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 dayst_{ ext{maturation}} \,=\, 74 \text{ 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%25\% of seminal fluid.

Prostate and seminal vesicles: contributions and components

  • Prostate gland adds fluid downstream of the ejaculatory ducts and contributes approximately 25%25\% of the seminal fluid.
  • Prostatic fluid components include: citric acid, acid phosphatase, proteolytic enzymes, proteins, and zinc.\text{citric acid}, \ \text{acid phosphatase}, \ \text{proteolytic enzymes}, \ \text{proteins}, \ \text{and } \text{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 hours48\ \text{hours} and no longer than 7 days7\ \text{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 minutes30\ \text{minutes} to 1 hour1\ hour; maintain temperature between 2040C20-40^{\circ}\text{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 hour1\ hour and kept between 2040C20-40^{\circ}\text{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 weeks12\ 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\le 30\ \text{minutes}; if liquefaction is delayed beyond 60 minutes it may still be considered abnormal.
    • Odor: musty and distinctive.
    • Typical volume: 25 mL2-5\ \text{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 cm2\ \text{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 units200\ \text{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/mLC = N \times 10^6 \ \text{ sperm/mL}; normal is 200 to 250×106  sperm/mL200 \text{ to } 250 \times 10^6 \ \text{ 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/mL1\times 10^6/\text{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%\ge 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 weeks12\ \text{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.