Prostate
The prostate (/ˈprɒs.teɪt/)[1] is both an accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found in all male mammals.[2] It differs between species anatomically, chemically, and physiologically. Anatomically, the prostate is found below the bladder, with the urethra passing through it. It is described in gross anatomy as consisting of lobes and in microanatomy by zone. It is surrounded by an elastic, fibromuscular capsule and contains glandular tissue, as well as connective tissue.
The prostate produces and contains fluid that forms part of semen, the substance emitted during ejaculation as part of the male sexual response. This prostatic fluid is slightly alkaline, milky or white in appearance. The alkalinity of semen helps neutralize the acidity of the vaginal tract, prolonging the lifespan of sperm. The prostatic fluid is expelled in the first part of ejaculate, together with most of the sperm, because of the action of smooth muscle tissue within the prostate. In comparison with the few spermatozoa expelled together with mainly seminal vesicular fluid, those in prostatic fluid have better motility, longer survival, and better protection of genetic material.
Disorders of the prostate include enlargement, inflammation, infection, and cancer.
Structure
The prostate is a gland of the male reproductive system. In adults, it is about the size of a walnut, and has an average weight of about 11 grams, usually ranging between 7 and 16 grams. The prostate is located in the pelvis. It sits below the urinary bladder and surrounds the urethra. The part of the urethra passing through it is called the prostatic urethra, which joins with the two ejaculatory ducts. The prostate is covered in a surface called the prostatic capsule or prostatic fascia.
The internal structure of the prostate has been described using both lobes and zones. Because of the variation in descriptions and definitions of lobes, the zone classification is used more predominantly.
The prostate has thus been described as consisting of three or four zones. Zones are more typically able to be seen on histology, or in medical imaging, such as ultrasound or MRI. The zones are:
| Name | Fraction of adult gland | Description |
| Peripheral zone (PZ) | 70% | The back of the gland that surrounds the distal urethra and lies beneath the capsule. About 70–80% of prostatic cancers originate from this zone of the gland. |
| Central zone (CZ) | 20% | This zone surrounds the ejaculatory ducts. The central zone accounts for roughly 2.5% of prostate cancers; these cancers tend to be more aggressive and more likely to invade the seminal vesicles. |
| Transition zone (TZ) | 5% | The transition zone surrounds the proximal urethra. ~10–20% of prostate cancers originate in this zone. It is the region of the prostate gland that grows throughout life and causes the disease of benign prostatic enlargement |
| Anterior fibro-muscular zone (or stroma) | N/A | This area, not always considered a zone, is usually devoid of glandular components and composed only, as its name suggests, of muscle and fibrous tissue |