Semen

Semen is the whitish, usually opaque fluid ejaculated by the male reproductive system. In humans it consists of spermatozoa suspended in seminal plasma and is produced by multiple organs of the male reproductive tract. Sperm originate in the testes, where germ cells develop within the seminiferous tubules and mature as they move through the epididymis. The bulk of the seminal plasma comes from the seminal vesicles and the prostate gland, with additional contributions from the bulbourethral glands and the urethral lining. The seminal vesicles provide fructose and prostaglandins; the prostate adds citrate, zinc, and enzymes; the bulbourethral glands contribute mucus that lubricates the urethra and helps neutralize residual acidity.

During ejaculation, sperm pass from the epididymis into the vas deferens and mix with secretions from the accessory glands to form semen. Typical semen volume ranges from about 1.5 to 5 milliliters per ejaculation; sperm concentration is roughly 15 to 150 million per milliliter, giving a total sperm count commonly cited as about 40 to 300 million per ejaculate. Seminal plasma contains buffers to maintain a pH around 7.2 to 8.0 and provides nutrients, enzymes, and protective proteins to support sperm viability and motility.

Functionally, semen delivers sperm to the female reproductive tract and provides a milieu that supports sperm survival during transit. In clinical settings, semen analysis assesses volume, concentration, total count, motility, morphology, and pH to evaluate male fertility. Factors such as illness, fever, smoking, excessive alcohol use, obesity, and certain medications can affect semen quality. Semen samples may carry pathogens, so proper handling is required in medical and research contexts.