Subjects and lessons to explore.

Law

Human Physiology II · Systems Physiology

Male Reproductive Physiology

6 min read
10 key termsReport an error
Want it in plain words first? Jump to Eli explains — the same idea, no jargon.
On this page 7 sections
  1. In 30 seconds
  2. Why this matters
  3. The college version
  4. Eli explains
  5. Worked example
  6. Key takeaway
  7. Study tools

In 30 seconds

The testes perform two jobs: sperm production in the and secretion by , with supporting and nourishing developing sperm. A single hypothalamic-pituitary-gonadal axis controls both: drives (which acts on Sertoli cells) and LH (which drives Leydig cells to make testosterone), and testosterone plus feed back to keep the system balanced. Erection is a parasympathetic, nitric-oxide-mediated vascular event, whereas ejaculation is a sympathetic reflex that expels semen.

Why this matters

Male reproductive physiology is assessed with measurements such as testosterone, FSH, LH, and inhibin B, plus semen analysis (sperm count, motility, and morphology). The HPG-axis pattern is diagnostic: primary testicular failure raises FSH/LH, whereas hypothalamic-pituitary failure lowers them — but reference ranges and interpretation criteria vary by institution and jurisdiction. These notes support education and do not replace clinical instruction; any concerning symptoms require evaluation by qualified clinicians.

The college version

1. Testicular anatomy separates sperm production from hormone production

The seminiferous tubules are coiled tubes where occurs, lined by Sertoli cells. Between the tubules, in the interstitial space, sit the Leydig cells, which secrete testosterone. This spatial separation lets one axis control two products.

2. Spermatogenesis converts stem cells into sperm

Spermatogonia divide and mature through spermatocytes (where meiosis occurs) and spermatids, which then differentiate (spermiogenesis) into mature spermatozoa. Sertoli cells provide structural support, nutrients, a blood-testis barrier, and androgen-binding protein, and they secrete inhibin.

3. The HPG axis uses dual feedback

Hypothalamic GnRH stimulates the anterior pituitary to release FSH and LH. FSH acts on Sertoli cells to support spermatogenesis and stimulate inhibin; LH acts on Leydig cells to stimulate testosterone. Testosterone feeds back to suppress GnRH and LH, while inhibin selectively suppresses FSH, fine-tuning sperm output.

How it works

  1. GnRH pulses drive the pituitary to release FSH and LH.
  2. LH makes Leydig cells secrete testosterone; FSH makes Sertoli cells support sperm development.
  3. Spermatogonia mature through meiosis and spermiogenesis into spermatozoa.
  4. Glands add fluids to make semen, which travels the epididymis and vas deferens.
  5. Testosterone and inhibin feed back to restrain GnRH, LH, and FSH.
  6. Parasympathetic NO produces erection; sympathetic signals drive ejaculation.

Common confusions

Do not confuseWithDifference
Leydig cellsSertoli cellsLeydig cells (interstitial) make testosterone; Sertoli cells (in tubules) support sperm and make inhibin
FSH actionLH actionFSH targets Sertoli cells; LH targets Leydig cells
ErectionEjaculationErection is parasympathetic/NO vasodilation; ejaculation is sympathetic muscle contraction
Testosterone feedbackInhibin feedbackTestosterone suppresses GnRH/LH; inhibin suppresses FSH

Memory aids

"S-L-F" — Sertoli cells are Supported by FSH, Leydig cells are Led by LH. For erection vs ejaculation, remember "Point and Shoot": Parasympathetic for the Point (erection), Sympathetic for the Shoot (ejaculation).

Quick review

Topic Recap

The testes house spermatogenesis in the seminiferous tubules (supported by Sertoli cells) and testosterone production in the Leydig cells. GnRH drives FSH and LH; FSH acts on Sertoli cells and LH on Leydig cells, while testosterone and inhibin provide feedback. Erection results from parasympathetic nitric-oxide vasodilation, and ejaculation from sympathetic contraction, completing the two branches of male reproductive function.

Knowledge Check

  1. Which cells produce testosterone, and which pituitary hormone stimulates them?
  2. What is the role of Sertoli cells in spermatogenesis, and which two products do they secrete or bind?
  3. What two hormones provide negative feedback on the HPG axis, and what does each inhibit?
  4. Why is erection described as a parasympathetic event, and which molecule is the key mediator?
  5. Which division of the autonomic nervous system drives ejaculation?

Answers and Rationales

  1. Leydig cells, stimulated by LH. FSH acts on Sertoli cells instead.
  2. Sertoli cells nourish developing sperm, form the blood-testis barrier, and secrete inhibin and androgen-binding protein, concentrating testosterone for spermatogenesis.
  3. Testosterone inhibits GnRH and LH; inhibin selectively inhibits FSH, allowing independent control of androgen levels and sperm output.
  4. Because parasympathetic nerves release nitric oxide, which activates cGMP and relaxes penile vascular smooth muscle to increase blood flow and produce erection.
  5. The sympathetic nervous system, which contracts the ducts and glands to move semen and trigger ejaculation.
Eli, the EliExplains learning guide

Eli explains

The same idea, in plain words

Explain it like I’m 10

Think of the testis as a factory with two departments. The "sperm department" (seminiferous tubules) is a long assembly line where immature cells divide and mature into sperm, with Sertoli cells as the support staff feeding and protecting them. The "hormone department" (Leydig cells) sits between the assembly lines and manufactures testosterone. A control room in the brain (hypothalamus and pituitary) sends two messengers — FSH to the support staff and LH to the hormone department — and reads reports (testosterone and inhibin) to decide how hard each department should work. The comparison stops being exact because the two departments depend on each other: testosterone from the Leydig cells is itself required for sperm to mature, so they are not as separate as two factory floors.

Simple Example

FSH is like the manager who tells the Sertoli support staff to keep the assembly line running, while LH tells the Leydig cells to keep making testosterone — and the finished product (testosterone) then reports back to slow the managers down when enough is made.

Worked example

  1. Central drive: The hypothalamus releases GnRH in pulses into the portal blood, driving the anterior pituitary to secrete FSH and LH.
  2. Leydig cell response: LH binds Leydig-cell receptors and raises cAMP, stimulating testosterone synthesis from cholesterol. Testosterone enters the blood and also diffuses into the tubules.
  3. Sertoli cell response: FSH (and testosterone) acts on Sertoli cells to support spermatogenesis. Sertoli cells concentrate testosterone via androgen-binding protein and create the blood-testis barrier that protects developing germ cells.
  4. Spermatogenesis: Spermatogonia undergo mitotic divisions, meiosis (reducing chromosome number to 23), and spermiogenesis (tail and acrosome formation), producing motile sperm that are released into the tubule lumen.
  5. Semen production: As sperm pass through the epididymis (maturation and storage) and vas deferens, the seminal vesicles (fructose-rich fluid), prostate (alkaline, enzyme-rich fluid), and bulbourethral glands (lubricating mucus) add secretions to form semen.
  6. Feedback: Testosterone inhibits GnRH and LH; inhibin from Sertoli cells inhibits FSH. These negative-feedback loops keep testosterone and sperm production within normal ranges.
  7. Erection (parasympathetic): Sexual stimulation activates parasympathetic nerves that release nitric oxide in penile arterioles. NO activates guanylate cyclase → cGMP, relaxing vascular smooth muscle, increasing blood flow into the erectile tissue and trapping it to produce erection.
  8. Ejaculation (sympathetic): Sympathetic nerves trigger contraction of the epididymis, vas deferens, seminal vesicles, and prostate to propel semen into the urethra (emission), followed by rhythmic contraction of pelvic muscles (ejaculation).

Key takeaways

  • High yield: Spermatogenesis happens in the seminiferous tubules; testosterone is made by the Leydig cells; Sertoli cells support the germ cells.
  • High yield: FSH → Sertoli cells (spermatogenesis support + inhibin); LH → Leydig cells (testosterone).
  • High yield: Testosterone inhibits GnRH/LH, while inhibin selectively inhibits FSH — a two-signal feedback system.
  • High yield: Erection is parasympathetic and nitric-oxide (cGMP) mediated; ejaculation is sympathetic.
  • Spermatogenesis includes meiosis, which halves the chromosome number to 23.
  • The blood-testis barrier, formed by Sertoli cells, protects developing sperm from immune attack and controls their environment.
  • Semen = sperm + secretions from seminal vesicles, prostate, and bulbourethral glands.
  • Testosterone is required both for spermatogenesis and for male secondary sex characteristics.

Keep learning

Ready to build on this? Continue to the next lesson.

Study tools & related lessonsYou’ll learn to · Key vocabulary · Related

You’ll learn to

  • Describe testicular anatomy, including the seminiferous tubules, Sertoli cells, and Leydig cells.
  • Trace the steps of spermatogenesis and the contributions to semen production.
  • Explain the hypothalamic-pituitary-gonadal (HPG) axis and the roles of GnRH, FSH, LH, testosterone, and inhibin, including feedback.
  • Distinguish the neural control of erection (parasympathetic/nitric oxide) from ejaculation (sympathetic).

Key vocabulary

Seminiferous tubules
Coiled tubules where sperm are made
Sertoli cells
Supporting cells lining the tubules
Leydig cells
Interstitial cells between the tubules
Spermatogenesis
Production of mature sperm from stem cells
GnRH
Hypothalamic hormone driving FSH and LH
FSH
Pituitary hormone acting on Sertoli cells
LH
Pituitary hormone acting on Leydig cells
Testosterone
Main male androgen
Inhibin
Sertoli-cell hormone
Nitric oxide (NO)
Vasodilator released during erection

Educational content only. It is not medical, legal or professional advice. Found an error? Tell us.