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Urinalysis & Body Fluids

Physiology

We are transitioning to a topic that is fundamentally different from the other body fluids we’ve discussed. While fluids like CSF, synovial, and serous fluids are ultrafiltrates of plasma that reflect a state of health or disease, semen is not a filtrate. It is a highly specialized, actively secreted, composite fluid

Its singular biological purpose is the successful fertilization of an ovum. Therefore, every single component we measure in a semen analysis is a direct reflection of the functional integrity of a specific part of the male reproductive tract. A semen analysis is, in essence, a functional bioassay of male reproductive health. To interpret the results, you must first become an expert in how this remarkable fluid is produced

Semen is not simply “sperm in fluid.” It is a sophisticated transport vehicle, complete with a fuel source, a protective suspension system, and enzymes designed to overcome the hostile environment of the female reproductive tract. It is produced by the coordinated effort of several different glands, each adding a unique and essential set of ingredients

Cellular Component: Spermatogenesis & Maturation

Before we discuss the fluid, we must understand the “cargo.”

  • Testes (The Production Factory)
    • Spermatozoa are produced within the seminiferous tubules: of the testes in a process called spermatogenesis. This is under the control of Follicle-Stimulating Hormone (FSH) from the pituitary and testosterone produced locally by Leydig cells in the testes
    • This process takes approximately 74 days. The sperm produced here are non-motile and incapable of fertilization.
  • Epididymis (The Finishing School & Storage Warehouse)
    • This is arguably the most critical and often overlooked organ. After leaving the testes, sperm spend about 12-14 days slowly traversing the long, coiled tube of the epididymis
    • This is where maturation occurs.: During this transit, sperm undergo critical biochemical changes to their cell membranes and acquire the potential for forward progressive motility.
    • The epididymis is also where sperm are concentrated (by reabsorbing fluid) and stored prior to ejaculation
    • Clinical Significance: Any pathology or blockage in the epididymis can prevent sperm maturation or release, leading to poor motility or azoospermia (absence of sperm), even if production in the testes is perfectly normal

Fluid Component: A Symphony of Glandular Secretions

The fluid portion of semen, known as the seminal plasma, is a mixture of secretions from three main accessory glands. They contribute in a specific order during ejaculation

1. Seminal Vesicles (The Main Fuel Tank & Gel Producer)

These two glands are the single largest contributor to the final semen volume

  • Contribution: Approximately 60-70% of the total ejaculate volume
  • Key Secretions & Their Functions
    1. Fructose: This is the hallmark biochemical marker of the seminal vesicles
      • Function: Fructose is a simple sugar that serves as the primary energy source for sperm motility. Sperm metabolize fructose to produce the ATP needed to power the flagellar whipping motion
      • Laboratory Significance: The presence of fructose in semen is proof that the seminal vesicles are functional and the ejaculatory ducts are patent (open). A low volume ejaculate with an absence of fructose is a critical finding that points directly to a congenital absence of the seminal vesicles or an obstruction of the ejaculatory duct
    2. Fibrinogen-like Substance: This is a clotting protein
      • Function: Upon ejaculation, this protein is acted upon by enzymes from the prostate, causing the initial coagulation of the semen into a gel-like consistency. This coagulum is thought to help hold the semen in the upper vagina near the cervix, preventing immediate loss
    3. Prostaglandins
      • Function: These signaling molecules are thought to aid in fertilization by stimulating contractions in the female reproductive tract (uterus and fallopian tubes), helping to propel the sperm toward the ovum. They also may help penetrate the cervical mucus
  • Fluid Properties: The fluid from the seminal vesicles is viscous and slightly alkaline

2. Prostate Gland (The Liquefaction Engine & pH Regulator)

The prostate is the second-largest contributor and provides the critical enzymes that “activate” the semen after ejaculation

  • Contribution: Approximately 20-30% of the total ejaculate volume
  • Key Secretions & Their Functions
    1. ENZYMES (Proteolytic Enzymes)
      • Prostate-Specific Antigen (PSA): While we know it as a blood test for prostate cancer, its primary physiological role is as a powerful enzyme in semen. PSA is a serine protease responsible for liquefaction. It breaks down the fibrinogen-like proteins from the seminal vesicles, causing the coagulum to liquefy over 15-60 minutes
      • Function: This liquefaction is absolutely critical. It frees the sperm from the gel matrix, allowing them to become motile and begin their journey through the cervix
      • Laboratory Significance: A specimen that fails to liquefy within 60 minutes points directly to a dysfunction of the prostate gland, specifically a deficiency in its enzymatic secretions
    2. CITRIC ACID & ZINC
      • Function: Citric acid helps maintain the proper osmotic balance of the semen. Zinc is crucial for stabilizing the DNA-containing chromatin in the sperm head and has antibacterial properties
    3. SPERMINE & SPERMIDINE
      • Function: These polyamines are responsible for the characteristic odor of semen
  • Fluid Properties: The prostatic fluid is a milky, watery fluid that is acidic (pH ~6.5). This acidic nature is important because it is balanced by the alkaline fluid from the seminal vesicles

3. Bulbourethral (Cowper’s) & Littre Glands

These are small glands that contribute a small but important pre-ejaculate fluid

  • Contribution: Approximately 5% of the total ejaculate volume
  • Key Secretion & Its Function
    • Thick, clear, alkaline mucus
      • Function 1 (Neutralization): This fluid is secreted during sexual arousal before ejaculation. Its primary role is to flow through the urethra to neutralize any residual acidic urine, which is spermicidal
      • Function 2 (Lubrication): It also serves to lubricate the urethra for the passage of the ejaculate

Final Product: Semen Physiology in Action

When we analyze a semen sample, we are witnessing the end result of this physiological symphony

  • Volume (Normal: 1.5 - 5.0 mL): A composite of all glands. Low volume points to incomplete collection, duct obstruction, or seminal vesicle aplasia
  • Coagulation & Liquefaction (Normal: Complete within 60 mins): A two-step process. First, seminal vesicle proteins cause coagulation. Second, prostate enzymes (PSA) cause liquefaction. A failure to liquefy is a prostatic problem
  • pH (Normal: 7.2 - 8.0): A delicate balance. The acidic prostatic fluid is buffered by the alkaline seminal vesicle and bulbourethral fluids.
    • An abnormally acidic pH (<7.2) with low volume and no fructose strongly suggests a problem with the alkaline seminal vesicles
  • Motility: A reflection of successful maturation in the epididymis and the availability of fructose from the seminal vesicles

Conclusion

Every parameter in a semen analysis is a question we are asking the male reproductive system. “Did the seminal vesicles provide fuel?” (Check fructose). “Did the prostate provide the liquefaction enzymes?” (Check liquefaction time). “Did the epididymis mature the sperm correctly?” (Check motility). By understanding the specific physiological contribution of each gland, you move from simply reporting numbers to being a true diagnostic consultant in the field of andrology