prostate prostate the prostate 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. 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. this article is about the male prostate gland. for the equivalent female prostate gland, see skene's gland. for the journal, see the prostate. prostatedetailsprecursorendodermic evaginations of the urethraarteryinternal pudendal artery, inferior vesical artery, and middle rectal arteryveinprostatic venous plexus, pudendal plexus, vesical plexus, internal iliac veinnerveinferior hypogastric plexuslymphinternal iliac lymph nodesidentifierslatinprostatameshd011467ta98a09.3.08.001ta23637fma9600anatomical terminology the prostate glands produce and contain 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. 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. 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 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: namefraction of adult glanddescription 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/athis area, not always considered a zone, is usually devoid of glandular components and composed only, as its name suggests, of muscle and fibrous tissue. the "lobe" classification describes lobes that, while originally defined in the fetus, are also visible in gross anatomy, including dissection and when viewed endoscopically. the five lobes are the anterior lobe or isthmus, the posterior lobe, the right and left lateral lobes, and the middle or median lobe. lobes of prostate zones of prostate inside of the prostate, adjacent and parallel to the prostatic urethra, there are two longitudinal muscle systems. on the front side (ventrally) runs the urethral dilator (musculus dilatator urethrae), on the backside (dorsally) runs the muscle switching the urethra into the ejaculatory state (musculus ejaculatorius). blood and lymphatic vessels the prostate receives blood through the inferior vesical artery, internal pudendal artery, and middle rectal arteries. these vessels enter the prostate on its outer posterior surface where it meets the bladder, and travel forward to the apex of the prostate. both the inferior vesical and the middle rectal arteries often arise together directly from the internal iliac arteries. on entering the bladder, the inferior vesical artery splits into a urethral branch, supplying the urethral prostate; and a capsular branch, which travels around the capsule and has smaller branches which perforate into the prostate. the veins of the prostate form a network – the prostatic venous plexus, primarily around its front and outer surface. this network also receives blood from the deep dorsal vein of the penis, and is connected via branches to the vesical plexus and internal pudendal veins. veins drain into the vesical and then internal iliac veins. the lymphatic drainage of the prostate depends on the positioning of the area. vessels surrounding the vas deferens, some of the vessels in the seminal vesicle, and a vessel from the posterior surface of the prostate drain into the external iliac lymph nodes. some of the seminal vesicle vessels, prostatic vessels, and vessels from the anterior prostate drain into internal iliac lymph nodes. vessels of the prostate itself also drain into the obturator and sacral lymph nodes. imaging showing the inferior vesical, inferior pudendal and middle rectal arteries arising from the internal iliac arteries. image showing the external iliac lymph nodes and their positions around the external iliac artery and vein microanatomy micrograph of benign prostatic glands with corpora amylacea. h&e stain. the prostate consists of glandular and connective tissue. tall column-shaped cells form the lining (the epithelium) of the glands. these form one layer or may be pseudostratified. the epithelium is highly variable and areas of low cuboidal or flat cells can also be present, with transitional epithelium in the outer regions of the longer ducts. the glands are formed as many follicles, which drain into canals and subsequently 12–20 main ducts, these in turn drain into the urethra as it passes through the prostate. there are also a small amount of flat cells, which sit next to the basement membranes of glands, and act as stem cells. the connective tissue of the prostate is made up of fibrous tissue and smooth muscle. the fibrous tissue separates the gland into lobules. it also sits between the glands and is composed of randomly orientated smooth-muscle bundles that are continuous with the bladder. over time, thickened secretions called corpora amylacea accumulate in the gland. microscopic glands of the prostate gene and protein expression further information: bioinformatics § gene and protein expression about 20,000 protein coding genes are expressed in human cells and almost 75% of these genes are expressed in the normal prostate. about 150 of these genes are more specifically expressed in the prostate, with about 20 genes being highly prostate specific. the corresponding specific proteins are expressed in the glandular and secretory cells of the prostatic gland and have functions that are important for the characteristics of semen, including prostate-specific proteins, such as the prostate specific antigen (psa), and the prostatic acid phosphatase. development further information: development of the reproductive system in the developing embryo, at the hind end lies an inpouching called the cloaca. this, over the fourth to the seventh week, divides into a urogenital sinus and the beginnings of the anal canal, with a wall forming between these two inpouchings called the urorectal septum. the urogenital sinus divides into three parts, with the middle part forming the urethra; the upper part is largest and becomes the urinary bladder, and the lower part then changes depending on the biological sex of the embryo. the prostatic part of the urethra develops from the middle, pelvic, part of the urogenital sinus, which is of endodermal origin. around the end of the third month of embryonic life, outgrowths arise from the prostatic part of the urethra and grow into the surrounding mesenchyme. the cells lining this part of the urethra differentiate into the glandular epithelium of the prostate. the associated mesenchyme differentiates into the dense connective tissue and the smooth muscle of the prostate. condensation of mesenchyme, urethra, and wolffian ducts gives rise to the adult prostate gland, a composite organ made up of several tightly fused glandular and non-glandular components. to function 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. it is dihydrotestosterone (dht), a metabolite of testosterone, that predominantly regulates the prostate. the prostate gland enlarges over time, until the fourth decade of life. function the prostate secretes fluid which becomes part of semen. semen is the fluid emitted (ejaculated) by males during the sexual response. when sperm is emitted, it is transmitted from the vas deferens into the male urethra via the ejaculatory ducts, which lie within the prostate gland. ejaculation is the expulsion of semen from the urethra. semen is moved into the urethra following contractions of the smooth muscle of the vas deferens and seminal vesicles, following stimulation, primarily of the glans penis. stimulation sends nerve signals via the internal pudendal nerves to the upper lumbar spine; the nerve signals causing contraction act via the hypogastric nerves. after traveling into the urethra, the seminal fluid is ejaculated by contraction of the bulbocavernosus muscle. the secretions of the prostate include proteolytic enzymes, prostatic acid phosphatase, fibrinolysin, zinc, and prostate-specific antigen. together with the secretions from the seminal vesicles, these form the major fluid part of semen. it is possible for some men to achieve orgasm solely through stimulation of the prostate gland, such as via prostate massage or anal intercourse. this has led to the area of the rectal wall adjacent to the prostate to be popularly referred by the anatomically incorrect term, the "male g-spot". the prostate's changes of shape, which facilitate the mechanical switch between urination and ejaculation, are mainly driven by the two longitudinal muscle systems running along the prostatic urethra. these are the urethral dilator (musculus dilatator urethrae) on the urethra's front side, which contracts during urination and thereby shortens and tilts the prostate in its vertical dimension thus widening the prostatic section of the urethral tube, and the muscle switching the urethra into the ejaculatory state (musculus ejaculatorius) on its backside. in case of an operation, e.g. because of benign prostatic hyperplasia (bph), damaging or sparing of these two muscle systems varies considerably depending on the choice of operation type and details of the procedure of the chosen technique. the effects on postoperational urination and ejaculation vary correspondingly. 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