About the size of a chestnut, it sits quietly directly below the bladder. In ordinary life a man has almost no occasion to be aware of it as a part of his own body. Yet with each ejaculation this gland reliably works; with age it quietly enlarges; and it sometimes becomes the seedbed of a malignant tumour. In recent years, moreover, it is being rediscovered as the core region of male internal erogenous sensation.

Zenritsusen (前立腺; Latin prostata; English prostate) is a male accessory sex gland (glandula accessoria genitalis) located within the male pelvic cavity. It sits directly below the bladder and develops so as to surround the proximal part of the urethra. It secretes prostatic fluid, which makes up about 20–30% of the seminal volume, and at ejaculation drives semen into the urethra through the rhythmic contraction of its smooth muscle. It is palpable through the anterior rectal wall and has recently drawn attention as a principal male internal erogenous region (colloquially the P-spot or male G-spot).

Overview

The prostate is an accessory sex gland common to male mammals. In the adult human male it is described as a chestnut-shaped organ roughly 3 cm in vertical length, 4 cm transverse, 2 cm anteroposterior, and 15–20 g in weight. Its form is an inverted cone, its base abutting the bladder neck and its apex directed toward the pelvic floor. The urethra (prostatic part) pierces its centre, and the paired ejaculatory ducts open into it.

The subjects it presents for medical study are wide-ranging. Embryology, histological structure (glandular epithelium and fibromuscular stroma), biochemistry centred on prostate-specific antigen (PSA), the composition and function of prostatic fluid, its role in the ejaculatory mechanism, benign prostatic hyperplasia (BPH) with age, prostate carcinoma, and prostatitis: it holds a long accumulation of scholarship as a research field where anatomy, histology, urologic oncology, and endocrinology cross.

In parallel, since the late twentieth century the fields of sexual medicine and sex education have advanced a movement to redescribe the prostate as a principal male internal erogenous region. The Ultimate Guide to Prostate Pleasure (2013) by Charlie Glickman and Aislinn Emirzian is a representative work that, on anatomical grounds, promotes sexual exploration of the region.

Etymology

The Latin prostata derives from Classical Greek prostátēs (“one who stands before,” “protector,” “leader”). In ancient Greek and Roman medicine the naming is attributed to the organ occupying a position “standing before” the bladder, and to its functioning as a “vanguard” of the testicles. English prostate directly inherits the Latin form. The Japanese loan-translation zenritsusen took root in the Meiji-period import of medicine, reconstructing the Greek sense (pro, “before” + stata, “stand”) in Sino-Japanese terms.

Anatomical structure

Position and zones

The prostate lies in the central lower part of the pelvic cavity, directly below the bladder neck. Posteriorly it abuts the anterior rectal wall, anteriorly the dorsal side of the pubic symphysis, and inferiorly it is fixed to the urogenital diaphragm. Between its posterior surface and the anterior rectal wall lies Denonvilliers’ fascia (fascia rectoprostatica), and this structure is the anatomical basis that makes palpation of the prostate by digital rectal examination possible.

Modern anatomy uses the zonal anatomy of John E. McNeal (1968) as the standard mode of description. On functional and histological criteria the prostate divides into four zones: the transition zone surrounding the periurethral region, the main site of BPH; the central zone, a conical zone surrounding the ejaculatory ducts, about 25% of the whole; the peripheral zone, the largest zone occupying the posterolateral part, where about 70–80% of prostate cancers arise; and the anterior fibromuscular stroma, a non-glandular fibromuscular layer occupying the front.

Histology

The prostatic parenchyma is a composite of glandular-epithelial and fibromuscular-stromal components. The glandular epithelium forms branched periurethral ductal tubules, each opening independently into the prostatic urethra. The epithelial cells produce prostatic fluid, and the smooth-muscle layer of the stroma carries the expulsion mechanism at ejaculation. The fibromuscular stroma makes up nearly half the total weight of the prostate, and this gives the prostate its “firm chestnut” feel, the texture felt on digital rectal examination.

Vessels and nerves

Arterial supply is carried by the prostatic arterial group, branches of the inferior vesical and middle rectal arteries. Venous return passes through the prostatic venous plexus into the internal iliac venous system. This plexus also communicates with the deep dorsal vein of the penis, forming a relay point of the intrapelvic venous system. The innervating nerves are autonomic fibres from the inferior hypogastric plexus, passing through the neurovascular bundle that runs over the prostatic capsule. This bundle is also part of the nerve pathway controlling penile erection, and is valued as a preservation target in prostate-cancer surgery.

Function

Secretion of prostatic fluid

The prostate, together with the seminal-vesicle and bulbourethral fluids, produces the secretion that constitutes semen. Prostatic fluid makes up about 20–30% of total seminal volume, milky-white and weakly acidic (pH about 6.5). Its principal components include citrate (an energy substrate contributing to sperm motility), zinc ions (antibacterial and sperm-stabilising), prostate-specific antigen (PSA, a serine protease responsible for the post-ejaculatory liquefaction of coagulated semen), prostatic acid phosphatase (PAP), and spermine (the chief cause of semen’s characteristic odour). These components contribute to the survival, motility, and fertilising capacity of sperm.

The ejaculatory mechanism

Ejaculation is described as a two-stage mechanism. In the emission phase, rhythmic contraction of the vas deferens, seminal vesicles, and prostatic smooth muscle collects semen in the prostatic urethra. In the expulsion phase, rhythmic contraction of the bulbospongiosus and ischiocavernosus muscles around the urethra drives semen out of the body. The prostate plays a central role in both stages. Contraction of the prostatic smooth muscle in the emission phase is described as an important component of the male sense of climax, and the phenomenon in which direct stimulation of the prostate itself is perceived as an “internal climax” is closely related to this physiological circuit.

Position as an erogenous region

Palpation through the anterior rectal wall

The prostate is the only male internal genital organ palpable through the anterior rectal wall. With a finger inserted through the anus, it is confirmed at about 5–8 cm as an elastic, chestnut-shaped structure beyond the wall. Sustained pressure and friction on this region can produce high sexual pleasure accompanied by deep pressure sensation. In medicine the digital rectal examination (DRE) aims at disease screening through palpation, but the same anatomical access route is also the physical basis of prostate stimulation as an erogenous region.

Positioning as the male G-spot

The sensation obtained by prostate stimulation is often described as a sustained pleasure dominated by deep pressure, qualitatively different from the sensation derived from direct stimulation of the glans of the penis. From a response pattern resembling stimulation of the G-spot region in women, the English-speaking world came to use the colloquial terms P-spot and male G-spot. Embryologically too, the female Skene’s glands (periurethral glands, the homologous tissue of a female prostate) and the male prostate stand in the relation of homologous organs derived from a single primordium, so there is anatomical ground for describing the G-spot and the prostate as “homologous erogenous regions.”

The response pattern to stimulation varies greatly between individuals, distributed from those who obtain clear sexual pleasure to those of poor sensitivity and those who report only discomfort. The folk belief of “a high-sensitivity region universally present in all men” is not medically supported, and careful description grounded in anatomical diversity is required. citation needed

Sex toys and “prostate massage”

Sex toys (adult toys) intended for prostate stimulation have rapidly developed in recent years as an independent product category. The basic form applies pressure to the prostate region with a tip curved through the anus toward the anterior rectal wall, and many electric types with vibration and rotation functions exist. The hands-free form represented by the Aneros products (originating from the High Island Health prostate massager of the late 1990s) established the industry standard. The term “prostate massage” was originally a medical term for a treatment technique for chronic prostatitis (a physician compresses the prostate at DRE to expel retained secretion); from the late twentieth century it generalised to mean prostate stimulation in sexual contexts.

Health-related topics

Benign prostatic hyperplasia

BPH is a benign disease in which the cells of the transition zone proliferate with age and the whole prostate enlarges. Histological enlargement is confirmed in about half of men over 50 and in over 80% of those over 80, a high-frequency condition close to an ageing phenomenon. The enlarged prostate compresses the urethra, producing lower urinary tract symptoms (LUTS) such as frequency, residual-urine sensation, weak stream, and nocturia. Drug therapy (α1-blockers, 5α-reductase inhibitors) is first-line; for severe cases, surgical intervention such as transurethral resection (TURP) is chosen.

Prostate cancer

Prostate cancer ranks high in male cancer mortality in Western countries, and in Japan its incidence and mortality have risen in recent years with the Westernisation of diet. Most are adenocarcinomas arising in the peripheral zone, asymptomatic in the early stage, with PSA screening the standard route of early detection. In the advanced stage it readily involves bone metastasis, treated by combinations of endocrine therapy (androgen deprivation), radiotherapy, surgery, and chemotherapy. After radical prostatectomy, preservation of sexual function (sparing of the neurovascular bundle) becomes a principal concern of postoperative quality of life.

Prostatitis

Prostatitis classifies into acute bacterial, chronic bacterial, chronic pelvic pain syndrome, and asymptomatic inflammatory types. The relation between prostate stimulation by sexual activity and onset is not clearly established, but there is continuing debate over conditions involving chronic tension of the pelvic floor muscles and circulatory stasis.

Thematisation in sexual expression and sexual culture

Straight context

In adult expression for heterosexuals, prostate stimulation was long positioned as a peripheral theme. “Pegging” (a woman penetrating a man with a strap-on dildo), which depicts the male recipient as an object of sexual pleasure, established itself as an independent genre comparatively recently; the genre thematises a heterosexual man actively developing the anal and prostate regions as erogenous zones. In Japanese-language adult expression too, independent subgenres are forming: scenes in which a female performer stimulates the male anal region, prostate-massage scenes as medical role-play, and the like.

Gay context

In male homosexual culture, prostate stimulation has been explicitly thematised from early on as a principal source of pleasure in anal acts. The description that grounds the sexual pleasure of the receptive side (bottom) in penetrative acts anatomically in sustained stimulation of the prostate region has been a standard component of gay sex education and expression since the latter half of the twentieth century. The anatomical and practical knowledge about prostate stimulation that set out from the gay community flowed gradually into heterosexual culture across the turn of the twenty-first century, and in part prompted an update of general awareness of male bodily sensation.

Cultural discourse

Discourse depicting the prostate region as “the hidden erogenous zone of the male body” took part, in parallel with body criticism since the second wave of feminism, in a movement to expand the description of male sensation. Against the traditional discourse that “male climax converges on penile ejaculation,” a discourse describing prostate-derived climax (prostate orgasm) as a sexual response on a separate axis is being assembled in parallel across sex education, sexual medicine, and sexual expression.

Relation to ageing

The prostate is one of the organs in which age-related change appears most markedly. Histologically it develops rapidly at puberty under androgen action, peaks in development in the twenties and thirties, and then enters a slow enlargement process. From the fifties the prevalence of BPH rises exponentially, and in old age the great majority of men show histological enlargement. Cancer incidence too depends strongly on age: autopsy studies report that about 60% of men over 80 show latent prostate cancer (cancer that does not become clinically manifest). In relation to sexual function, the functional activity of the prostate declines slowly with age, with each index, ejaculate volume, PSA value, and prostatic-fluid composition, changing accordingly as part of the normal ageing process.

See also

• Anal
• Koumon (anus)
• Inkei (penis)
• Kitou (glans)
• Adult toys