Seminal vesicles (also known as the vesicular or seminal glands) are a pair of glands located in the male’s pelvis, between the bladder and rectum. These vesicles are responsible for producing around 60% of the fluid that eventually becomes semen. The remaining fluid is created by the prostate and bulbourethral glands.

What are the seminal vesicles?

The seminal vesicles are two glands located behind the bladder and above the prostate gland. They produce and secrete between 50–65% of the fluids that make up semen, including the fructose that provides nutrients for sperm. The fluid also serves to increase the pH of the semen before it encounters acidity within the vagina.

Around 2–4 cm long, each of the seminal vesicles is made up of a coiled tube, measuring around 10 cm long when straightened. The tube has three layers: 

• inner mucosal layer
• muscular layer
• outer fibrous tissue layer

The seminal vesicles come together with the vas deferens to form the ejaculatory duct. During ejaculation, the seminal vesicles and the prostate gland contract to send fluid into the urethra.

Seminal vesicles and male fertility

If you produce lower than normal amounts of semen or if the semen lacks fructose, there may be a problem with the seminal vesicles. The pH of semen can also help reveal the health of the seminal vesicles, with acidic semen (pH less than 7.2) suggesting blocked seminal vesicles and alkaline semen above pH 8.0 indicating that there may be an infection.

Each of these may negatively affect fertility. You need enough semen to transport sperm, and fructose is needed as an energy source for sperm. Additionally, acidic semen may damage sperm.

Seminal vesicle stones may also block the ejaculatory duct, leading to fertility issues.

Rare issues with the seminal vesicles may be present at birth that could affect fertility, such as agenesis (missing the organ), underdevelopment, and cysts.

Seminal vesicles and the prostate

Because of the close proximity of the seminal vesicles and the prostate gland, prostate cancer can easily spread to the seminal vesicles. This makes the cancer more difficult to treat. Surgery to remove the seminal vesicles may also be needed to treat prostate cancer.