Part 11: Formation, Composition, and Examination Methods of Semen and Prostatic Fluid

◇A Guide to Caring for Your Husband's Health as a Good Wife◇

Previous articleBAO JIAN ZHI SHI

Health knowledge

How is semen produced?

Semen is composed of sperm produced by the male testes, secretions, and secretions from the reproductive tract glands (epididymis, prostate, seminal vesicles, urethral accessory glands, etc.). During ejaculation, the male reproductive glands do not empty simultaneously; the general order of emptying is: urethral glands, prostate, tail of the epididymis (sperm), and finally the seminal vesicles. Semen is generally grayish-white, has a certain viscosity and a distinctive odor; it is alkaline. In humans, each milliliter of semen contains 60 million to 150 million sperm. A typical ejaculation volume is 3-5 milliliters, therefore, each ejaculation releases approximately 120 million sperm.

Composition of semen

A normal male ejaculates 3-5 ml of semen during intercourse or masturbation. Semen is grayish-white, weakly alkaline, and has a distinctive fishy odor, primarily from the prostatic fluid. Seminal plasma comprises over 95% of the semen, while sperm makes up less than 1%. Each cubic centimeter of testicular tissue can produce 2 million sperm per day, meaning each male's testicles can produce tens to hundreds of millions of sperm daily. Even if not ejaculated, these sperm will age, die, and eventually be digested by enzymes.

Seminal plasma is a mixture of secretions from the Sertoli cells of the seminiferous tubules and the epididymis, prostate gland, seminal vesicles, bulbourethral glands, and paraurethral glands. The secretions from the seminal vesicles and prostate gland account for approximately 65% ​​and 30% of the total volume, respectively. Seminal plasma primarily provides a matrix for transporting and nourishing sperm, and also stimulates sperm motility.

Semen consists of sperm and seminal plasma. The main component of seminal plasma is water, accounting for more than 90%. Other components include fats, protein particles, pigment particles, phospholipid bodies, amines (choline, spermine, and spermine), free amino acids, inorganic salts, enzymes, and carbohydrates. These components are very similar to those of blood plasma, differing only in their origin, form, and function.

What is normal semen?

According to the World Health Organization's standards for normal semen, the following aspects can be analyzed to determine whether semen is normal:

◎Semen volume: Normal ≥2 ml. More than 7 ml is considered excessive, which not only reduces sperm density but also makes it easier for semen to flow out of the vagina, leading to a lower total sperm count. This is commonly seen in seminal vesiculitis. Less than 2 ml is considered insufficient, but usually less than 1 ml is considered too low. In this case, the contact area between the semen and the female reproductive tract is small, or the viscosity may hinder sperm from entering the cervix, leading to infertility. This is commonly seen in severe accessory gland inflammation, low testosterone levels, ejaculatory duct obstruction, retrograde ejaculation, etc.

◎Color: Normal semen is grayish-white or slightly yellow. Milky white or yellowish-green semen suggests inflammation of the reproductive tract or accessory glands; pink, red, or semen with red blood cells visible under a microscope indicates hemospermia, commonly seen in inflammation of the accessory glands or posterior urethra, and occasionally in tuberculosis or tumors.

◎pH: The normal pH value of semen is 7.2~7.8. A pH less than 7.2 is seen in ejaculatory duct obstruction or urine contamination, while a pH greater than 7.8 is often seen in seminal vesicle inflammation or old specimens.

◎Liquefaction Time: Normally, after ejaculation, semen becomes gel-like under the action of coagulating enzymes in the seminal vesicle. It then liquefies within 15-30 minutes under the action of liquefying enzymes in the prostate gland; this is called semen liquefaction. If semen fails to liquefy within 30 minutes of ejaculation, it is considered abnormal.

◎Viscosity: When a glass rod is brought into contact with liquefied semen and the rod is gently lifted, a semen thread will form. Normally, its length is less than 2 cm.

◎Sperm Count: Generally expressed as the number of sperm per milliliter of semen. A normal count is greater than 20 × 10⁶/ml. A count below this is considered oligospermia, seen in various causes of spermatogenesis disorders, which can lead to decreased fertility or infertility due to reduced chances of sperm entering the uterine cavity and fallopian tubes. A sperm count greater than 250 × 10⁶/ml is considered polyspermia, which can also lead to infertility due to impaired sperm motility.

◎Sperm morphology: More than 50% of sperm should have normal morphology; otherwise, it may cause infertility.

◎Motility: More than 50% of sperm exhibit rapid, linear forward movement.

◎Survival rate: Usually refers to the percentage of live sperm greater than 50% when examined within 1 hour after ejaculation. Common causes of decreased sperm motility and survival rate include accessory gland inflammation, varicocele, ciliary dysregulation syndrome caused by chronic respiratory tract infection, presence of antisperm antibodies in semen, or improper sample storage.

◎White blood cells: Normal semen contains less than 1×10⁶ white blood cells per milliliter. An increased white blood cell count indicates an infection in the reproductive tract or accessory glands.

How to collect and examine semen

During semen collection, changes in external temperature, oxygen pressure, pH, and chemical substances can all alter sperm composition. Therefore, the following precautions should be taken when collecting semen:

Avoid ejaculation for 3-5 days.

◎Semen should generally be collected by masturbation in a laboratory setting and stored in a clean, dry glass bottle.

◎If at home, collect the semen in a glass bottle using the external ejaculation method, and place it in an underwear bag close to your body. Send it for testing within 1 hour.

◎All semen ejaculated at one time must be collected in a glass bottle.

◎It is generally not advisable to use a penile sheath to collect semen, as the chemical action of the powder and latex film inside the sheath can affect sperm motility, and the semen tends to adhere inside the sheath, making it impossible to send the entire semen sample for testing. Semen analysis includes data such as volume, color, viscosity, pH, sperm count, sperm motility, and sperm morphology.

Properties of prostatic fluid

In appearance, normal prostatic fluid is thin, pale milky white, with a protein-like sheen and a distinctive odor. In severe inflammation, the prostatic fluid becomes thick, yellowish or pale red, cloudy, and contains flocculent material and filaments. Under low magnification, normal samples show lecithin bodies of varying sizes, slightly smaller than red blood cells, which, due to their refractive properties, appear as bright little beads. In samples from inflamed patients, these lecithin bodies are significantly reduced and tend to clump together. Under high magnification, normal samples contain no more than 10 white blood cells, while in inflamed samples, the number of white blood cells is significantly increased and often present in clumps. Inflammation of the seminal vesicles or excessive force during massage sampling can cause red blood cells to appear in the prostatic fluid. Clinically, the prostatic fluid examined is collected through massage; strictly speaking, it is secretion from the prostate gland in a resting state, mixed with a small amount of seminal vesicle fluid. It does not represent the prostatic secretions released into the semen during ejaculation.

In addition to the above-mentioned examinations, a thin, uniform smear of the specimen, after drying, can be fixed and stained to check the number and type of bacteria. However, if genital tuberculosis is confirmed or highly suspected, prostate massage is generally not performed to avoid causing the spread of tuberculosis.

In hospitals, prostate fluid is typically collected using the four-glass method. First, 10 ml of urine is collected, representing the urethral specimen. Then, 200 ml of urine is urinated and discarded. Another 10 ml of urine is collected, representing the midstream urine. Prostate fluid is then collected through massage. After the massage, urine is urinated again, and the first 10 ml is collected, representing the prostate and posterior urethra. The four specimens are then subjected to microscopic examination, cell counting, culture, and antibiotic sensitivity testing. This method aids in localization and diagnosis.

Relationship between biochemical indicators of prostatic fluid and diseases

The pH value, acid phosphatase concentration, zinc ion concentration, leucine aminopeptidase activity, and citric acid concentration of prostatic fluid are easily affected by pathological conditions such as infection, and can all be used to diagnose diseases.

◎pH: Under normal circumstances, the pH range is approximately 6.7 to 7.3. The pH of prostatic fluid becomes more alkaline with age. When inflammation occurs, the pH can increase to 7.7 to 8.5.

◎Zinc Ion Concentration: The prostate gland has the highest zinc content of any tissue in the body, and the zinc concentration in prostatic fluid is also very high. The prostate gland can synthesize zinc-containing polypeptides with antibacterial effects; therefore, the zinc content is related to the bactericidal ability and antibacterial defense mechanism of prostatic fluid. In chronic prostatitis, the zinc concentration drops from approximately 480 micrograms/ml to approximately 148 micrograms/ml. When ejaculatory duct obstruction leads to azoospermia, the zinc concentration in semen increases significantly, due to a significant increase in the proportion of prostatic fluid in the semen.

◎Citrate Concentration: Citrate mainly originates from the prostate gland, and its secretion is controlled and regulated by androgens. Citrate levels are positively correlated with zinc concentration (i.e., when one increases, the other also increases proportionally). Normal citrate concentration is approximately 19 mg/mL, while in patients it is approximately 6.4 mg/mL.

◎Acid phosphatase content: Acid phosphatase mainly originates from the prostate gland. Its content is positively correlated with zinc concentration. Both are significantly elevated in prostate cancer. Therefore, acid phosphatase content can serve as an objective indicator for diagnosis, treatment, and follow-up. Its content decreases significantly after castration.

◎Immunoglobulin content: Type A immunoglobulin has diagnostic value; its normal concentration is 1500 times higher than that in the blood.