminal vesicles. This means the sperm doesn't have a direct link to the penis. Sperm has to blend with prostatic, seminal vesicle, and cowper's fluid BEFORE it even gets to the penis! It's very round-about.
So all these things start building pressure. Remember blue balls? They really do exist. It's vasocongestion. As all these organs start working overtime for the big event they need more blood to power their work, hence the whole area becomes full of blood, not just the penis.
At the plateau phase, the stage just before ejaculation, the testicles pull up tighter to the body, some men get a 'sex flush' where their chest, face, neck and arms get a flushed look, and that's when all those fluids being produced meet at the base of the penis, ready for their moon shot.
At ejaculation the organs contract, the main muscle in play here is the pubococcygeus muscle. It's the one you squeeze when doing Kegels. This is the muscle that propels the semen from the base of the penis and the rest of the organs, through the penis and into the vagina. Contractions range in number from 3-10, though not all will expel semen. During the contractions, orgasm may occur. Men can orgasm without ejaculating and vice versa though it's rare. The feeling of ejaculating is pretty intense. You just feel this rush of fluid through your perineum area and through the penis. It comes in spasm with each spasm usually being a release though sometimes they aren't timed together at all. This is particularly true when semen's been building for some time and you just shoot a huge load.
Speaking of shooting, how far a man ejaculates depends on age, health, arousal, and amount of semen being expelled. The more hydrated, healthy, and in-shape your PC muscle is, the more forcefully a man can shoot. Some guys are disposed to dribble, some can shoot 6 feet or more frequently. The PC muscle also helps control orgasm. Doing Kegels allows a man to train at keeping it closed and so can give added force to the ejaculation by holding the PC muscle closed for a brief moment after ejaculation contractions start. This causes the fluid to build-up at the bottom of the penis, building pressure, so when the PC is released, semen shoots out with force. I don't know if women care about it, but shooting with force makes guys feel more masculine.
Some facts about the stuff courtesy of
Wikipedia:
Average volume of semen per ejaculation: 2 to 6 ml (0.41 to 1.22 US teaspoons)
Average number of calories in a tablespoon of semen: 2-7
Average duration of orgasm: 8 seconds
Average number of sperm cells in the ejaculate of a healthy man: 40 million to 600 million (avg. 250 million)
Distance sperm travels to fertilize an egg: 7.5-10 centimeters or 3-4 inches
Sperm lifespan: 2.5 months from development to ejaculation
Sperm lifespan after ejaculation: 30 seconds to 6 days depending on conditions
Now get this. After ejaculation a whole host of things can happen. Some guys, if sufficiently aroused, can stay hard and keep going. Most though, see the penis deflate nearly immediately. As the penis goes down it may expel unejaculated fluid. The testes descend into the scrotum again, the scrotum deflates and goes back to whatever state it was in depending on the temperature of the testicles, blood rushes out of the area, and fluid traffic returns to normal. The previously blocked bladder goes back to getting access to the penis again, and guys roll over and go to sleep.
Why does that happen? Why don't guys like to cuddle and talk and play afterwards? There's a reason! A chemical reason! After orgasm, both men and women release the chemicals oxytocin, prolactin, gamma amino butyric acid. All of these chemicals are brain pacifiers and are the same ones released by the female in lactated milk. Why do babies fall asleep while or right after nursing? These chemicals are part of it. Women process them as pleasure-inducing and give a warm feeling of contentment. Men process them as sleep triggers and usually conk out or go find something else to do. As stated by Mark Leyner, co-author of,
Why Do Men Fall Asleep After Sex?, "People have no idea how much work it is for a man to produce an ejaculation. You have this seminal vesicle churning out this fluid, the prostate gland producing an alkaline solution. It's like having five iron chefs in your crotch working to cook up this stuff."
Males are pretty nifty.
