Prostate

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For the journal, see The Prostate.
Not to be confused with Prostrate (body position).

Prostate
pudendal plexus, vesical plexus, internal iliac vein
NerveInferior hypogastric plexus
Lymphinternal iliac lymph nodes
Identifiers
Latinprostata
MeSHD011467
TA98A09.3.08.001
TA23637
FMA9600
Anatomical terminology]

The prostate (

microanatomy by zone. It is surrounded by an elastic, fibromuscular capsule and contains glandular tissue, as well as connective tissue
.

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

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.[3] The prostate is covered in a surface called the prostatic capsule or prostatic fascia.[5]

The internal structure of the prostate has been described using both lobes and zones.[6][3] Because of the variation in descriptions and definitions of lobes, the zone classification is used more predominantly.[3]

The prostate has been described as consisting of three or four zones.[3][5] Zones are more typically able to be seen on histology, or in medical imaging, such as ultrasound or MRI.[3][6] The zones are:

Name Fraction of adult gland[3] 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.[7][8]
Central zone (CZ) 20% This zone surrounds the ejaculatory ducts.[3] 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.[9]
Transition zone (TZ) 5% The transition zone surrounds the proximal urethra.
benign prostatic enlargement.[7][8]
Anterior fibro-muscular zone (or
stroma
)		 N/A This area, not always considered a zone,
fibrous tissue.[3]

The "lobe" classification describes lobes that, while originally defined in the fetus, are also visible in gross anatomy, including dissection and when viewed endoscopically.[6][5] 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
    Lobes of prostate
  • Zones 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).[10]

Blood and lymphatic vessels

The prostate receives blood through 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.[5]

The veins of the prostate form a network – the

deep dorsal vein of the penis, and is connected via branches to the vesical plexus and internal pudendal veins.[5] Veins drain into the vesical and then internal iliac veins.[5]

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.[5] Some of the seminal vesicle vessels, prostatic vessels, and vessels from the anterior prostate drain into internal iliac lymph nodes.[5] Vessels of the prostate itself also drain into the obturator and sacral lymph nodes.[5]

  • Imaging showing the inferior vesical, inferior pudendal and middle rectal arteries arising from the internal iliac arteries.
    Imaging showing the
    internal iliac arteries
    .
  • Image showing the external iliac lymph nodes and their positions around the external iliac artery and vein
    Image showing the
    vein

Microanatomy

Micrograph of benign prostatic glands with corpora amylacea. H&E stain.

The prostate consists of glandular and

flat cells can also be present, with transitional epithelium in the outer regions of the longer ducts.[11] Basal cells surround the luminal epithelial cells in benign glands. 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.[5] There are also a small amount of flat cells, which sit next to the basement membranes of glands, and act as stem cells.[3]

The connective tissue of the prostate is made up of fibrous tissue and smooth muscle.[3] The fibrous tissue separates the gland into lobules.[3] It also sits between the glands and is composed of randomly orientated smooth-muscle bundles that are continuous with the bladder.[12]

Over time, thickened secretions called corpora amylacea accumulate in the gland.[3]

  • Microscopic glands of the prostate
    Microscopic glands of the prostate
  • Microanatomy of a prostatic gland, showing both luminal cells and surrounding basal cells. H&E stain.
    Microanatomy of a prostatic gland, showing both luminal cells and surrounding basal cells. H&E stain.

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.[13][14] About 150 of these genes are more specifically expressed in the prostate, with about 20 genes being highly prostate specific.[15] 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.[16]

Development

Further information: Development of the reproductive system

In the developing

urinary bladder, and the lower part then changes depending on the biological sex of the embryo.[17]

The prostatic part of the urethra develops from the middle, pelvic, part of the urogenital sinus, which is of

smooth muscle of the prostate.[19]

Condensation of

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.[5]

Function

In ejaculation

The prostate secretes fluid, which becomes part of the

proteolytic enzymes, prostatic acid phosphatase, fibrinolysin, zinc, and prostate-specific antigen.[5] Together with the secretions from the seminal vesicles, these form the major fluid part of semen.[5]

In urination

See also: Surgery for benign prostatic hyperplasia

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,[21][22] and the muscle switching the urethra into the ejaculatory state (musculus ejaculatorius) on its backside.[10]

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.[23]

In stimulation

It is possible for some men to achieve orgasm solely through stimulation of the prostate gland, such as via prostate massage or anal intercourse.[24][25] 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".[26]

Clinical significance

Inflammation

leukocytes, can be seen. An area without inflammation is seen on the left of the image. H&E stain
.
Main article: Prostatitis

urine culture.[27]

Acute prostatitis and chronic bacterial prostatitis are treated with

trigger point and psychological therapy has proved effective for category III prostatitis as well.[28]

Enlarged prostate

A digital rectal examination may be performed to investigate how large a prostate is
A diagram of prostate cancer pressing on the urethra, which can cause symptoms
Micrograph showing normal prostate cancer in the right upper aspect of image. HPS stain. Prostate biopsy.
Main articles:
Prostatomegaly and Benign prostatic hyperplasia

An enlarged prostate is called

urinary hesitancy). If the prostate grows too large, it may constrict the urethra and impede the flow of urine, making urination painful and difficult, or in extreme cases completely impossible, causing urinary retention.[27] Over time, chronic retention may cause the bladder to become larger and cause a backflow of urine into the kidneys (hydronephrosis).[27]

BPH can be treated with medication, a minimally invasive procedure or, in extreme cases, surgery that removes the prostate. In general, treatment often begins with an alpha-1 adrenergic receptor antagonist medication such as tamsulosin, which reduces the tone of the smooth muscle found in the urethra that passes through the prostate, making it easier for urine to pass through.[27] For people with persistent symptoms, procedures may be considered. The surgery most often used in such cases is transurethral resection of the prostate,[27] in which 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. Minimally invasive procedures include transurethral needle ablation of the prostate and transurethral microwave thermotherapy.[30] These outpatient procedures may be followed by the insertion of a temporary stent, to allow normal voluntary urination, without exacerbating irritative symptoms.[31]

Cancer

Main article: Prostate cancer

Prostate cancer is one of the most common cancers affecting older men in the UK, US, Northern Europe and Australia, and a significant cause of death for elderly men worldwide.[32] Often, a person does not have symptoms; when they do occur, symptoms may include urinary frequency, urgency, hesitation and other symptoms associated with BPH. Uncommonly, such cancers may cause weight loss, retention of urine, or symptoms such as back pain due to metastatic lesions that have spread outside of the prostate.[27]

A

bone scan may be done to check for the presence of tumour metastases in other parts of the body.[27]

Prostate cancer that is only present in the prostate is often treated with either surgical

Radiotherapy may also be used to help with pain associated with bony lesions.[27]

Sometimes, the decision may be made not to treat prostate cancer. If a cancer is small and localised, the decision may be made to monitor for cancer activity at intervals ("active surveillance") and defer treatment.[27] If a person, because of frailty or other medical conditions or reasons, has a life expectancy less than ten years, then the impacts of treatment may outweigh any perceived benefits.[27]

Surgery

Main article: Prostatectomy

Surgery to remove the prostate is called

pubic bone.[35] Open surgery may be preferred if there is a suspicion that lymph nodes are involved and they need to be removed or biopsied during a procedure.[35] A perineal approach will not involve lymph node removal and may result in less pain and a faster recovery following an operation.[35] A TURP procedure uses a tube inserted into the urethra via the penis and some form of heat, electricity or laser to remove prostate tissue.[35]

The whole prostate can be removed. Complications that might develop because of surgery include

blood clots.[35]

History

The prostate was first formally identified by

Andreas Vesalius in Tabulae anatomicae sex (six anatomical tables) in 1538.[37][6] Massa described it as a "glandular flesh upon which rests the neck of the bladder," and Vesalius as a "glandular body".[38] The first time a word similar to 'prostate' was used to describe the gland is credited to André du Laurens in 1600, who described it as a term already in use by anatomists at the time.[38][6] The term was however used at least as early as 1549 by French surgeon Ambroise Pare.[6]

At the time, Du Laurens was describing what was considered to be a pair of organs (not the single two-lobed organ), and the

gender of the Ancient Greek term was taken as female, when it was in fact male.[38]

The fact that the prostate was one and not two organs was an idea popularised throughout the early 18th century, as was the English language term used to describe the organ, prostate,[38] attributed to William Cheselden.[39] A monograph, "Practical observations on the treatment of the diseases of the prostate gland" by Everard Home in 1811, was important in the history of the prostate by describing and naming anatomical parts of the prostate, including the median lobe.[38] The idea of the five lobes of the prostate was popularized following anatomical studies conducted by American urologist Oswald Lowsley in 1912.[6][39] John E. McNeal first proposed the idea of "zones" in 1968; McNeal found that the relatively homogeneous cut surface of an adult prostate in no way resembled "lobes" and thus led to the description of "zones".[40]

Prostate cancer was first described in a speech to the

Theodore Billroth in 1867.[39]

Charles B. Huggins published studies in which he used estrogen to oppose testosterone production in men with metastatic prostate cancer. This discovery of "chemical castration" won Huggins the 1966 Nobel Prize in Physiology or Medicine.[48]

The role of the

5-fluorouracil was quickly joined by multiple regimens using a host of other systemic chemotherapy drugs.[52]

Other animals

The prostate is found only in mammals.[53] The prostate glands of male marsupials are proportionally larger than those of placental mammals.[54] The presence of a functional prostate in monotremes is controversial, and if monotremes do possess functional prostates, they may not make the same contribution to semen as in other mammals.[55]

The structure of the prostate varies, ranging from

cetaceans (whales, dolphins, porpoises), the prostate is composed of diffuse urethral glands[66] and is surrounded by a very powerful compressor muscle.[67]

The prostate gland originates with tissues in the urethral wall.[citation needed] This means the urethra, a compressible tube used for urination, runs through the middle of the prostate; enlargement of the prostate can constrict the urethra so that urinating becomes slow and painful.[68]

Prostatic secretions vary among species. They are generally composed of simple sugars and are often slightly alkaline.[69] In eutherian mammals, these secretions usually contain fructose. The prostatic secretions of marsupials usually contain n-Acetylglucosamine or glycogen instead of fructose.[70]

Skene's gland

Because the

embryological tissues),[73][74] various aspects of its development in relation to the male prostate are widely unknown and a matter of research.[75]

See also

References

Citations

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General and cited sources
Attribution

External links

  • Media related to Prostate at Wikimedia Commons
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