Prostate

Prostata

Also known as: prostate gland

A walnut-sized fibromuscular gland (≈20 g) surrounding the prostatic urethra below the bladder that adds a thin, milky, PSA- and citrate-rich secretion (≈20–30 % of semen); it is the site of benign prostatic hyperplasia and prostate cancer.

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Overview

Dimensions≈4 × 3 × 2 cm

Mass≈20 g (young adult)

Contribution to semen≈20–30 % of volume

Prostatic urethra≈3–4 cm long

The prostate is an inverted cone about 4 cm wide, 3 cm high and 2 cm deep. Its base abuts the bladder neck; its apex rests on the external urethral sphincter and perineal membrane; its anterior surface lies behind the pubic symphysis, separated by the retropubic space with the prostatic venous plexus; its posterior surface — flat, with a palpable median sulcus — faces the rectum across the rectovesical (Denonvilliers) fascia, which is why it can be examined by digital rectal examination. Its inferolateral surfaces rest on levator ani. It is enclosed in a fibrous capsule and an outer fascial sheath, with the venous plexus between them.

It contains 30–50 compound tubuloalveolar glands embedded in a dense fibromuscular stroma of smooth muscle and collagen; their ducts open into the prostatic urethra. Clinically it is described by McNeal zones: the peripheral zone (≈70 % of glandular tissue, posterior and lateral — origin of most carcinomas), the central zone (≈25 %, a wedge around the ejaculatory ducts), the transition zone (≈5 %, around the proximal urethra — site of BPH), and the non-glandular anterior fibromuscular stroma. Older anatomical texts use lobes (anterior, middle, two lateral, posterior).

The secretion is thin, milky and slightly acidic (pH ≈6.5); it contains prostate-specific antigen (PSA) — a kallikrein serine protease that liquefies the semen coagulum within 15–30 minutes — plus citrate, zinc (antibacterial), acid phosphatase, spermine and prostaglandins. During emission, sympathetically mediated contraction of the stroma (α1A receptors) expels it.

Location: Subperitoneal, in the lesser pelvis between the bladder neck (above) and the external urethral sphincter/perineal membrane (below), behind the pubic symphysis and in front of the rectum.

Parts & subdivisions

Peripheral zone (≈70 %)
Posterolateral; palpable on DRE; origin of ≈70 % of carcinomas; site of prostatitis.
Central zone (≈25 %)
Surrounds the ejaculatory ducts at the base.
Transition zone (≈5 %)
Around the proximal prostatic urethra; enlarges in BPH.
Anterior fibromuscular stroma
Non-glandular, continuous with the bladder neck and external sphincter.
Prostatic urethra
Passes vertically through the gland (≈3–4 cm); seminal colliculus on its posterior wall bears the ejaculatory duct openings and prostatic utricle.

Anatomy

Innervation: Prostatic plexus (from the inferior hypogastric plexus): sympathetic (contraction during emission) and parasympathetic (secretion). The cavernous nerves to the penis run in the neurovascular bundles posterolateral to the gland — at risk in radical prostatectomy (erectile dysfunction).
Arterial supply: Prostatic branches of the inferior vesical artery, with contributions from the internal pudendal and middle rectal arteries (all from the internal iliac).
Venous drainage: Prostatic venous plexus (receiving the deep dorsal vein of the penis) → internal iliac veins; it also communicates with the valveless vertebral venous (Batson) plexus — a route for prostate cancer to reach the lumbar spine and pelvis.
Lymphatic drainage: Mainly internal iliac and obturator nodes, also sacral and external iliac nodes.
Relations: Superior: bladder neck and seminal vesicles. Inferior: external urethral sphincter, perineal membrane. Anterior: pubic symphysis, retropubic space and puboprostatic ligaments. Posterior: ampullae of the ductus deferens, rectum (Denonvilliers fascia). Lateral: levator ani (levator prostatae).
Histology: Tubuloalveolar glands with folded mucosa lined by luminal columnar secretory cells and a basal-cell layer (absent in carcinoma), embedded in fibromuscular stroma; lamellated corpora amylacea (prostatic concretions) accumulate with age.
Development: Endodermal buds from the urogenital sinus (prostatic urethra), DHT-dependent; surrounding mesenchyme forms the stroma.

Function

Secretes ≈20–30 % of semen volume (PSA, citrate, zinc, acid phosphatase).
PSA liquefies the semen coagulum, freeing sperm.
Smooth muscle helps expel semen during emission and contributes to bladder-neck closure.
Converts testosterone to DHT locally (5α-reductase type 2).

Clinical significance

Benign prostatic hyperplasia

Transition-zone nodular hyperplasia in older men causing lower urinary tract symptoms and retention; smooth, enlarged gland on DRE; α1-blockers, 5α-reductase inhibitors, TURP.

Prostate cancer

Adenocarcinoma, mostly peripheral zone; hard irregular nodule; raised PSA; MRI and biopsy; Gleason/ISUP grading; osteoblastic bone metastases; androgen deprivation for advanced disease.

Prostatitis

Acute bacterial prostatitis (usually E. coli): fever, perineal pain, dysuria, exquisitely tender boggy prostate (avoid vigorous massage). Chronic prostatitis/chronic pelvic pain syndrome is commoner and usually non-bacterial.

PSA

Organ- not cancer-specific: raised by cancer, BPH, prostatitis, urinary retention, catheterisation and recent ejaculation; lowered by 5α-reductase inhibitors.

Mnemonics

Zones

Peripheral = Palpable, Prostate cancer; Transition = Too big (BPH).

Compiled from standard anatomy and physiology references — see the Reproductive System sources. For education only; not medical advice.