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The prostate is a gland that is part of male mammalian sex organs. Its main function is to secrete and store a clear, slightly basic fluid that is part of semen. The prostate differs considerably between species anatomically, chemically and physiologically. A healthy human prostate is slightly larger than a walnut. It surrounds the urethra just below the urinary bladder. It is located in front of the rectum and part of it can be felt during a rectal exam.

The male urethra has two functions: to carry urine from the bladder during urination and to carry semen during ejaculation. Within the prostate, the urethra coming from the bladder merges with the two ejaculatory ducts. 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 muscle tissue which 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 <1%.

To work properly, the prostate needs male hormones (androgens). Male hormones 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.

Prostate glands are found only in males; Skene's glands in females are homologous to the prostate gland in males.

Disorders of the prostate

Inflammation of the prostate gland is known as prostatitis. If the prostate grows too large it may constrict the urethra and impede the flow of urine, making urination difficult and painful and in extreme cases completely impossible. Prostatitis is treated with antibiotics, prostate massage or surgery.

In older men, the prostate often enlarges to the point where urination becomes difficult. This is known as benign prostatic hyperplasia and can be treated with medication or with surgery that removes part of the prostate. The surgery most often used in such cases is called transurethral resection of the prostate (TURP or TUR). In TURP, an instrument is inserted through the urethra to remove prostate tissue that is pressing against the upper part of the urethra and restricting the flow of urine.

Prostate cancer is one of the most common cancers affecting elderly men in developed countries and a major cause of death. Regular rectal exams are recommended for elderly men to detect prostate cancer early. There is also a blood test that measures the concentration of a protein, Prostate Specific Antigen (PSA), which is normally very low. Raised test results may be an indicator of disorder within the prostate, either prostatitis, benign hyperplasia or prostate cancer. The PSA test cannot distinguish between them, but can lead a doctor to investigate further. Prostate cancer is treated with radiation and/or surgery.

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