Composition of Human Semen

Human semen is an organic fluid containing spermatozoa (also known as sperm cells). The semen is produced by the gonads (the sexual glands of males) and discharged by the body through a process called ejaculation in order to make the fertilization of the female ovum possible.

The human semen is composed of sperm cells and seminal plasma. The latter represents a fluid that is produced by the accessory male reproductive organs (the prostate gland, the seminal vesicles and the bulbourethral glands).

The main purpose of the seminal plasma is to feed and protect the spermatozoa through the female reproductive tract till they reach the ovum. This is needed since the environment of the vagina is too acidic for the spermatozoa. Additionally it contains cells that are part of the female immune system and perceive sperm cells as foreign entities.

The bulbourethral glands have a small contribution to the seminal plasma (less than 1%). They produce a viscous secretion during sexual arousal that is known as pre-ejaculate. The pre-ejaculate is needed to lubricate the urethra in order to help the spermatozoa to pass through. Additionally, the galactose and mucus produced by the bulbourethral glands serve to increase the sperm mobility in the vagina and cervix. They create a less viscous channel for the spermatozoa to swim through and prevent spermatozoon diffusion out of the semen.

The prostate is responsible for about 25-30% of the seminal plasma and its secretion is needed in order to stabilize the DNA-containing chromatin in the spermatozoa.

The seminal vesicles produce the largest part of the seminal plasma (about 65-75% of it) which is responsible for feeding the sperm cells during their journey to the ovum and takes part in suppressing the female immune response against the foreign semen.