Inside of the prostate, adjacent and parallel to the prostatic urethra, there are two longitudinal muscle systems. The five lobes are the anterior lobe or isthmus, the posterior lobe, the right and left lateral lobes, and the middle or median lobe. The "lobe" classification describes lobes that, while originally defined in the fetus, are also visible in gross anatomy, including dissection and when viewed endoscopically. 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. It is the region of the prostate gland that grows throughout life and causes the disease of benign prostatic enlargement. ~10–20% of prostate cancers originate in this zone. The transition zone surrounds the proximal urethra. 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. This zone surrounds the ejaculatory ducts. About 70–80% of prostatic cancers originate from this zone of the gland. The back of the gland that surrounds the distal urethra and lies beneath the capsule. Zones are more typically able to be seen on histology, or in medical imaging, such as ultrasound or MRI. The prostate has been described as consisting of three or four zones. Because of the variation in descriptions and definitions of lobes, the zone classification is used more predominantly. The internal structure of the prostate has been described using both lobes and zones. The prostate is covered in a surface called the prostatic capsule or prostatic fascia. The part of the urethra passing through it is called the prostatic urethra, which joins with the two ejaculatory ducts. It sits below the urinary bladder and surrounds the urethra. 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 a gland of the male reproductive system. The word prostate comes from Ancient Greek προστάτης, prostátēs, meaning "one who stands before", "protector", "guardian", with the term originally used to describe the seminal vesicles. 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.ĭisorders of the prostate include enlargement, inflammation, infection, and cancer. 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. The alkalinity of semen helps neutralize the acidity of the vaginal tract, prolonging the lifespan of sperm. This prostatic fluid is slightly alkaline, milky or white in appearance. The prostate glands produce and contain fluid that forms part of semen, the substance that is emitted during ejaculation as part of the male sexual response. It is surrounded by an elastic, fibromuscular capsule and contains glandular tissue as well as connective tissue. It is described in gross anatomy as consisting of lobes and in microanatomy by zone. Anatomically, the prostate is found below the bladder, with the urethra passing through it.
It differs between species anatomically, chemically, and physiologically. The prostate is both an accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation.