Emission of semen from the penis at orgasm. Shortly before ejaculation, the muscles around the epididymides (the ducts where sperm are stored; see epididymis), the prostate gland, and the seminal vesicles contract rhythmically, forcing the sperm from the epididymides to move forwards and mix with secretions from the seminal vesicles and prostate. At ejaculation, this fluid is propelled through the urethra and out of the body. Because both semen and urine leave the body by the same route, the bladder neck closes during ejaculation. This not only prevents ejaculate from going into the bladder but also stops urine from contaminating the semen (See also reproductive system, male.)


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