The prostate gland is an exocrine gland of the male reproductive system.

The prostate gland differs considerably between species anatomically, chemically, and physiologically.

The main function of the prostate is to store and secrete a clear, slightly basic fluid that constitutes up to one-third of the volume of semen. Semen is composed of sperm and seminal fluid; about 10-30% of the seminal fluid is produced by the prostate gland, the rest is produced by the two seminal vesicles.

The prostate also contains some smooth muscles that helps to expel semen during ejaculation.

Prostatic secretions vary between species. They are generally composed of simple sugars, and are often slightly basic.

In human prostatic secretions, the protein content is less than 1% and includes proteolytic enzymes, acid phosphatase, and prostate-specific antigen. The secretions also contain zinc and citric acid.

To work properly, the prostate needs male hormones (androgens), which are responsible for male sex characteristics.

The main male hormone is testosterone, which is produced mainly by the testicles. Some male hormones are produced in small amounts by the adrenal glands.