What is the pampiniform plexus and why is it important? What clinical emergency arises when it twists?
tap to flip
Answer
Pampiniform plexus = web of veins wrapping around the testicular artery. Acts as a countercurrent heat exchanger to cool arterial blood before it reaches the testis (spermatogenesis needs ~2°C below core body temp).
Testicular torsion: twisting of spermatic cord → cuts off arterial supply → ischemia. Surgical emergency — must be untwisted within 6 hours to save the testis. Presentation: acute severe unilateral scrotal pain, high-riding testis, absent cremasteric reflex, "bell-clapper" deformity.
Varicocele: dilation of pampiniform plexus ("bag of worms"), more common on left (left gonadal vein → left renal vein at 90°).
Leydig Cells
Where are Leydig cells located? What do they produce and under what stimulation? Histologic markers?
tap to flip
Answer
Location: In the interstitium BETWEEN seminiferous tubules (not inside the tubules).
Products:Testosterone (main) + a small amount of DHT. Stimulated by LH from anterior pituitary.
Testosterone maintains: spermatogenesis, accessory glands (prostate, seminal vesicles, bulbourethral), male secondary sex characteristics, libido.
Histo markers:Lipid droplets, smooth ER, mitochondria with tubular cristae, Reinke crystals (pathognomonic).
DHT = 50× more potent than testosterone (binds androgen receptor with higher affinity).
Sertoli Cells & Blood-Testis Barrier
Where are Sertoli cells located? What forms the blood-testis barrier and why is it essential?
tap to flip
Answer
Location: INSIDE the seminiferous tubules, resting on the basement membrane. Stimulated by FSH.
Why it matters: 1. Separates immune-privileged meiotic cells from circulation (meiosis begins post-puberty — cells are "foreign" to immune system). 2. Meiotic cells rely on Sertoli cells for nutrients.
Also: secrete inhibin B (neg feedback on FSH), MIS/AMH (fetal), ABP (concentrates testosterone).
Spermatogenesis — Cell Progression
Trace the germ cell progression from base to lumen of the seminiferous tubule. Which step is the only mitotic division?
tap to flip
Answer
Germ cells move from basement membrane → lumen as they mature:
1. Spermatogonia (2n) — divide by MITOSIS (only mitotic step) — sit on basement membrane. 2. Primary spermatocytes (4n) — enter meiosis I. 3. Secondary spermatocytes (2n) — complete meiosis II. 4. Spermatids (n) — begin spermiogenesis (morphologic transformation). 5. Spermatozoa (n) — mature sperm released into lumen.
Process takes ~74 days. Synchronous divisions via incomplete cytokinesis (cytoplasmic bridges) ensure continuous sperm supply.
HPG Axis (Male)
Trace the hypothalamic-pituitary-gonadal axis in males. Which hormone targets Leydig vs. Sertoli cells? Where does each feedback signal act?
tap to flip
Answer
Hypothalamus: GnRH → ant. pituitary Ant. pituitary (basophils of pars distalis): • LH → Leydig cells → testosterone ("LH → Leydig") • FSH → Sertoli cells → support germ cells + ABP + inhibin B ("FSH → Follicle/Sertoli")
Feedback: • Testosterone → negative feedback on hypothalamus (GnRH) AND pituitary (LH) • Inhibin B → selective negative feedback on FSH only
Clinically: ↑FSH + normal T = Sertoli dysfunction (↓ inhibin B); ↑LH + ↓T = Leydig dysfunction.
Spermiogenesis
What is spermiogenesis (vs. spermatogenesis)? Name the four parts of the mature sperm structure.
tap to flip
Answer
Spermiogenesis = final morphologic transformation of round spermatid → elongated spermatozoon (subset of spermatogenesis). No cell division.
Key events:acrosome forms (hydrolytic enzymes for zona pellucida penetration), nucleus condenses, flagellum (axoneme) forms, mitochondria coil around midpiece, residual cytoplasm discarded.
Mature sperm structure: • Head: nucleus + acrosome • Mid-piece: axoneme (9+2 microtubules) + mitochondrial sheath (ATP for flagellar motility) • Principal piece: axoneme + fibrous sheath • End piece: axoneme + plasma membrane only
Excurrent Ducts — Order
Trace the path of sperm from seminiferous tubule to urethra. Which two ducts are intratesticular?
Structure: ~20 small tubules leaving rete testis → coalesce into head of epididymis. Give the duct a characteristic "scalloped/uneven lumen" on histology.
What epithelium lines the vas deferens? What are the wall's distinguishing features? What is vasectomy?
tap to flip
Answer
Epithelium:Pseudostratified columnar with stereocilia (same as epididymis).
Wall:3 THICK smooth muscle layers (inner longitudinal, middle circular, outer longitudinal) — provide powerful peristaltic propulsion during ejaculation. This is how to distinguish vas from epididymis histologically (vas has much thicker muscular wall).
Vasectomy: surgical cut/ligation of vas deferens → prevents sperm from reaching ejaculate. Sperm are still made in testis but reabsorbed. Testosterone and ejaculate volume unaffected (sperm are <5% of semen volume).
Embryology: Wolffian duct (SEED).
Seminal Vesicles
What do seminal vesicles secrete? What percentage of ejaculate do they contribute? Are sperm stored here?
tap to flip
Answer
Histo: Simple or pseudostratified columnar epithelium; highly folded mucosa for ↑ surface area.
SPERM ARE NOT STORED HERE — common exam trap! Sperm are stored in the tail of the epididymis. SV fluid joins sperm at the ejaculatory duct.
Prostate
What lines the prostate? What are corpora amylacea? What is PSA and its clinical use?
tap to flip
Answer
Histo: Simple or pseudostratified columnar epithelium. Unique to mammals. Contains the verumontanum — landmark where ejaculatory duct meets prostatic urethra.
Corpora amylacea = small, round calcified bodies in prostatic glandular lumens. Classic histologic feature of the prostate. Increase with age.
PSA (prostate-specific antigen): serine protease secreted by prostatic epithelium. Liquefies semen coagulum after ejaculation. Leaks into blood when prostatic architecture disturbed → ↑ serum PSA = marker of BPH, prostatitis, or prostate cancer.
Clinical: Prostate cancer is the most common cancer in men (3rd deadliest). Hormone-sensitive → treated with androgen deprivation therapy.
Bulbourethral (Cowper's) Glands
Where are Cowper's glands located, what do they secrete, and what is the distinguishing histologic clue?
tap to flip
Answer
Location: At the base of the penis; secrete into the proximal penile (spongy) urethra. Paired glands.
Secretion: Alkaline mucin (pre-ejaculate fluid) — two roles: (1) protects urethra from urine acidity; (2) shields sperm from damaging enzymes (residual acrosomal proteases).
Histologic clue: the gland is surrounded by SKELETAL MUSCLE — the only accessory gland like this — because it sits within the urogenital diaphragm (external urethral sphincter).
Name the paired and unpaired erectile tissues of the penis. Which one surrounds the urethra? What covers them?
tap to flip
Answer
Corpus cavernosum — PAIRED dorsal erectile bodies; fill with blood during erection, surrounded by tunica albuginea (dense CT). Compression against tunica during engorgement causes rigidity.
Corpus spongiosum — UNPAIRED ventral body; SURROUNDS the urethra. Expands distally as the glans penis. Less rigid during erection (doesn't compress urethra — allows ejaculation).
Penis parts: Root (fixed, attached to body wall) · Body (shaft, with dartos muscle) · Glans (expanded tip) · Prepuce (foreskin) covers glans.
3. Penile (spongy) urethra — longest; runs through corpus spongiosum. Lined by pseudostratified/stratified columnar, transitions to stratified squamous at the glans (navicular fossa).
From outermost to innermost, the three testis coverings are: the visceral tunica ___________ (single layer of mesothelial cells), the tunica ___________ (thickest, dense CT), and the tunica ___________ (loose CT with vasculature).
Hint: The thickest CT layer carries a Latin name meaning "white tunic."
FIB 02 — Leydig vs Sertoli
___________ cells sit in the INTERSTITIUM between seminiferous tubules and secrete testosterone under ___________ (gonadotropin) stimulation. ___________ cells sit INSIDE the tubules on the basement membrane and support germ cells under ___________ (gonadotropin) stimulation.
Hint: "LH → Leydig; FSH → Follicle/Sertoli."
FIB 03 — Blood-Testis Barrier
The blood-testis barrier is formed by ___________ junctions between adjacent ___________ cells. It divides the seminiferous tubule into a ___________ compartment (containing spermatogonia) and an ___________ compartment (containing meiotic germ cells).
Hint: Protects meiotic germ cells from immune exposure.
FIB 04 — Spermatogenesis Order
Spermatogenic cells from basement membrane to lumen: ___________ (2n) → primary ___________ (4n) → secondary spermatocytes (2n) → ___________ (n) → spermatozoa. Only the first step is ___________ (mitosis/meiosis).
Hint: Takes about 74 days; synchronous divisions via incomplete cytokinesis.
FIB 05 — Sperm Structure
The sperm head contains the ___________ (enzymes for egg penetration) + condensed nucleus. The mid-piece houses the axoneme (9+2 microtubules) surrounded by a ___________ sheath (ATP production). During spermiogenesis, spermatids transform into ___________.
FIB 06 — Excurrent Pathway
Sperm exit the seminiferous tubule via the tubulus ___________, enter the ___________ testis (embedded in mediastinum), pass through ~20 ___________ ductules that reabsorb fluid, then enter the ___________ for maturation + storage.
FIB 07 — Epididymis & Vas Histology
Both the epididymis and vas deferens are lined by ___________ columnar epithelium with ___________ (long non-motile microvilli). The vas has a much thicker wall due to ___________ layers of smooth muscle.
Hint: These are NOT true motile cilia — they're structural only.
FIB 08 — Seminal Vesicles
Seminal vesicles contribute about ___________ % of ejaculate volume. They secrete ___________ (sugar for sperm energy), alkaline fluid, prostaglandins, and clotting proteins. Importantly, sperm are ___________ stored here.
Hint: Fructose assay is used clinically to check seminal vesicle patency.
FIB 09 — Prostate Histology
The prostate contains small round calcified bodies called ___________ in the glandular lumens. Prostate epithelium secretes ___________ (a serine protease) that liquefies semen; blood levels are used to screen for prostate ___________ and BPH.
Hint: The rounded calcifications in prostatic glands are sometimes called "prostatic concretions."
FIB 10 — Urethra Epithelium
The prostatic urethra is lined by ___________ epithelium (same as bladder). The membranous and most of the penile urethra are lined by ___________ columnar epithelium. At the distal glans (navicular fossa), it transitions to stratified ___________.
Hint: Transitional → columnar → squamous as you move distally.
Instructions: Drag and drop the items into the correct order, then click "Check Order." Use "Show Answer" if you get stuck.
Haploid (n); undergo spermiogenesis into spermatozoa
Forms blood-testis barrier; secretes ABP, MIS, inhibin B
Diploid stem cells (2n); only germ cells to undergo mitosis
Score: 0/5 correct
Set 3 — Accessory Gland → Key Product/Histologic Feature
Match each male accessory gland to its signature secretion or histologic clue.
Gland
Seminal vesicles
Prostate
Bulbourethral (Cowper's) glands
Epididymis (tail)
Seminiferous tubule (Sertoli)
Key Product / Histo Clue
Primary site of sperm storage + final maturation
Fructose (sperm energy); alkaline fluid; 70% of ejaculate; NO sperm stored
Produces inhibin B + androgen-binding protein (ABP); blood-testis barrier
PSA secretion; corpora amylacea in glandular lumens
Mucin secretion; surrounded by SKELETAL muscle
Score: 0/5 correct
Test Trap Mode: Each statement is either TRUE or FALSE as written. Many are designed to catch common exam errors. Click T or F — then read the explanation carefully.
Trap 01 — Leydig vs Sertoli Location
"Leydig cells are located inside the seminiferous tubules, while Sertoli cells sit in the interstitium between tubules."
FALSE. Reversed. Sertoli cells are INSIDE the seminiferous tubules (on the basement membrane) and surround developing germ cells. Leydig cells are in the INTERSTITIUM between tubules. Mnemonic: "LEydig = in Exterior; Sertoli = Sitting among sperm." LH → Leydig (→ testosterone); FSH → Sertoli (→ ABP, inhibin B, germ cell support).
Trap 02 — Which Germ Cell Does Mitosis?
"Primary spermatocytes undergo mitosis to maintain the germ cell pool throughout life."
FALSE.Spermatogonia (not spermatocytes) are the ONLY germ cells that undergo mitosis. They are the stem cells on the basement membrane, dividing into Type A (self-renewal) + Type B (committed) daughters. Primary spermatocytes undergo MEIOSIS I. Secondary spermatocytes undergo MEIOSIS II. Spermatids undergo spermiogenesis (no division). Memorize: gonia = mitosis; cytes = meiosis; tids = morphologic shaping.
Trap 03 — Blood-Testis Barrier
"The blood-testis barrier is formed by tight junctions between Leydig cells, separating spermatogonia from immune-sensitive cells."
FALSE. The blood-testis barrier is formed by tight junctions between SERTOLI cells (not Leydig). It divides the seminiferous tubule into the basal compartment (spermatogonia) and adluminal compartment (meiotic spermatocytes + spermatids). The barrier protects MEIOTIC and post-meiotic cells — which express novel antigens — from circulating immune cells. Damage (e.g., trauma, vasectomy reversal) can cause anti-sperm antibodies → immunologic infertility.
Trap 04 — Seminal Vesicle Storage
"Seminal vesicles are the primary storage site of mature sperm before ejaculation."
FALSE.SPERM ARE NOT STORED IN SEMINAL VESICLES — classic exam trap! The seminal vesicles produce fluid (fructose, prostaglandins, ~70% of ejaculate volume) that joins sperm at the ejaculatory duct. Sperm are stored in the TAIL of the epididymis (up to ~1 month). The name "seminal vesicle" is misleading — it refers to their secretory role in semen, not storage.
Trap 05 — Pampiniform Plexus
"The pampiniform plexus is an arterial network that warms blood flowing to the testis to optimize sperm production."
FALSE. Two errors: it's a VENOUS plexus (not arterial), and it COOLS (not warms) blood. The pampiniform plexus is a web of veins wrapping around the testicular artery, functioning as a countercurrent heat exchanger to keep testicular temperature ~2°C below core body. Spermatogenesis is heat-sensitive. Clinically: dilation of the plexus = varicocele ("bag of worms," usually left-sided) → infertility. Twisting = testicular torsion, a surgical emergency.
Trap 06 — Cilia vs Stereocilia
"The pseudostratified epithelium of the epididymis has motile cilia that propel sperm toward the vas deferens."
FALSE. The epididymis (and vas deferens) have STEREOCILIA, NOT true motile cilia. Stereocilia are long, non-motile microvilli — purely structural (↑ surface area for fluid reabsorption, sperm maturation). Sperm are propelled by smooth muscle contractions of the ductal wall. True motile cilia exist in the efferent ductules and rete testis — but those use dynein-driven 9+2 microtubules for actual movement. Don't confuse the two: stereo = structure, cilia = motion.
Trap 07 — Bulbourethral Surroundings
"The bulbourethral (Cowper's) glands are surrounded by smooth muscle, distinguishing them from other accessory glands."
FALSE. The bulbourethral glands are surrounded by SKELETAL muscle, not smooth muscle — this is their histologic pathognomonic feature. They sit within the urogenital diaphragm (external urethral sphincter = skeletal). Function: secrete alkaline mucin (pre-ejaculate) that (1) neutralizes residual urine acidity in the urethra and (2) protects sperm from damaging acrosomal enzymes. Female homolog: Bartholin (greater vestibular) glands.
Trap 08 — DHT Potency
"Testosterone binds the androgen receptor more potently than DHT — that's why testosterone is the dominant circulating androgen."
FALSE. Reversed. DHT binds the androgen receptor with ~50× higher affinity than testosterone (DHT is the more potent androgen). Testosterone is the main CIRCULATING androgen (higher serum levels) because most tissues convert it to DHT locally via 5α-reductase. Drugs like finasteride (5α-reductase inhibitor) reduce DHT production specifically — used for BPH and androgenetic alopecia. Defective androgen receptor = Complete Androgen Insensitivity Syndrome (CAIS).
Spermatogenesis — Full Cellular Progression
Stage
Ploidy
Location
Key Event
Spermatogonium (type A/B)
2n
Basal compartment (basement membrane)
ONLY germ cell to undergo MITOSIS; stem cell renewal
Primary spermatocyte
4n
Crosses blood-testis barrier into adluminal compartment
Enters MEIOSIS I (prolonged prophase I); largest germ cell
Secondary spermatocyte
2n
Adluminal compartment
Completes MEIOSIS II quickly (rarely seen on histology)
Released (spermiation); still immature — gains motility in epididymis
Total duration: ~74 days per cycle + another ~2 weeks for epididymal maturation. Synchronous waves via incomplete cytokinesis ensure continuous sperm supply.
Male Reproductive Tract — Epithelium Summary
Structure
Epithelium
Step 1 Hook
Seminiferous tubules
Stratified germinal + Sertoli cells
Blood-testis barrier via Sertoli tight junctions
Tubulus rectus
Simple cuboidal
Intratesticular; straight exit from seminiferous tubule
Key principle: "LH → Leydig → testosterone" and "FSH → Sertoli → inhibin B + germ cell support" is the foundation of male endocrinology. Dysfunction of Sertoli cells selectively ↑ FSH (↓ inhibin); Leydig dysfunction selectively ↑ LH (↓ testosterone). Peripheral testosterone → DHT via 5α-reductase for external genital/prostate effects.