Semen Fluid, Anatomy, Collection, and Analysis: Comprehensive Notes
Seminal Fluid: origin and key components
- Seminal fluid is made up of secretions from the testes, the epididymis, seminal vesicles, the prostate gland, and the bulbar urethral glands (a very small amount).
- Testes produce testosterone and sperm; production is regulated by FSH and LH from the anterior pituitary.
- The seminal vesicles and the prostate are the major contributors of the seminal fluid.
- Spermatozoa are produced in the testes, mature and concentrate in the epididymis, and then comprise a small fraction of the fluid.
- Time to maturation of sperm is about textmaturation=74 days.
Anatomy and pathway of semen production
- Anatomy shown: testes, surrounded by the epididymis, then vas deferens, ampulla, seminal vesicle, ejaculatory duct, urethra; prostate contributes fluid as semen travels through it.
- Seminiferous tubules are inside the testes; the interstitium is outside the cells.
- Two testes located outside the abdominal cavity; required for spermatogenesis (formation of sperm).
- Germ cells line the seminiferous tubules: spermatogonia undergo mitosis and meiosis to produce germ cells and spermatids; at this point the sperm are non-motile.
- Sertoli cells line the seminiferous tubules; they provide nutrients and hormones for spermatogenesis and help regulate movement of sperm into the semen.
- Epididymis (outside the testes) is where final maturation and motility of sperm occur; semen is highly concentrated here and stored until ejaculation.
- After ejaculation, sperm enter the vas deferens, which leads to the urethra via the ejaculatory duct; the vas deferens can be interrupted by a vasectomy (clipping the vas deferens).
- The fluid then passes through the prostate; the prostate contributes fluid and makes up about 25% of seminal fluid.
Prostate and seminal vesicles: contributions and components
- Prostate gland adds fluid downstream of the ejaculatory ducts and contributes approximately 25% of the seminal fluid.
- Prostatic fluid components include: citric acid, acid phosphatase, proteolytic enzymes, proteins, and zinc.
- Acid phosphatase is present in sperm but not in female vaginal secretions; its presence can aid in forensic analysis (rape or sexual assault cases).
- Zinc levels can be used to evaluate prostate function.
- Seminal vesicles add fluid rich in flavin, fructose, proteins, and prostaglandins:
- Flavin imparts the gray-white color and causes fluorescence under UV light.
- Fructose provides a necessary nutrient for sperm.
- Proteins help the semen coagulate after ejaculation.
- Prostatic fluid markers and cooperation with chemical tests help assess fertility and prostate function.
Semen specimen collection: instructions and handling
- Specimen collection is patient-collected (self-collection) with proper instruction from healthcare providers.
- Abstinence period required: between 48 hours and no longer than 7 days prior to collection.
- Collection method: masturbation into a sterile container (glass or plastic); no lubricants or condoms.
- Specimen should be delivered to the lab as soon as possible, ideally within 30 minutes to 1 hour; maintain temperature between 20−40∘C (body temperature).
- The entire ejaculate must be collected.
- Labeling: full name, date and time of collection, and period of abstinence.
- In-house collection is preferred but it can be brought in; postcoital samples may be collected in the physician’s office.
- All specimens should be analyzed within 1 hour and kept between 20−40∘C; improper handling can affect motility and liquefaction times.
- Postvasectomy follow-up requires two collections; any presence of sperm is significant (even a single sperm means ongoing fertility; aim is zero sperm after ~12 weeks post-procedure).
- Sperm washes can be performed to concentrate sperm for intrauterine insemination (IUI) when needed.
Semen analysis: overall workflow and what is assessed
- Physical (macroscopic) examination:
- Appearance: typically gray to opaque and fairly turbid.
- Abnormal colors: brown or yellow; abnormal turbidity.
- Semen should coagulate immediately after collection and liquefy within ≤30 minutes; if liquefaction is delayed beyond 60 minutes it may still be considered abnormal.
- Odor: musty and distinctive.
- Typical volume: 2−5 mL.
- Turbidity: very high turbidity may indicate issues; decreased turbidity can suggest low sperm count.
- Viscosity: reviewed after liquefaction; use a pipette to observe droplets; normal semen is watery with discrete droplets; being stringy (>2 cm) is abnormal.
- Chemical (biochemical) examination:
- pH: normal semen is slightly alkaline; values:
- \text{pH} > 7.8 \Rightarrow \text{infection or abnormality}
- \text{pH} < 7.2 \Rightarrow \text{epididymal, fast efferents, or seminal vesicle abnormalities}
- Acid phosphatase: normally > 200 units; not present in vaginal secretions; usage in forensic contexts (rape or sexual assault) to indicate semen presence.
- Fructose: a key energy source for sperm; can be measured even if no sperm present; decreased fructose can contribute to infertility.
- Zinc and citric acid: used to evaluate prostate and seminal vesicle function respectively.
- Hormones: measured in some contexts for infertility or diseased hormone states (details to be covered in later hormone units).
- Microscopic examination:
- Motility (most important fertility parameter): assessed by phase-contrast microscopy; evaluate 6–10 high-power fields or ~100 sperm at 400x; grade on a 0–4+ scale; aim for 4+ forward progression; normal is >50% with linear forward progression.
- Concentration: typically perform a 1:20 dilution; count five squares in the center square and the four corner squares; total counted N; concentration is C=N×106 sperm/mL; normal is 200 to 250×106 sperm/mL.
- MacConkey or other chamber adjustments: if using a macular chamber, a dilution is not required; concentration values are already adjusted.
- Morphology: subjective assessment of 100–200 sperm observed at 1000x (oil immersion); smear fresh semen, stain (e.g., hematology-type stain); >50% normal forms is considered normal; evaluate head, midpiece, and tail morphology.
- White blood cell (WBC) count: should be < 1×106/mL (normal reference).
- Viability: use a viability stain; dead sperm take up the stain (often appear red); live sperm do not; normal fertility requires at least ≥50% viable sperm.
- Agglutination: graded as few, moderate, or many; clumping of sperm; presence may indicate antisperm antibodies (could be from the female or male); even small amounts in live sperm are abnormal.
- Final notes for semen analysis:
- Post-vasectomy assessments require evaluating two collections; any detectable sperm is clinically significant; the goal is zero sperm after an adequate waiting period (generally ~12 weeks).
- Sperm washing can be used to concentrate sperm for IUI when needed.
- Postcoital samples: collected after intercourse for assessment of agglutination and motility in couples with fertility issues or suspected antisperm antibodies.
Key takeaways and clinical implications
- The male reproductive tract and seminal fluids are a coordinated system where the testes produce sperm and regulate testosterone; accessory glands (seminal vesicles and prostate) contribute fluids that provide energy, protection, and coagulation properties to semen.
- Proper collection, handling, and timing are critical for accurate semen analysis; delays or temperature deviations can alter motility and liquefaction times.
- Semen analysis combines physical, chemical, and microscopic assessments to evaluate fertility potential and diagnose infertility causes, post-vasectomy sterility, or forensic evidence.
- For fertility assessment, multiple semen samples over a ~3-month period improve diagnostic accuracy due to the 74-day sperm maturation cycle and natural variability.