Histology of Seminal Vesicles, Prostate Gland, and Penis

Prostate Gland – Low-Power Overview

• Oval organ encased in a fibromuscular capsule.

• Landmarks to recognise at scanning magnification:
  • \textbf{Urethra} – large, centrally placed lumen.
  • \textbf{Prostatic utricle} – thin midline out-pouching behind urethra; embryological remnant of paramesonephric duct.
  • \textbf{Ejaculatory ducts} – paired, slit-like lumina joining the urethra posteriorly; lined by simple / pseudostratified columnar epithelium.
  • \textbf{Glandular tissue} – profuse, tubulo-alveolar acini arranged concentrically around urethra.
  • \textbf{Anterior fibromuscular stroma} – dense smooth muscle + collagen; paucity of glands.
  • \textbf{Capsule} – thick fibro-elastic tissue with abundant smooth muscle fibres; sends septa inward.

• Zonal anatomy (clinically mirrors imaging and pathology):

  1. \text{Anterior fibromuscular zone (AFM)} – non-glandular; contributes to urethral tone.

  2. \text{Peripheral zone (PZ)} – makes up ~70\% of volume; main (true) glands; commonest site of carcinoma.

  3. \text{Central zone (CZ)} – surrounds ejaculatory ducts; thick epithelium; relative carcinoma-resistance.

  4. \text{Transitional zone (TZ)} – surrounds urethra; contains mucosal + submucosal glands; primary site of benign prostatic hyperplasia (BPH).

Prostate Gland – Classification of Glands

• All prostatic acini are tubulo-alveolar but differ by depth, size and duct system.

1. Mucosal (Inner Peri-urethral) Glands

• Essentially short epithelial invaginations of the prostatic urethra.

• Ducts open directly into urethral lumen.

• Duct epithelium grades:
  • Deep portion – tall columnar.
  • Near urethra – cuboidal → transitional (urothelium).

• Responsible for early stages of BPH nodules in TZ.

2. Submucosal Glands

• Tubulo-alveolar, irregular, with wide lumina.

• Widely spaced secretory tubules exhibit alveolar out-pouchings.

• Lined by simple cuboidal or columnar epithelium; height varies with androgenic influence (↓ atrophy after castration, ↑ hyperplasia with age).

• Lumina often contain \textbf{corpora amylacea} – concentric, eosinophilic, glycoprotein–rich precipitates that calcify with age; appear as “oxyphilic masses” (Quiz Q8).

3. Main (Peripheral) Glands

• Largest, most numerous; elaborate folding of epithelium → saw-tooth profile.

• Excretory duct + acinus form continuous duct–acinar system lined by pseudostratified columnar epithelium.

• Stroma between acini packed with smooth muscle bundles activated by sympathetic outflow during ejaculation.

Prostate – High-Power Details

• Secretory units show two epithelial layers:
  • \textbf{Luminal cells} – tall columnar with apical secretory granules (citric acid, PSA, PAP, fibrinolysin, zinc).
  • \textbf{Basal cells} – cuboidal, regenerative stem-cell population; express p63/CK5 (important in immunohistochemistry to rule out carcinoma which loses basal layer).

• Surrounding inter-acinar stroma:
  • Fibroblasts and myofibroblasts.
  • Abundant smooth muscle (contracts to expel prostatic fluid).
  • Autonomic nerves and lymphatics (route of metastasis).
  • Collagen type I + III.

Prostate – Summary Exercise (Slide 16)

• Region A vs B to classify as mucosal, submucosal or peripheral:
  • Assess distance from urethra, size of lumen, epithelial height and amount of surrounding smooth muscle.
  • Peripheral (main) glands → large folded acini, abundant corpora amylacea, dense muscular stroma.
  • Submucosal → medium-sized irregular lumina, closer to urethra, fewer folds.
  • Mucosal → smallest, directly abutting urethral urothelium.

Seminal Vesicle – Gross Architecture

• Each vesicle = single, highly coiled, unbranched tubular gland (~15\,\text{cm} stretched length; 5\,\text{cm} folded).

• Wall layers (external → internal):

  1. \textbf{Adventitia} – loose areolar connective tissue anchoring to bladder/rectum; sends connective-tissue septa between lobules.

  2. \textbf{Muscularis} – two smooth muscle coats:
     • Inner circular.
     • Outer longitudinal.
     Contraction empties gland during emission.

  3. \textbf{Mucosa} – forms profuse primary, secondary and tertiary folds, giving luminal cross-section a stellate/“honey-comb” appearance.

Seminal Vesicle – High-Power Features

• Epithelium: pseudostratified columnar with two cell types:
  • Principal columnar cells – apical cytoplasm packed with secretory granules (fructose, prostaglandins, coagulating proteins); numerous lipid droplets → foamy look under H & E.
  • Basal cells – small, round nuclei along basement membrane; progenitor pool.

• Lamina propria: loose fibroelastic tissue, capillaries and occasional smooth muscle fibers (core of mucosal folds).

• Muscularis externa under LP – thick, easily seen, helps distinguish from prostate.

• Hormonal responsiveness: testosterone/estradiol regulate epithelial height; atrophy post-orchiectomy.

Penis – Cross-Sectional Histology

• Three cylindrical masses of erectile tissue enclosed by \textbf{Buck’s fascia} (deep fascia of penis):

  1. \textbf{Corpora cavernosa (paired, dorsal)} – each surrounded by dense fibroelastic \textbf{tunica albuginea}; tunica fuses in midline to create \textbf{pectiniform (pectinate) septum}.

  2. \textbf{Corpus spongiosum (ventral)} – smaller, surrounds penile (spongy) urethra; tunica thinner allowing urethral patency during erection.

• Vascular components:
  • Helicine arteries – thick-walled branches that empty into cavernous sinusoids.
  • Dorsal arteries, veins and nerves located dorsally outside tunica.

• Surface covered by thin skin lacking adipose; loose subcutaneous (dartos) fascia contains superficial dorsal vessels.

Practical / Real-World Connections

• Zonal anatomy is crucial in radiology (multiparametric MRI) and targeted prostate biopsies.

• Corpora amylacea and loss of basal cell layer help pathologists differentiate benign glands from adenocarcinoma.

• BPH nodules (mucosal + submucosal) obstruct urethra → lower urinary tract symptoms → TURP specimens show scant peripheral glands.

• Seminal vesicle secretion (~70\% of semen volume) provides fructose energy source for sperm motility; absence lowers fertility.

• Penile erection depends on relaxation of trabecular smooth muscle and engorgement of cavernous sinusoids; phosphodiesterase-5 inhibitors maintain cGMP to sustain this.

Ethical / Philosophical Notes

• Age-related prostate changes raise screening dilemmas (PSA vs over-diagnosis).

• Surgical removal of seminal vesicles during radical prostatectomy can affect fertility and ejaculation – requires informed consent.

Numerical / Statistical References

• Peripheral zone accounts for \approx 70\% of gland volume and >75\% of prostatic carcinomas.

• Transitional zone makes up \approx 5\% of glandular tissue in young males but expands dramatically with BPH.

Quiz Pointers (Pages 14–15)

1. Identify organ 1–4:
   • Assess epithelial type, presence of corpora amylacea, muscularis thickness, mucosal folding.

2. Bladder slides – recognise umbrella cells (large, binucleate, scalloped apical membrane with uroplakins; plaques + hinge regions allow stretching).

3. Muscularis propria of bladder: interlacing smooth muscle bundles (detrusor); skeletal muscle only at external urethral sphincter.

4. Orientation of muscle fibres determined by viewing elongated vs circular profiles of smooth muscle nuclei.

5. Adventitia vs serosa: superior bladder (dome) covered by peritoneum → serosa; remainder retroperitoneal → adventitia.

6. Corpora amylacea = laminated glycoprotein concretions in prostatic acini (Q8).

7. Slide 16 A & B: rely on acinar size and location to designate mucosal / submucosal / peripheral.

8. Provide three concise justifications for each diagnosis in Slide 22 (epithelium type, gland pattern, stromal clues).

Study Tips & Mnemonics

• “M-S-P” (Mucosal, Submucosal, Peripheral) radiating outward from urethra.

• Seminal vesicle looks like “spongy Swiss-roll” under low power – wildly folded lumen with thin intervening muscle.

• Penile cross-section: remember ‘2 Dorsal, 1 Ventral’ (two CC, one CS).