Semen

• Semen is a bodily fluid containing sperm and seminal plasma, vital for reproduction.
• It is composed of contributions from the testes, seminal vesicles, prostate gland, and bulbourethral glands.
• The primary function of Semen is to transport and protect sperm, facilitating fertilization.
• Semen production involves a coordinated process across several male reproductive organs.

What is Semen? Definition and Composition

Semen refers to the complex biological fluid expelled from the male reproductive tract during ejaculation. It is a heterogeneous mixture primarily composed of spermatozoa (sperm) and seminal plasma, which serves as a protective and nourishing medium for the sperm. The semen definition and meaning highlights its crucial role as the vehicle for male gametes, essential for sexual reproduction. Typically, Semen is a whitish or grayish fluid with a characteristic odor, and its consistency can vary.

What is semen made of involves a precise combination of contributions from several male accessory glands. While the testes are responsible for producing spermatozoa, the bulk of Semen’s volume, known as seminal plasma, originates from the seminal vesicles, prostate gland, and bulbourethral glands. Each component plays a vital role in ensuring sperm viability and function.

• Spermatozoa: These are the microscopic male reproductive cells, produced in the seminiferous tubules of the testes, carrying genetic material for fertilization.
• Seminal Vesicle Fluid: Constituting approximately 60-70% of the total semen volume, this alkaline, yellowish fluid is rich in fructose, a primary energy source for sperm motility, and prostaglandins, which may aid sperm transport.
• Prostatic Fluid: Making up about 20-30% of the semen volume, this milky, slightly acidic fluid contains citrate (a nutrient), seminalplasmin (an antibiotic), and prostate-specific antigen (PSA), an enzyme that helps liquefy coagulated Semen post-ejaculation, enhancing sperm mobility.
• Bulbourethral Gland Fluid: This clear, viscous fluid is secreted before ejaculation. Its primary function is to lubricate the urethra and neutralize any residual acidity from urine, creating a more favorable environment for sperm passage.

How is Semen Produced and Its Function?

The intricate process of how is semen produced begins in the testes with spermatogenesis, the continuous formation of spermatozoa within the seminiferous tubules. After development, these sperm travel to the epididymis, where they mature and gain motility. Mature sperm are then stored in the vas deferens, awaiting ejaculation.

During sexual arousal and ejaculation, sperm move from the vas deferens and mix sequentially with fluids from the accessory glands. The seminal vesicles contribute their fructose-rich fluid first, followed by the prostate gland’s milky, enzyme-containing secretions. Finally, the bulbourethral glands release their lubricating fluid into the urethra. This combined mixture forms Semen, which is then forcefully expelled. This process is tightly regulated by the nervous system and male hormones.

The multifaceted function of human semen is primarily to ensure the successful delivery and survival of sperm, thereby facilitating fertilization. Its roles include:

• Sperm Transport: Semen acts as the essential medium for transporting millions of sperm through the female reproductive tract towards the ovum.
• Protection and Buffering: The seminal plasma is alkaline, neutralizing the naturally acidic environment of the vagina, which is crucial for sperm survival.
• Nutrient Supply: Fructose provides the necessary energy for sperm to maintain vigorous motility, enabling them to swim effectively towards the egg.
• Enhancement of Motility: Components within seminal fluid can aid in sperm capacitation and hyperactivation, processes that enhance sperm’s ability to fertilize an egg.
• Immune Modulation: Semen contains factors that can temporarily suppress the female immune response in the reproductive tract, preventing the rejection of sperm.

According to the World Health Organization (WHO), a typical ejaculate volume in fertile men ranges from 1.5 to 7.6 milliliters, with a sperm concentration of at least 15 million sperm per milliliter considered a normal threshold for fertility assessment (WHO Laboratory Manual for the Examination and Processing of Human Semen, 5th edition). These parameters are vital indicators of reproductive health.