The seminal vesicles are a pair of glandular organs integral to the male reproductive system. They are responsible for producing a large portion of the fluid that eventually becomes semen. This nutrient-rich liquid supports the survival and movement of sperm cells after ejaculation.
Where the Seminal Vesicles Are Located
The two seminal vesicles are situated deep within the male pelvis, positioned behind the urinary bladder and directly above the prostate gland. They are separated from the rectum by a layer of tissue known as Denonvillier’s fascia. Each vesicle is an elongated, coiled, sac-like structure, measuring about five centimeters in length.
At the lower, narrow end of each seminal vesicle, a small duct forms and merges with the corresponding vas deferens, the tube that carries sperm. This union creates the ejaculatory duct, which then passes through the prostate gland before emptying into the urethra. The location ensures that the fluid from the seminal vesicles mixes with the sperm and prostatic secretions just before ejaculation occurs.
The Essential Role in Semen Composition
The primary function of the seminal vesicles is the rapid production and secretion of seminal fluid. This fluid constitutes approximately 60 to 80 percent of the total volume of the ejaculate. The composition is highly specialized, designed to protect and nourish the sperm cells during their journey.
One important component is fructose, a simple sugar that serves as the main energy source for sperm motility. Without this fuel, sperm quickly lose their ability to swim and reach the egg. The fluid also contains prostaglandins, hormone-like compounds thought to help suppress the female immune response to sperm. Prostaglandins may also induce smooth muscle contractions in the female reproductive tract, facilitating sperm transport toward the uterus and fallopian tubes.
Another component is an alkaline fluid, which helps neutralize the naturally acidic environment of the male urethra and female vagina. This alkalinity creates a more favorable environment for sperm survival. The secretion also contains clotting factors, which cause the semen to temporarily thicken after ejaculation. This temporary coagulation is thought to help hold the semen within the female reproductive tract, increasing the probability of fertilization.
Clinical Conditions Affecting the Seminal Vesicles
The seminal vesicles can be affected by various medical conditions, often due to their close proximity to the prostate and urinary tract. One common issue is inflammation, known as seminal vesiculitis, which typically occurs secondary to an infection in the prostate or epididymis. This inflammation can lead to symptoms like hematospermia (blood in the semen) and painful ejaculation.
Blockages in the ejaculatory ducts are another concern, which can be caused by acquired cysts, congenital abnormalities, or small stones (calculi). An obstruction can prevent the seminal fluid from exiting the gland, potentially leading to discomfort, reduced ejaculate volume, and male infertility. A rare congenital condition called Zinner syndrome involves a triad of an ipsilateral seminal vesicle cyst, ejaculatory duct obstruction, and kidney agenesis.
While primary cancer of the seminal vesicle is exceedingly rare, the glands are often involved in the spread of more common cancers, particularly advanced prostate cancer. Diagnosis of seminal vesicle pathology frequently relies on imaging techniques, such as trans-rectal ultrasound (TRUS) or magnetic resonance imaging (MRI). The level of fructose in a semen sample can also be analyzed to indirectly assess the functional status or patency of the seminal vesicles.