Ejaculation is when a male person (or other male mammal) shoots out liquid from his erect penis after it has been aroused or stimulated (excited sexually). It happens when he has an orgasm. This article is about ejaculation in human beings.

When a man is stimulated, his penis becomes erect. When he has an orgasm, semen comes out from the end of his penis. Semen contains sperm and other substances. How long a man can be stimulated before ejaculating, how long the ejaculation lasts, the strength of the ejaculation, and the amount of semen that comes out, all vary from one man to another. When a man ejaculates, he has a very good feeling in his penis and his groin area (the part of his body where his torso joins the top of his legs). A man can ejaculate after he masturbates, is touched by someone else sexually, and sometimes, even if he is not touched (for example, if he looks at pictures and videos on the internet that cause sexual arousal, or thinks about sex). Ejaculation can also happen without control when a man is sleeping, which is called a wet dream.
Urine can sometimes also come out with the ejaculatory fluid during sex.
Boys usually do not ejaculate until they reach puberty but sometimes it can happen before.

Slang terms for ejaculation are blowing a load or blowing a wad, and busting a nut. creaming, cumming, jizzing, nutting, jazzing, spurting, squirting and skeeting. Ejaculation takes place when the man has an orgasm (the height of sexual excitement), usually after his genitals have been physically stimulated in some way. However, ejaculation can also happen if a man has not been touched, for instance if he becomes aroused or stimulated (made sexually excited) by looking at sexy pictures, watching sexy videos, or thinking about sex. When a man ejaculates while sleeping, it is called nocturnal emission.

How it happens 

Before a man can ejaculate, his penis needs to be stimulated. The penis is usually soft, quite short and hangs down. When a man is stimulated, for example by seeing another naked person, masturbating or being touched by someone else sexually, the inside of his penis fills with blood. This causes it to become longer, thicker, harder and to stand upright, and is called an erection. Men can be stimulated for different amounts of time before they ejaculate.

Ejaculation takes place in two stages.
 First stage: Emission. The first stage is called emission (which means "the act of sending or throwing something out"). A man's testicles make sperm cells, and these are stored in a coiled tube called the epididymis. During emission, the two ducts (tubes) called the vasa deferentia (each tube by itself is called a vas deferens), which carry sperm away from the testicles, squeeze the sperm from the epididymis to the top end of the ducts. When this happens, the man feels that he cannot stop his ejaculation. It is sometimes said that the man has reached the "point of no return". The sperm then passes through other tubes called the ejaculatory ducts, where they are mixed with fluids made by glands called the seminal vesicles, the prostate and the bulbourethral glands (also called Cowper's glands). (Glands are special body organs that make chemicals.) The mixture of sperm and fluid is called semen or ejaculate. It is white or yellowish, and sticky.
 Second stage: Ejaculation proper. The second stage is called ejaculation proper (which means "real ejaculation"). When ejaculation proper begins, the man starts having an orgasm. A muscle at the base of the man's penis called the bulbospongiosus muscle squeezes strongly again and again. This forces semen to move from the ejaculatory ducts into the urethra, which is a duct that passes right through the penis. Semen is pushed along the urethra until it shoots out of the end of the penis in spurts. Once the muscle starts to squeeze, the man cannot stop the semen from coming out of his penis. During an orgasm, the man's muscle will usually squeeze about 10 to 15 times. The squeezes happen very quickly. They start at about 0.6 second apart, then slow down and become weaker. Most of the semen is ejaculated in the first few squeezes. How strong an ejaculation is varies from man to man. For some men the semen shoots out of their penis very far, while for others it dribbles out. An ejaculation is often stronger if a man has been stimulated for a longer time. The squeezing of the man's muscle gives a very good feeling to his penis and his groin area (the part of his body where his torso joins the top of his legs). A man's orgasm usually lasts about 17 seconds, but some men have an orgasm for only a few seconds while for others it can last for up to one minute.

After a man has ejaculated, his penis usually becomes soft and shorter again. He may also have an enjoyable and relaxing feeling in his groin area. It takes some time before he can have another erection and ejaculation. This time is called the refractory period. The average refractory period is about half an hour. Younger men normally have a shorter refractory period than older men. Men who are 18 years old have a refractory period of about 15 minutes, while men in their 70s have one of about 20 hours. Some men's penises remain hard after one ejaculation, and they are able to have another ejaculation after some time without losing their erection. Most young and middle-aged men can probably have about two to three ejaculations in a few hours, but it has been said that some men are able to have up to nine ejaculations a day.

When a man ejaculates before he wants to, this is called premature ejaculation. If a man cannot ejaculate after having been aroused for a long time, even though he wants to, this is called delayed ejaculation or anorgasmia. A man who is unable to ejaculate at all is said to have anejaculation. Some men are able to have an orgasm without ejaculating. This is called a dry orgasm.

Apart from giving a man pleasure, ejaculation may help a man stay healthy. A study carried out in Australia seemed to show that men who ejaculate often have less chance of getting prostate cancer.

Semen

Semen is known informally as cum, jism or jizz. Men ejaculate different amounts of semen. Normally, an ejaculation makes between 1.5 and 5 millilitres (up to one teaspoonful) of semen. More semen tends to come out if a man has not ejaculated for many days, or if he has been stimulated for a long time. Older men produce less semen. If a man ejaculates an unusually small amount of semen, this is a medical condition called hypospermia.

Semen is usually a white or yellowish fluid. It starts off being slightly thick and sticky, then after a while it becomes more watery. Semen contains many chemicals. These include citric acid, fructose (a type of sugar), enzymes that speed up chemical reactions in the body, lipids (substances that fat is made of), and slippery fluids that help the semen to move through the urethra.

The number of sperm in an ejaculation of semen depends on many things. There may be more sperm if:
 the man is younger,
 his body produces more of the hormone testosterone, which makes a person look and feel like a man,
 his testicles are not too warm,
 he produces more semen,
 he has not ejaculated for some time, and
 he has been stimulated for a longer time before ejaculation.

If there are an unusually low number of sperm in an ejaculation, this is called oligospermia. If there are no sperm at all, this is called azoospermia. A man with oligospermia or azoospermia is usually infertile, and cannot or finds it very hard to make a woman pregnant by having sex with her.

If a man has a sexually transmitted infection or STI (an infection that is passed from one person to another by sex), the germs that cause the disease can appear in his semen. If the person that the man has sex with touches the semen, he or she can become infected by the germs and pick up the disease. AIDS, gonorrhea, hepatitis B, herpes and syphillis are examples of STIs. One of the ways for a man to lower the chance of passing on an STI to his sexual partner is to wear a condom on his penis when having sex.

Fertilization

When a man has sexual intercourse with a woman, he places his penis within her vagina and moves his penis back and forth, typically in a thrusting motion, while the woman moves her hips. The vagina is warm and somewhat moist, and it places pressure on the man's penis. These sensations, combined with the friction caused by the in-and-out movements, stimulates the penis, which causes the man to have an orgasm and to ejaculate. If the woman is using birth control this will usually not cause her to become pregnant. Otherwise, the sperm in the semen can travel into the woman's uterus and Fallopian tubes. If there happens to be an ovum or egg cell in a Fallopian tube, a sperm may fuse with the ovum. This is called fertilization, and makes the woman pregnant.

However, before a man ejaculates, a clear, colorless, sticky fluid called pre-ejaculate (also known as pre-ejaculate fluid or informally as pre-cum) can come out of his penis. Pre-ejaculate is produced by the bulbourethral or Cowper's glands. Some tests have shown that pre-ejaculate does not contain any sperm. However, some sperm may have been left behind in the urethra from an earlier ejaculation and the pre-ejaculate may carry this sperm out of the penis. That is why a woman can become pregnant even if the man pulls his penis out of her vagina before he ejaculates. Also, if a man ejaculates near the woman's vagina and semen falls on her body, sperm can accidentally enter the vagina and cause a pregnancy. To avoid the woman becoming pregnant when she does not want to, the man and the woman can use methods of contraception or birth control. For example, the man can wear a condom on his penis, or the woman can take birth control pills.

First ejaculation
Young boys cannot ejaculate. A boy's first ejaculation usually happens about one year after he begins puberty, which is when his body starts changing into a man's body. Most boys go through puberty in their teens. The first time a boy ejaculates usually happens when he is asleep. This is called a nocturnal emission (which means "an emission happening at night") or a wet dream. It happens without the boy's control, often when he is having a dream about sex. Scientists believe that wet dreams are the body's way of removing too much semen. When a boy begins masturbating, wet dreams usually stop happening.

When a boy starts to ejaculate, he usually produces only a small amount of semen. The semen is different from what an adult man produces. It is usually clear and stays sticky. It either has no sperm in it, or sperm that do not move properly or do not move at all. A boy's semen only becomes like an adult man's semen about two years after his first ejaculation.

References 

Male reproductive system