The seminal vesicles are integral glands in the male reproductive system, contributing significantly to semen composition. They contribute a large portion of the fluid that carries sperm, creating an environment conducive to successful reproduction. Understanding their function offers insight into the complex processes of male fertility.
Where Are Seminal Vesicles Located?
The seminal vesicles are a pair of glandular structures situated within the male pelvis. They are located behind the bladder and above the prostate gland. This placement puts them in front of the rectum, separated by a layer of tissue known as the rectoprostatic fascia.
Each seminal vesicle is a coiled or twisted tubular gland, typically measuring about 5 cm in length, extending to 10-15 cm when uncoiled. The excretory duct of each seminal vesicle joins the vas deferens, which transports sperm, to form the ejaculatory duct. These ejaculatory ducts then pass through the prostate gland before opening into the prostatic urethra.
What Do Seminal Vesicles Produce?
The seminal vesicles produce a fluid that constitutes a significant portion of semen, typically contributing about 50-80% of its total volume. This fluid is yellowish, thick, and viscous. It is also alkaline, helping to neutralize acidic environments.
The seminal fluid contains several biochemical substances. These include fructose (a sugar), along with proteins, citric acid, and inorganic phosphorus. Prostaglandins and ascorbic acid (Vitamin C) are also present. These components contribute to the environment necessary for sperm survival and function.
Why Is Seminal Fluid Important?
Seminal fluid provides the necessary support for sperm as they navigate the female reproductive tract. Fructose, a sugar found in the seminal fluid, serves as the primary energy source for sperm. This energy enables sperm motility, allowing them to swim toward the egg.
Prostaglandins play a role in stimulating smooth muscle contractions in the female reproductive tract. These contractions, particularly in the uterus and fallopian tubes, propel sperm towards the egg, aiding sperm transport. Some research suggests prostaglandins may also directly influence sperm motility.
Clotting proteins, such as seminogelin, are also secreted by the seminal vesicles. These proteins cause semen to coagulate shortly after ejaculation, forming a gel-like matrix that prevents it from flowing out of the vagina. This coagulation allows time for the sperm to begin their journey before prostate-specific antigen (PSA), an enzyme from the prostate gland, later liquefies the coagulum, enabling sperm to move more freely.
The alkaline nature of seminal fluid is also beneficial, as it helps to neutralize the naturally acidic environment of the vagina. This neutralization protects sperm from acidic conditions, which can impair their viability and motility, enhancing their chances of survival. Additionally, ascorbic acid (Vitamin C) acts as an antioxidant within the seminal fluid, helping to protect sperm from oxidative damage.