Semen refers to the fluid expelled from the urethra during male ejaculation (typically occurring during sexual climax). Normal semen is a viscous mixture composed of sperm and seminal plasma. Sperm are produced in the testes, mature in the epididymis, and are transported through the vas deferens.Seminal plasma primarily consists of a mixture secreted by accessory glands such as the prostate, seminal vesicles, and bulbourethral glands, along with small amounts of testicular fluid and epididymal fluid. Under normal conditions, sperm and seminal plasma components remain separate. During ejaculation, they mix to form semen.
Semen quality directly impacts the health of future children. Men naturally desire healthy offspring, making rigorous semen quality assessment essential. Close observation reveals variations: some men exhibit yellow semen, others milky white, and rarely, greenish semen. A healthy semen standard exists for reference.
1. Volume: Normal ≥2ml. Volumes exceeding 7ml are excessive, reducing sperm density and increasing leakage from the vagina, which lowers total sperm count—commonly seen in seminal vesiculitis. Volumes below 2ml indicate low semen volume, with less than 1ml typically considered insufficient.In such cases, the contact area between semen and the female reproductive tract is reduced, or viscosity hinders sperm entry into the cervical opening, potentially causing infertility. This is commonly seen in severe inflammation of the accessory glands, low testosterone levels, ejaculatory duct obstruction, or retrograde ejaculation.
2. Color: Normal semen appears grayish-white or slightly yellow. A milky white or yellowish-green hue suggests inflammation in the reproductive tract or accessory glands. Pink, red, or the presence of red blood cells under microscopy indicates bloody semen, commonly seen in inflammation of the accessory glands or posterior urethra, and occasionally in tuberculosis or tumors.
3. Acidity/Alkalinity: Normal semen pH ranges from 7.2 to 7.8.Values below 7.2 indicate ejaculatory duct obstruction or urine contamination; values above 7.8 suggest seminal vesicle inflammation or an aged sample.
4. Liquefaction time: After ejaculation, semen initially solidifies into a gel-like state due to seminal vesicle coagulase. Within 15–30 minutes, prostate liquefying enzymes convert it into a liquid state—this process is semen liquefaction.Failure to liquefy within 30 minutes post-ejaculation indicates abnormality.
5. Viscosity: Gently lifting a glass rod dipped into liquefied semen should form a semen thread. Normal length is <2 cm.
6. Sperm Count: Typically expressed as sperm per milliliter of semen. Normal count ≥20×10⁶/ml.Values below this indicate oligospermia (low sperm count), often due to spermatogenic dysfunction from various causes. This reduces sperm access to the uterine cavity and fallopian tubes, leading to subfertility or infertility. A count exceeding 250×10⁶/ml indicates polyzoospermia (high sperm count), which may impair motility and also cause infertility.
7. Sperm morphology: ≥50% of sperm should exhibit normal morphology; otherwise, infertility may result.
8. Motility: ≥50% of sperm should demonstrate rapid, straight-line forward movement.
9. Survival Rate: Typically assessed within one hour post-ejaculation, with ≥50% live sperm. Common causes of reduced motility and survival include inflammation of accessory glands, varicocele, ciliary dyskinesia syndrome from chronic respiratory infections, presence of anti-sperm antibodies in semen, or improper specimen storage.
10. Leukocytes: Normal semen contains <1×10⁶/ml leukocytes. Elevated leukocyte counts indicate infection in the reproductive tract or accessory glands.
Compared to other bodily fluids like saliva, gastrointestinal fluids, or blood, semen possesses the most distinct odor.Semen is a mixture. Besides sperm, seminal plasma consists of prostate fluid, epididymal fluid, seminal vesicle fluid, and various secretions from the urethra and vas deferens.
The characteristic odor of normal semen originates from the oxidation of a chemical called spermidine, resembling the scent of chestnut blossoms. Spermidine is one of several key components in prostate secretions.The oxidation of spermidine requires the participation of seminal vesicle fluid. Prostatic fluid obtained through rectal massage typically lacks the characteristic odor present in naturally ejaculated semen.
Thus, the odor of normal ejaculate originates from the prostate but is only released with the involvement of seminal vesicle fluid. The absence of this distinctive odor often indicates impaired prostate function, and many prostate patients exhibit semen devoid of this scent.