What proportion of semen consists of sperm cells?

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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.

In the sexually mature human male, sperm cells constitute only about 2 to 5 percent of the total volume of semen.

The remainder of the ejaculate consists of seminal plasma, which is composed of fluids secreted by various glands in the human reproductive system. Specifically, the seminal vesicles contribute approximately 60 percent of the total volume, while the prostate gland provides about 30 percent. A small additional amount of lubricating fluid is secreted by the bulbourethral glands and urethral glands.12