HUBS3511 · Human Reproduction And Pregnancy
The Male Reproductive System
The male reproductive system is a continuous, steady-state factory: from puberty onward the testis runs flat-out, making billions of sperm over a lifetime and a roughly constant level of testosterone — nothing here surges or arrests. In HUBS3511 every fact reduces to one of two jobs: manufacture the gamete (spermatogenesis, inside the seminiferous tubule) or regulate and deliver it (the HPG axis and the duct system). The short-answer marks live in the mechanisms — the sperm pathway in order, the Sertoli–vs–Leydig split, the ploidy ladder of spermatogenesis, why the male axis has no LH surge, and how SRY flips the bipotential gonad to a testis while the female pathway runs as the default. Get the two cell types and the two-layer feedback straight and the chapter falls out.
What this chapter covers
- 011.1 Testis & duct anatomy and the sperm pathway in order
- 02Scrotal thermoregulation: dartos vs cremaster, 2-3 °C below core
- 031.2 The seminiferous tubule: Sertoli (FSH) vs Leydig (LH) cells
- 04The blood–testis barrier and ABP
- 051.3 Spermatogenesis: the 2n→n ladder, one cell → four sperm
- 06Spermatogenesis vs spermiogenesis (reshaping, no division)
- 071.4 The male HPG axis: all negative feedback, no surge
- 081.5 Sex determination: SRY, AMH, testosterone, DHT and the default pathway
Worked example: tracing the sperm pathway and naming the cell types
- +1(a) Start where sperm are made: the seminiferous tubules of the testis.
- +2(a) The collecting route: seminiferous tubules → rete testis → efferent ductules → epididymis (maturation & storage) → ductus (vas) deferens → ejaculatory duct → urethra → out.
- +1(a) Flag the maturation site: sperm gain motility and zona-binding ability in the epididymis, NOT in the testis — a guaranteed mark.
- +1(b) FSH → Sertoli cells (inside the tubule): nurse cells that form the blood–testis barrier and secrete ABP, inhibin and (in the fetus) AMH.
- +1(b) LH → Leydig cells (between the tubules): the endocrine cells that make testosterone.
Key terms
- Seminiferous tubule
- The coiled tube inside the testis where sperm are made. Stem cells (spermatogonia) sit at the basement-membrane periphery and mature toward the lumen; the most mature cells lie at the lumen.
- Sertoli cell
- The FSH-driven “nurse” cell inside the tubule. It supports developing sperm, forms the blood–testis barrier with tight junctions, and secretes androgen-binding protein (ABP), inhibin and (in the fetus) anti-Müllerian hormone.
- Leydig cell
- The LH-driven endocrine cell in the interstitium between the tubules. It synthesises testosterone, which is held high locally by ABP to sustain spermatogenesis.
- Spermiogenesis
- The final, non-dividing step of spermatogenesis: a round spermatid is reshaped into a spermatozoon — building the acrosome, condensing the nucleus and growing the flagellum and mitochondrial midpiece. No cell division occurs.
- SRY
- The sex-determining region on the Y chromosome: the master switch that turns the bipotential gonad into a testis. Without SRY the gonad becomes an ovary by default.
The Male Reproductive System FAQ
Why does the male HPG axis have no LH surge?
Because there is no positive-feedback step in the male axis — testosterone and inhibin only ever inhibit. Testosterone suppresses the hypothalamus and pituitary, and inhibin selectively suppresses FSH, so the system self-stabilises into a steady state. The LH surge requires the oestrogen positive-feedback switch that only the female axis has.
What is the difference between spermatogenesis and spermiogenesis?
Spermatogenesis is the whole process — mitosis to maintain the stem pool, then two meiotic divisions, then reshaping. Spermiogenesis is only the final reshaping of a spermatid into a sperm (acrosome, tail, midpiece) with no cell division. Mixing the two up is a classic short-answer error.
Where do sperm mature — the testis or the epididymis?
Sperm are made in the seminiferous tubules but gain motility and zona-binding ability in the epididymis. “Matured in the testis” is wrong, and is a common trap.
Why is the female pathway called the default?
Because the basic embryo develops as female unless SRY is present. SRY → testis → Sertoli make AMH (Müllerian duct regresses) and Leydig make testosterone (Wolffian duct persists), with DHT masculinising the external genitalia. With no SRY, none of that happens and the female tract forms without needing a positive “ovary-determining” signal.
Exam move
Memorise the sperm pathway as one unbroken sequence and rehearse it cold — it is the most reliable mark in the chapter. Then lock the two pairings with their mnemonics: FSH→Sertoli (support, barrier, inhibin) and LH→Leydig (testosterone), with inhibin suppressing FSH only. For spermatogenesis, be able to draw the ladder with ploidy labelled (2n→n) and the 1→4 outcome, and keep spermatogenesis (the whole process) distinct from spermiogenesis (reshaping, no division). For the axis, the one-line answer to “why no surge” is “no positive-feedback step”. For sex determination, keep the ducts paired (testosterone keeps Wolffian, AMH destroys Müllerian, DHT masculinises external) and state that female is the default.
