Semen, or seminal fluid, is the thick, viscid secretion released by the male at orgasm. Its main purpose is for reproduction. It contains sperm and seminal plasma, which is composed of the contributions of four glands: the testes, the seminal vesicle, the prostate and the bulbourethral. The plasma provides a nutritive, highly alkaline and very protective medium for the sperm during their trip through the female reproductive tract, as the vagina is extremely acidic and hostile.

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