Instructions: Select the single best answer for each question. Review your answers at the end of the block before proceeding.
Question 1 of 5 — Blood-Testis Barrier
A 34-year-old man presents to a fertility clinic with his wife after 3 years of unsuccessful conception attempts. History reveals a testicular trauma (falling from a ladder onto fence railing) 6 years ago. Testicular biopsy shows normal spermatogenesis but laboratory analysis reveals circulating anti-sperm antibodies. Which histologic structure — when disrupted — most likely produced this finding?
C — Blood-testis barrier via Sertoli tight junctions. The blood-testis barrier is formed by tight junctions between adjacent Sertoli cells, separating seminiferous tubules into basal compartment (spermatogonia) and adluminal compartment (meiotic + post-meiotic cells). Meiotic cells begin dividing at puberty — AFTER the immune system has been educated to recognize "self" — so they express novel antigens that would be seen as foreign. The barrier prevents exposure. Trauma (or vasectomy reversal) can breach the barrier → immune system develops anti-sperm antibodies → impaired fertility even if spermatogenesis itself is normal. This is an important cause of immunologic male infertility.
Question 2 of 5 — Leydig vs Sertoli Cell Identity
On routine testicular histology, a pathologist identifies two cell populations. Cell population A is located INSIDE the seminiferous tubules, extends from basement membrane to lumen, and embraces developing germ cells at all stages. Cell population B is located in the INTERSTITIUM between tubules, contains abundant lipid droplets, smooth ER, and mitochondria with tubular cristae. Which gonadotropin primarily stimulates Cell population B, and what is its main product?
AFSH; inhibin B
BFSH; androgen-binding protein (ABP)
CLH; testosterone
DACTH; cortisol
EGnRH; androstenedione
C — LH; testosterone. Cell population A describes Sertoli cells (INSIDE tubules; form blood-testis barrier; FSH-stimulated → produce ABP, inhibin B, MIS). Cell population B describes Leydig cells (INTERSTITIAL; lipid droplets, smooth ER, tubular cristae = hallmarks of steroidogenic cells; LH-stimulated → produce testosterone + a small amount of DHT). Mnemonic: "LH → Leydig; FSH → Follicle/Sertoli". Pathognomonic Leydig feature: Reinke crystals. DHT (50× more potent than T) is the main androgen acting on external male genitalia and prostate.
Question 3 of 5 — Spermatogenesis Mitosis vs Meiosis
A medical student studying germ cell progression in the testis asks which cells undergo mitosis vs meiosis. A senior histology faculty responds that only ONE type of germ cell maintains the ability to undergo MITOSIS, and this cell type sits on the basement membrane as a renewable stem population. Which cell is this, and what is its ploidy?
ASpermatogonium (2n)
BPrimary spermatocyte (4n)
CSecondary spermatocyte (2n)
DSpermatid (n)
ESpermatozoon (n)
A — Spermatogonium (2n).Spermatogonia are the stem cells of the male germ line, located on the basement membrane of the seminiferous tubule. They are diploid (2n) and undergo MITOSIS throughout adult life — Type A daughters remain as stem cells for self-renewal; Type B daughters commit to differentiation and become primary spermatocytes. From there, MEIOSIS begins: primary spermatocytes (4n → 2n after meiosis I) → secondary spermatocytes (2n → n after meiosis II, rapidly) → round spermatids (n). Spermatids don't divide — they undergo spermiogenesis (morphologic transformation into spermatozoa with acrosome, flagellum, mitochondrial sheath). Entire cycle: ~74 days.
Question 4 of 5 — Acrosome Function
A researcher studying fertilization observes that a mature sperm penetrating the zona pellucida releases proteolytic enzymes in a localized burst at its anterior head. Which of the following best describes the structure and function involved, and what is its developmental origin?
AMitochondrial sheath; generates ATP for flagellar motility; derived from mitochondrial biogenesis
BAcrosome (modified lysosome-like vesicle) containing hyaluronidase, acrosin, and other hydrolytic enzymes; derived from the Golgi apparatus during spermiogenesis
CFibrous sheath; structural support of the principal piece; derived from centrosome
DCentriole; organizes axoneme; derived from proximal microtubule organizing center
EZona pellucida glycoproteins; released from oocyte surface during fertilization
B — Acrosome. The acrosome is a modified lysosome-like cap covering the anterior half of the sperm nucleus. It is formed during spermiogenesis from the Golgi apparatus. Contents include hyaluronidase (digests hyaluronic acid in the corona radiata), acrosin (serine protease — digests zona pellucida glycoproteins), and other hydrolytic enzymes. On contact with the zona pellucida's ZP3 receptor, the acrosome reaction releases these enzymes → sperm penetration → fertilization. Sperm structure review: Head (acrosome + nucleus) · Mid-piece (axoneme + mitochondrial sheath) · Principal piece (axoneme + fibrous sheath) · End piece (axoneme + plasma membrane).
Question 5 of 5 — Pampiniform Plexus & Temperature
A 19-year-old athlete who habitually uses hot tubs, wears tight briefs, and keeps his laptop on his lap presents with secondary infertility. Semen analysis shows reduced sperm motility and count. His serum testosterone and gonadotropins are normal. Which of the following anatomic structures fails in this scenario, and why is this clinically important?
ASertoli-Sertoli tight junctions; immune disruption of germ cells
BPampiniform plexus countercurrent cooling; spermatogenesis requires ~2°C below core body temperature
CBlood-testis barrier; prevents systemic exposure to sperm antigens
DAcrosome formation; Golgi dysfunction during spermiogenesis
ETunica albuginea; mechanical compression during erection
B — Pampiniform plexus cooling failure. The pampiniform plexus is a web of veins wrapping around the testicular artery, functioning as a countercurrent heat exchanger to cool arterial blood before it reaches the testis. Testicular temperature is maintained ~2°C below core body temp — critical for spermatogenesis. Chronic heat exposure (hot tubs, tight underwear, laptops, occupational heat, fever) degrades sperm production → oligospermia, asthenospermia. Varicocele is the pathologic dilation of this plexus → loss of cooling → infertility (#1 treatable male infertility cause). Intervention: avoidance of heat sources; varicocele ligation/embolization if identified. Spermatogenesis recovers over ~3 months (one full cycle) after heat removal.
Block 2 — Excurrent Ducts & Accessory Glands
5 questions · Epididymis, vas, seminal vesicles, prostate, urethra
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07:30
Block Timer
Instructions: Select the single best answer for each question. Review your answers at the end of the block before proceeding.
Question 6 of 15 — Epididymis Histology
A pathologist examines a section from the male excurrent ductal system. The epithelium is pseudostratified columnar with tall apical projections that look like microvilli but are much longer. Immunohistochemistry confirms these projections are NOT motile (they lack dynein). Surrounding smooth muscle is thin (single circular layer). Which structure is this, and what do the apical projections do?
ARete testis; intratesticular channel network
BEfferent ductules; ciliated + resorptive cells
CEpididymis; stereocilia for surface area (sperm maturation)
DVas deferens; cilia for propulsion
ESeminal vesicle; cilia for fluid mixing
C — Epididymis with STEREOCILIA. The epididymis is lined by pseudostratified columnar epithelium with long stereocilia — non-motile microvilli (NOT true motile cilia, despite the confusing name). Function: increase surface area for fluid reabsorption and sperm maturation. Smooth muscle is THIN (single layer) in the epididymis, distinguishing it from the vas deferens which has 3 THICK muscle layers. Sperm propulsion happens via smooth muscle contractions, not cilia. Sperm mature during their ~2-week transit and are stored in the tail. Both epididymis and vas deferens are Wolffian duct derivatives with stereocilia; you distinguish them by wall thickness.
Question 7 of 15 — Vas Deferens & Vasectomy
A 34-year-old man with 2 children elects to undergo vasectomy. He returns 4 months postoperatively with a repeat semen analysis showing azoospermia. He reports normal libido and sexual function. Which of the following best describes the expected physiologic profile after vasectomy?
A↓ testosterone, ↓ ejaculate volume by ~50%, ↓ libido
EUnchanged testosterone, complete absence of ejaculate
C — All unchanged except sperm absence.Vasectomy transects the vas deferens — sperm can no longer enter the ejaculate. Because sperm are only ~5% of ejaculate volume, the ejaculate volume is essentially unchanged. Seminal vesicles (70%) and prostate (25%) contribute the bulk of volume; those ducts are unaffected. Testosterone is unchanged because Leydig cells are intact and blood flow preserved — libido and sexual function are normal. Sperm are still produced in the testis but get reabsorbed or phagocytosed in the epididymis. Risk of anti-sperm antibody formation due to breach of the blood-testis barrier — this is why vasectomy reversal often fails to restore fertility even after surgical reconnection.
Question 8 of 15 — Prostate Zones
A 67-year-old man presents with urinary frequency, nocturia, weak stream, and hesitancy. Digital rectal examination reveals a symmetrically enlarged, smooth, rubbery prostate. PSA is 3.8 ng/mL (mildly elevated for age). Which anatomic zone of the prostate is MOST affected, and which treatment MOST directly targets the pathogenesis?
B — Transitional (periurethral) zone; finasteride targets DHT.BPH affects the TRANSITIONAL (periurethral/central) zone of the prostate — this zone surrounds the urethra, so hyperplasia obstructs urine flow. Driven by DHT (formed from T via 5α-reductase). Finasteride blocks this conversion → shrinks the gland over 3–6 months. Symmetric smooth enlargement on DRE. PSA mildly ↑. Contrast with prostate cancer, which arises in the PERIPHERAL (posterior) zone (palpable as hard nodules) — would warrant biopsy + radical prostatectomy/radiation/ADT. First-line for BPH symptoms is also α1-blocker (tamsulosin) for quick relief by smooth-muscle relaxation.
Question 9 of 15 — Cowper's Gland Identification
A histology slide shows a paired exocrine gland with simple columnar epithelium secreting mucus. The glands are surrounded by a thick layer of SKELETAL muscle, distinguishing them from nearby glandular structures. Location clues: the glands sit at the base of the penis near the urogenital diaphragm. Which structure is this, and what is its primary function?
ASeminal vesicles; fructose production
BProstate gland; PSA secretion
CBulbourethral (Cowper's) glands; alkaline mucin to protect urethra + shield sperm from acidic urine residues and acrosomal enzymes
DGlands of Littré; urethral lubrication
ESkene glands; female-specific
C — Bulbourethral (Cowper's) glands. The pathognomonic histologic feature of bulbourethral glands is being surrounded by SKELETAL muscle — no other male accessory gland has this. Cowper's glands sit within the urogenital diaphragm, which is composed of skeletal muscle (external urethral sphincter). Function: secrete alkaline mucin pre-ejaculate that (1) neutralizes residual urine acidity in the urethra and (2) protects sperm from acrosomal proteases that may damage them during transit. Female homolog: Bartholin (greater vestibular) glands. Seminal vesicles have simple/pseudostratified columnar with highly folded mucosa (not skeletal muscle surround). Prostate has corpora amylacea + smooth muscle stroma.
Question 10 of 15 — Urethra Epithelial Transitions
A forensic pathologist examines the male urethra microscopically along its full length. Four distinct epithelial zones are identified: Zone 1 (proximal, near bladder) is lined by one type; Zone 2 (through the external urethral sphincter) and Zone 3 (most of the penis length) share a different epithelium; Zone 4 (at the tip of the glans, the navicular fossa) transitions to yet another type. Which of the following correctly pairs each zone with its epithelium?
AZone 1: transitional (urothelium); Zones 2-3: pseudostratified/stratified columnar; Zone 4: stratified squamous
BZone 1: stratified squamous; Zones 2-3: simple cuboidal; Zone 4: transitional
CZone 1: simple columnar; Zones 2-3: pseudostratified; Zone 4: simple cuboidal
DAll four zones are lined by transitional epithelium
EZone 1: keratinized squamous; Zones 2-3: columnar; Zone 4: non-keratinized squamous
A — Transitional → columnar → squamous. The male urethra has 3 anatomic segments with epithelial transitions:
• Prostatic urethra: transitional (urothelium) — same epithelium as the bladder it continues from. Site of the verumontanum + ejaculatory duct openings. • Membranous urethra: pseudostratified/stratified columnar. Shortest segment; passes through the urogenital diaphragm (external urethral sphincter — skeletal muscle = voluntary continence). • Penile (spongy) urethra: pseudostratified/stratified columnar for most of its length, transitioning to stratified squamous at the navicular fossa (distal glans, where continuous with skin of glans penis).
Pattern: transitional → columnar → squamous as you move distally.
Block 3 — Male Repro Pathology & Clinical Correlates
5 questions · Torsion, testicular CA, BPH, prostate CA, ED pharmacology
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07:30
Block Timer
Instructions: Select the single best answer for each question. These questions integrate male reproductive histology with clinical pathology.
Question 11 of 15 — Klinefelter Hormone Pattern
A 22-year-old tall thin man presents to a fertility clinic with his wife after 2 years of unsuccessful conception. On exam, he has gynecomastia, small firm testes bilaterally, a eunuchoid habitus, and mild intellectual disability. Labs: testosterone 180 ng/dL (low), LH 36 mIU/mL (elevated), FSH 52 mIU/mL (markedly elevated), estradiol 65 pg/mL (elevated). Semen analysis shows azoospermia. Which karyotype is most likely, and what underlying defect explains the elevated FSH?
C47 XXY (Klinefelter); seminiferous tubule dysgenesis → ↓ inhibin B → loss of FSH negative feedback
D45 XO (Turner); streak ovaries with absent sex steroids
E46 XY; Kallmann syndrome with absent GnRH
C — Klinefelter (47 XXY). Buzzwords: tall eunuchoid, gynecomastia, small firm testes, azoospermia, ↑↑ FSH > ↑ LH with ↓ T + ↑ estradiol. Pathophysiology: extra X chromosome causes seminiferous tubule dysgenesis during puberty → loss of germ cells + Sertoli cell dysfunction → ↓ inhibin B → removes feedback → ↑↑ FSH. Leydig cells are also impaired → ↓ T → ↑ LH. Residual T is peripherally aromatized → ↑ estradiol → gynecomastia. Most common genetic cause of male infertility; ↑ risk for breast cancer, extragonadal germ cell tumors, autoimmune disease. Kallmann (E) would show ↓ LH/FSH (hypogonadotropic) + anosmia. CAIS (B) is 46 XY but phenotypically female.
Question 12 of 15 — Seminoma — "Fried-Egg" Cells
A 30-year-old man notices a painless firm mass in his right testis. Scrotal US confirms a hypoechoic intratesticular lesion. Tumor markers: β-hCG 25 mIU/mL (slightly elevated), AFP NORMAL, LDH 680 U/L, PLAP elevated. Radical inguinal orchiectomy reveals tumor composed of uniform cells with clear cytoplasm and large central nuclei ("fried-egg cells") arranged in sheets separated by fibrous septa infiltrated with lymphocytes. Which of the following statements about this tumor is correct?
AIt is a non-seminomatous germ cell tumor requiring aggressive BEP chemotherapy
BIt is a pure seminoma; highly radiosensitive with excellent 5-year survival; AFP is NEVER elevated in pure seminoma
CIt is a yolk sac tumor; Schiller-Duval bodies expected
DIt is a Leydig cell tumor; would cause Cushingoid features
EIt is a lymphoma; managed with CHOP chemotherapy alone
B — Pure seminoma. Classic histology: "fried-egg" cells (large clear cells with central nuclei) in sheets separated by fibrous septa + lymphocytic infiltrate. AFP is NEVER elevated in pure seminoma — if it were, this would be a mixed/non-seminomatous GCT. β-hCG may be slightly elevated (from syncytiotrophoblast-like cells in ~15%), LDH reflects tumor burden, PLAP is often elevated. Seminomas are extraordinarily radiosensitive and chemosensitive → excellent prognosis even with metastasis. Tx options: inguinal orchiectomy + surveillance (stage I) / retroperitoneal radiation / single-agent carboplatin. NSGCTs (embryonal, yolk sac, choriocarcinoma, teratoma) require BEP (bleomycin, etoposide, cisplatin) chemo for most stages. Risk factors: cryptorchidism (↑ 4–6× even after orchiopexy), Klinefelter, family Hx, contralateral testicular CA.
Question 13 of 15 — Prostate Cancer Metastasis
A 72-year-old man presents with 6 weeks of worsening low back pain and a recent fall. PSA is 76 ng/mL. DRE reveals a hard nodule on the posterior prostate. Plain film of the lumbar spine shows sclerotic lesions in multiple vertebrae. Alkaline phosphatase is 480 U/L (elevated). Which of the following best characterizes his metastatic disease, and why is this pattern distinctive?
AOsteolytic (lytic) bone mets with hypercalcemia; characteristic of breast + lung + kidney cancers
BOsteoblastic (sclerotic, bone-forming) mets; prostate cancer uniquely promotes osteoblast activity → ↑ alk phos; bone mets cause pain/pathologic fractures
CMixed lytic-blastic lesions indistinguishable from other cancers
DPure lymphatic spread with no bone involvement
EPrimary bone tumor arising independently in the spine
B — Osteoblastic bone mets. Prostate adenocarcinoma arises in the peripheral (posterior) zone (palpable as hard nodule on DRE). Metastases distinctively cause OSTEOBLASTIC (sclerotic) lesions — NOT osteolytic — by secreting factors that stimulate osteoblast activity (endothelin-1, BMPs). This manifests as: • Bone pain (especially axial skeleton: pelvis, lumbar spine, femur, ribs) • ↑ alkaline phosphatase (marker of bone formation) • Sclerotic lesions on X-ray/CT/bone scan (dense, white appearance) • Pathologic fractures; epidural cord compression (oncologic emergency)
Question 14 of 15 — Sildenafil + Nitrates Interaction
A 62-year-old man with stable angina on daily isosorbide mononitrate presents to the ED 90 minutes after taking his friend's sildenafil for ED. He is hypotensive (BP 68/38), tachycardic (HR 110), and nearly syncopal. Which of the following molecular mechanisms best explains this hemodynamic catastrophe?
BNitrates release NO → activate guanylyl cyclase → ↑ cGMP; sildenafil is a PDE5 inhibitor that prevents cGMP breakdown → synergistic cGMP accumulation → profound systemic vasodilation
CBoth drugs are direct β-adrenergic agonists → tachycardia with hypotension
DSildenafil metabolizes nitroglycerin into a toxic vasodilator
EAdditive anticoagulant effect causes unrecognized GI hemorrhage
B — Synergistic cGMP accumulation. Normal erection physiology: parasympathetic S2-S4 ("Point") → NO release from cavernous nerves → guanylyl cyclase → ↑ cGMP in corpora cavernosa smooth muscle → relaxation → engorgement. Nitrates (nitroglycerin, isosorbide) elevate cGMP systemically via the same NO-GC pathway for coronary vasodilation. PDE5 inhibitors (sildenafil, tadalafil, vardenafil) block the enzyme that breaks down cGMP, sustaining elevation. Combined use → massive cGMP accumulation → profound systemic vasodilation → severe hypotension, reflex tachycardia, syncope, MI, and potentially death. ABSOLUTE contraindication. Separate doses by at least 24h (sildenafil, shorter t½) or 48h (tadalafil, longer t½). Treat acute hypotension with IV fluids + phenylephrine (α1 agonist). Also caution with α1-blockers (tamsulosin) due to additive hypotension.
Question 15 of 15 — Comprehensive Male Infertility
A 32-year-old man presents with his wife after 2 years of unsuccessful conception. His history includes testicular trauma from a bicycle accident at age 12 and occasional marijuana use. Physical exam reveals a left-sided "bag of worms" scrotal swelling that enlarges with Valsalva and decompresses when supine. Testicular volumes are slightly reduced bilaterally (14 mL each). Labs: testosterone 320 ng/dL (borderline), LH 6 mIU/mL (normal), FSH 12 mIU/mL (mildly elevated), inhibin B borderline low. Semen: count 8 million/mL (low), motility 22% (low), morphology 3% normal. Which intervention would MOST directly address his primary reproductive problem?
ADiscontinue marijuana and repeat semen analysis in 3 months only
BSurgical ligation or embolization of the left varicocele, which impairs testicular cooling and causes oligoasthenoteratospermia — the most common treatable cause of male infertility
CBegin testosterone replacement therapy to improve sperm production
DKaryotype analysis + empiric BEP chemotherapy
EStart sildenafil for ED-related infertility
B — Varicocele repair. Classic varicocele presentation: "bag of worms" scrotal swelling, Valsalva-responsive, decompresses supine, LEFT-sided (left gonadal vein → left renal vein at 90°). Causes impaired testicular cooling → oligoasthenoteratospermia (↓ count + ↓ motility + ↓ morphology) — the classic semen profile. Mildly elevated FSH + low-normal inhibin B reflects early Sertoli dysfunction from heat stress. Varicocele is the MOST COMMON treatable cause of male infertility. Treatment: surgical ligation or percutaneous embolization → improves semen parameters in 60–70% + pregnancy rates. Other points: (A) good advice but not primary cause; (C) testosterone replacement WORSENS fertility — it suppresses LH/FSH via feedback → less intratesticular testosterone → ↓ spermatogenesis (common clinical error); (D) no indication without azoospermia and suspected germ cell tumor; (E) no ED implied.
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