Physiology chapters
Male reproductive physiology
How the hypothalamus, pituitary and testes control male reproduction, what testosterone and DHT do before birth and after puberty, how sperm are made, and how male hormones change with age.
- GnRH (pulsatile) → LH acts on Leydig cells (testosterone) and FSH acts on Sertoli cells (spermatogenesis); testosterone feeds back on LH, inhibin on FSH.
- Before birth, testosterone forms the internal male organs (Wolffian ducts) and DHT forms the external genitalia and prostate; AMH from Sertoli cells removes the Müllerian ducts.
- Spermatogenesis takes about 64–74 days, needs a temperature a few degrees below body temperature, and is protected by the blood-testis barrier.
On this page
Overview
The testes have two jobs: making sperm (in the seminiferous tubules) and making testosterone (in the interstitial tissue).
Both are controlled by the hypothalamic-pituitary-gonadal axis.
For the cell stages of sperm production, see also gametogenesis.
The hypothalamic-pituitary-gonadal axis
- The hypothalamus releases GnRH in pulses (about every 1–3 hours).
- GnRH stimulates the anterior pituitary to release LH and FSH.
- LH acts on Leydig cells → testosterone.
- FSH acts on Sertoli cells → supports spermatogenesis, makes androgen-binding protein and inhibin.
- Testosterone feeds back on the hypothalamus and pituitary to reduce GnRH and LH.
- Inhibin feeds back on the pituitary to reduce FSH.
LH → Leydig → testosterone (feedback by testosterone). FSH → Sertoli → sperm and inhibin (feedback by inhibin).
Spermatogenesis needs both FSH and high local testosterone in the tubules. Androgen-binding protein from Sertoli cells keeps testosterone concentrated there.
Giving external testosterone (anabolic steroids) suppresses LH, so the testes make less testosterone locally and sperm production falls, causing small testes and infertility.
Testosterone and DHT
Testosterone is made by Leydig cells from cholesterol. In many target tissues it is converted by 5α-reductase to the more potent dihydrotestosterone (DHT).
Prenatal effects
| Hormone | Source | Effect in the male fetus |
|---|---|---|
| Anti-Müllerian hormone (AMH) | Sertoli cells | Regression of the Müllerian ducts (no uterus or uterine tubes) |
| Testosterone | Leydig cells (stimulated by hCG from the placenta early on) | Develops the Wolffian ducts into the epididymis, vas deferens and seminal vesicles |
| DHT | From testosterone by 5α-reductase | Forms the penis, scrotum and prostate (external genitalia) |
Testosterone also helps the testes descend into the scrotum in the last months of pregnancy.
Testosterone builds the internal male ducts; DHT builds the external genitalia and prostate.
Effects after puberty
- Growth of the penis, scrotum and testes.
- Deepening of the voice (larynx enlarges).
- Body hair in a male pattern; beard; male-pattern baldness (DHT) in those predisposed.
- Acne (sebaceous glands, DHT).
- Increased muscle mass and protein synthesis (anabolic).
- Bone growth and density; eventually closure of the epiphyses (partly after conversion to oestrogen).
- Increased red cell production.
- Libido and spermatogenesis.
- Prostate growth (DHT).
Finasteride blocks 5α-reductase and is used for benign prostatic hyperplasia and male-pattern baldness.
Spermatogenesis
Spermatogenesis happens in the seminiferous tubules from puberty onwards.
- Spermatogonia (at the base of the tubule) divide by mitosis.
- Some become primary spermatocytes, which enter meiosis I.
- Secondary spermatocytes (haploid) complete meiosis II.
- Spermatids change shape into sperm (spermiogenesis).
The whole process takes about 64–74 days. Sperm then mature in the epididymis (gaining motility over about two weeks) and gain the ability to fertilise (capacitation) in the female tract.
Sertoli cells
- Nurse and support the developing cells.
- Form the blood-testis barrier with tight junctions between neighbouring Sertoli cells. This protects developing sperm (which carry new antigens) from the immune system and from toxins.
- Make AMH (fetus), androgen-binding protein, inhibin, and fluid.
Temperature
Spermatogenesis needs a temperature about 2–3°C below core body temperature. The scrotum keeps the testes cool (the pampiniform venous plexus acts as a heat exchanger).
Undescended testes (cryptorchidism) are too warm, so they produce few sperm and have a higher cancer risk. Leydig cells keep working, so testosterone is usually normal.
Clinical relevance
Androgen insensitivity syndrome
How it happens: defective androgen receptors in a 46,XY person.
What you see: female external genitalia, a short blind vagina, no uterus (AMH works), testes in the abdomen or groin; testosterone and LH are high.
5α-reductase deficiency
How it happens: DHT cannot be made.
What you see: ambiguous or female-appearing external genitalia at birth; virilisation at puberty when testosterone rises.
Klinefelter syndrome (47,XXY)
What you see: small firm testes, infertility, tall stature, gynaecomastia; low testosterone, high LH and FSH, low inhibin.
Expect: the targets of LH and FSH, feedback by testosterone and inhibin, the prenatal roles of AMH, testosterone and DHT, 5α-reductase and finasteride, the steps and duration of spermatogenesis, Sertoli cell functions and the blood-testis barrier, temperature, and hormone changes with age.
Quick revision
- GnRH pulses → LH (Leydig, testosterone) and FSH (Sertoli, sperm, inhibin).
- Testosterone inhibits LH; inhibin inhibits FSH.
- Fetus: AMH removes Müllerian ducts; testosterone builds Wolffian ducts; DHT builds external genitalia and prostate.
- Spermatogenesis about 64–74 days; needs FSH, high local testosterone and cool testes.
- Blood-testis barrier: Sertoli cell tight junctions.
- Testosterone falls slowly with age; LH and FSH rise.
Written by The House Job from standard physiology references (Guyton and Hall Textbook of Medical Physiology; BRS Physiology).
FAQ
What do LH and FSH do in the male?
LH stimulates Leydig cells to make testosterone; FSH acts on Sertoli cells to support sperm production and inhibin release.
What is the role of DHT in the fetus?
It causes the external genitalia and prostate to develop in the male pattern.
What forms the blood-testis barrier?
Tight junctions between adjacent Sertoli cells.
How long does spermatogenesis take?
About 64 to 74 days.