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)