Sperm maturation, semen and semen analysis
- Measurement
- Exam priority: medium
Sperm made in the testis learn to swim in the epididymis; glands add fluid that feeds and protects them. A semen test checks both.
Also called: Spermogram, Seminal fluid
See it in 3D: Testes · Epididymis · Prostate
What it is
Sperm leave the seminiferous tubules unable to swim or fertilize. They gain these abilities during about two weeks of transit through the epididymis and are stored mainly in its tail and in the vas deferens. At ejaculation they are mixed with secretions from the seminal vesicles, prostate and bulbourethral glands, which make up most of the semen volume. Semen analysis measures the result of both processes: how many sperm, how well they move, their shape, and the chemistry of the fluid.
Key facts
- Spermatogenesis takes ≈ 64–74 days, plus ≈ 10–14 days of epididymal transit: a cause that harms sperm (fever, drug, heat) shows up in semen about 2–3 months later.
- Scrotal temperature is ≈ 2–3 °C below core temperature; varicocele, fever and heat exposure lower sperm output.
- Mature sperm: head (nucleus + acrosome), midpiece (mitochondria that make ATP from fructose), tail (flagellum).
- Stored sperm stay fertile for weeks in the male ducts; after ejaculation they survive in cervical mucus for up to about 5 days.
- Sperm are only ≈ 1–5% of semen volume; vasectomy barely changes the volume a man sees.
How it works, step by step
- Spermatids are released into the tubule lumen as spermatozoa and carried passively by fluid and peristalsis to the epididymis.
- In the head and body of the epididymis, the sperm membrane is remodelled and proteins are added: sperm gain forward motility.
- The epididymal fluid is slightly acidic and holds inhibitory factors, so stored sperm stay quiet and use little energy.
- At emission (sympathetic, T11–L2), smooth muscle of the epididymis, vas deferens, seminal vesicles and prostate empties into the posterior urethra.
- Seminal vesicle proteins (semenogelins) form a coagulum that holds sperm near the cervix; PSA then cuts them and the semen liquefies.
- Alkaline seminal fluid buffers the acidic vagina, which would otherwise stop sperm motility.
- In the female tract, capacitation removes cholesterol and coating proteins, raises intracellular Ca²⁺ and starts hyperactivated motility.
- At the zona pellucida, the acrosome reaction releases enzymes that let one sperm reach and fuse with the oocyte.
Semen analysis: usual reference values (MedlinePlus, based on WHO criteria)
| Parameter | Value | Note |
|---|---|---|
| Volume | 1.5–7.6 mL | after 2–5 days of abstinence |
| Sperm concentration | 15–259 million/mL | |
| Total sperm count | > 39 million per ejaculate | |
| Motility | > 40% | moving sperm |
| Normal morphology | > 4% | strict criteria |
| pH | 7.2–8.0 | |
| Liquefaction | 15–30 min | |
| White blood cells | < 1 million/mL | more suggests infection or inflammation |
Approximate values for a healthy adult at rest; each laboratory sets its own ranges.
Where each part of semen comes from
| Source | Share of volume | Key contents | If missing |
|---|---|---|---|
| Testis and epididymis | ≈ 5–10% | Sperm, epididymal proteins | Azoospermia, normal volume and fructose |
| Seminal vesicles | ≈ 60–70% | Fructose, prostaglandins, semenogelins (clotting), alkaline fluid | Low volume, no fructose, acidic pH, no coagulum |
| Prostate | ≈ 20–30% | Citrate, zinc, acid phosphatase, PSA (liquefaction) | Semen fails to liquefy |
| Bulbourethral glands | small | Mucus that lubricates the urethra (pre-ejaculate) | Little effect on analysis |
Clinical notes
- Male factor contributes to about half of couples' infertility, which is why semen analysis is an early, cheap test.
- Oligospermia with high FSH points to primary testicular failure; with low FSH and LH to hypogonadotropic hypogonadism.
- Exogenous testosterone or anabolic steroids suppress LH and FSH and can cause azoospermia despite high androgen levels.
- Antisperm antibodies or many white cells cause sperm clumping (agglutination) and poor motility.
Test yourself
Think of the answer, then tap the question to see it.
A man has semen volume 0.6 mL, pH 6.8, no sperm and no fructose. Which structures are most likely absent or blocked?
The seminal vesicles' contribution is missing: ejaculatory duct obstruction or congenital absence of the vas deferens and seminal vesicles, often with CFTR mutations.
Where do sperm first gain the ability to swim forward?
In the epididymis, during roughly two weeks of transit; sperm leaving the testis are immotile. Full fertilizing ability comes with capacitation in the female tract.
Why does a high fever affect a semen analysis about 2–3 months later rather than the next week?
Spermatogenesis takes about 64–74 days plus epididymal transit, so cells damaged during development reach the ejaculate weeks to months later.
Which prostatic enzyme liquefies the semen clot, and which gland makes the clot?
PSA, a serine protease from the prostate, cleaves semenogelins, the clotting proteins made by the seminal vesicles.
Connections
See it in 3D3
The structures of Durgical's 3D anatomy where it happens.
In Biochemistry1
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: Semen Analysis: MedlinePlus Medical Test (MedlinePlus, US National Library of Medicine, 2026); Varicocele (StatPearls (NCBI Bookshelf), 2023).
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Representative model, for educational purposes only.