Why does semen not normally enter the bladder during ejaculation?

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Front view anatomical diagrams of the male and female reproductive systems, with labeled organs including penis, testis, prostate gland, uterus, ovary, and vagina. — human reproductive system Organs and structures of the male and female reproductive systems.

During the process of ejaculation, semen does not enter the urinary bladder because the sympathetic nervous system coordinates the event to prevent this occurrence.1

Specifically, the same sympathetic nerve impulses that trigger the ejaculation reflex simultaneously inhibit the urge to urinate and act to close off the bladder, ensuring that semen is directed through the urethra and expelled from the body rather than flowing backward into the bladder.1