Histology – Prostate, Seminal Vesicles, Penis & Urethra

Lower urinary tract (clinical “LUT”) = urinary bladder + urethra; symptoms involve bladder, sphincter, urethra & (in men) prostate
Male tract components (cranio-caudal): ureter → urinary bladder → ductus deferens → prostatic urethra → penis (penile urethra) → testis, scrotum, seminal vesicle, prostate, rectum, bulbourethral (Cowper) gland, epididymis

Musculo-glandular organ located inferior to bladder, traversed by prostatic urethra & ejaculatory ducts
Secretion: thin, opalescent, slightly acidic fluid containing enzymes (diastase, proteases, fibrinolysin) & citric acid
Largest male accessory gland
Progressive enlargement begins ≈ 45\,\text{yrs}, marked in elderly

Capsule: dense connective tissue (CT) rich in smooth muscle
Stroma: broad fibromuscular septa radiate to colliculus seminalis; rich in smooth muscle & elastic fibres; produces growth factors vital for normal & neoplastic growth

Mucosal (inner peri-urethral) glands
• Short invaginations of urethral epithelium; open directly into urethra
• Ducts: columnar → cuboidal → transitional near urethra
Submucosal (outer peri-urethral) glands
• Small, more numerous, tubulo-alveolar, open by short ducts
• Together with mucosal group form CENTRAL ZONE; separated from main glands by thick smooth muscle
Main (peripheral) glands
• 30\text{–}50 tubulo-alveolar glands empty via 15\text{–}30 long ducts lateral to colliculus
• Acini irregular; ducts lined by low columnar epithelium

Colliculus: urothelial elevation on posterior urethral wall; flanked by openings of ejaculatory ducts, utricle & prostatic ducts
Prostatic utricle: remnant of Müllerian ducts, located within colliculus; often distally dilated

Acini of main glands: folded tall columnar cells (foamy cytoplasm, pale basal nuclei) + small dark basal cells; epithelium varies (pseudostratified → cuboidal/flat) depending on testosterone level
Prostatic concretions (corpora amylacea)
• Concentric, lamellated, 20\,\mu m – 2\,mm, acidophilic
• Condensed glycoprotein/cholesterol around desquamated cell fragments; may calcify → calculi
• Number ↑ with age & duct obstruction

Luminal (secretory) cells
• Androgen dependent, produce PSA & acid phosphatase, limited stem capacity
Basal cells
• Androgen independent, stem-cell pool, resemble myoepithelial cells
Neuroendocrine cells (androgen-independent)
Rare stem cells
Surrounding stroma: fibroblasts, smooth muscle, nerves, lymphatics

Lobes (embryologic, clinically cited)

Zones (modern anatomy)

Peripheral Zone (PZ) – 65\%; posterolateral, majority glandular tissue; 75\text{–}85\% cancers
Central Zone (CZ) – 25\%; surrounds ejaculatory ducts, forms base; <5\% cancers (more aggressive, invade seminal vesicles)
Transition Zone (TZ) – 10\% in youth; surrounds urethra, grows with age; origin of BPH, \approx20\% cancers (less malignant)
Anterior fibromuscular stroma (AFS) – non-glandular

Benign prostatic hypertrophy (BPH): stromal + mucosal/submucosal gland hyperplasia; strangulates urethra
• Incidence: 40\% men at 50\,yrs, 95\% at 80\,yrs
Prostate carcinoma: adenocarcinoma arises from luminal cells, mostly PZ
PSA test: detects luminal cell product ↑ in Ca / inflammation
Stroma supplies growth factors driving both normal & cancer growth

Pair of elongated, highly coiled, unbranched tubular diverticula of vas deferens; posteroinferior to bladder
Merge with distal ductus deferens to form ejaculatory duct
Wall layers: adventitia (incomplete septa, loose CT), thick muscularis (inner circular + outer longitudinal SM), mucosa with multiple branching folds into lumen

Epithelium: pseudostratified columnar/cuboidal with basal cells; lipid droplets → foamy cytoplasm
Lamina propria: elastic CT extends into folds
Lumen: acidophilic secretory masses (fructose-rich)
Muscularis contracts during emission → ejects fluid into ejaculatory duct
Contributes up to 70\% of semen volume (NOT sperm reservoir)

Located in urogenital diaphragm at penile root
Compound tubulo-alveolar mucous glands; simple cuboidal/columnar epithelium
Secrete thick, slippery, alkaline fluid that lubricates urethra; first secretion after erection, precedes semen
Secretion protects urethral epithelium from urine acidity

Mucous glands along dorsal penile urethra; short & long types penetrating spongy body
Produce glycosaminoglycan-rich colloid secretion

Three erectile cylinders encased by common fascia & thin skin
• Paired corpora cavernosa (dorsal) enveloped by tunica albuginea; median pectinate septum
• Corpus spongiosum (ventral) surrounding urethra; thinner tunica
Erectile tissue: network of cavernous sinusoids lined by endothelium, separated by CT & smooth muscle trabeculae

Pre-prostatic (intramural) – \sim1\,cm; urothelium
Prostatic – 3\text{–}4\,cm; urothelium; receives ejaculatory, prostatic ducts & utricle at colliculus
Membranous – 1\,cm; passes external sphincter; pseudostratified columnar (no umbrella cells); narrowest part
Spongy/Penile – 15\text{–}16\,cm; in corpus spongiosum; proximal pseudostratified columnar, distal stratified squamous
• Subdivisions:
– Bulbar urethra (bulb): stratified/pseudostratified columnar
– Pendulous urethra (shaft): same epithelium
– Fossa navicularis (glans): non-keratinizing stratified squamous

Seminal vesicle: pseudostratified columnar; thin LP w/ elastic fibres; outer loose CT; muscularis inner circ + outer long
Prostate: simple/pseudostratified columnar; vascular CT w/ dense elastic net; smooth muscle interwoven
Bulbourethral: simple cuboidal → columnar; ducts pseudostratified; fibroelastic CT around glands; interstitial SM + skeletal fibres

Semen volume ≈ 3\,mL
• Seminal vesicles: major volume, fructose energy
• Prostate: enzymes activate sperm motility
• Bulbourethral: lubricating/alkaline pre-ejaculate
• Littre glands: minor mucus
• Sperm count: 2\times10^{8} – 3\times10^{8} spermatozoa
Sequence during ejaculation: Cowper fluid → prostatic fluid + sperm (from ampulla) → seminal vesicle fluid

TZ → BPH; PZ → carcinoma (75-85%)
CZ surrounds ejaculatory ducts at prostatic base
Luminal (secretory) cells secrete PSA; PSA test for Ca screening/monitoring due to leakage into blood
Stroma rich in smooth muscle; produces growth factors important in cancer
Bladder epithelium: relaxed – 5\text{–}6 layers, dome-shaped umbrella cells; distended – 2\text{–}3 layers, flattened umbrella cells
Accessory glands: seminal vesicle (≈70\% semen), prostate (≈25\%), bulbourethral & Littre (minor)
See urethra segment list above
Adenocarcinoma from luminal cells may leave basal layer intact or compressed; basal cells lack androgen receptors → relatively resistant
Bladder serosa covers superior surface & upper posterior wall; remainder adventitia
Muscularis propria = detrusor (inner long, middle circ, outer long SM)